The Nalunaq Gold Mine contains hanging wall rocks (pictured) which are Paleoproterozoic amphibolite-facies metadolerites. Credit: James St. John
GOLD has been found in geologically unusual circumstances about 250km east of Carnarvon on the margin of the Japan-sized former continent which forms part of the Gascoyne.The gold deposit is found along the margin where two tectonic plates, the Yilgarn Craton and Glenburgh Terrane, collided about two billion years ago.
The Glenburgh Terrane later became trapped between the Yilgarn and Pilbara Cratons, thereby forming a single tectonic plate.
Geological Survey of Western Australia geologist Lisa Roche says the ore is classed as upper amphibolite to granulite facies, which means it has been exposed to a massive seven to 10 kilobars of pressure and temperatures of 500-1000 degrees Celcius.
“Gold deposits in upper amphibolite to granulite facies rocks are quite rare,” she says.
“Known examples commonly attract debate as to whether they actually formed at these high pressures and temperatures or instead were formed early and subsequently metamorphosed or formed late and after peak metamorphism.”
Ms Roche, who has been studying the formation as part of the Geological Survey Masters Program, says the gold had almost certainly been deposited before the tectonic plates met.
She came to this conclusion after nine months of field mapping, visual drill core logging, thin-section petrography and analysis of the microstructure of the gold grains themselves.
“We looked at the internal structure of the gold itself and we found features that suggested it had been through post depositional processes such as deformation, metamorphism or weathering,” she says.
Low silver levels suggest formation processes
Those features included low silver levels of one to three per cent in the gold, whereas gold typically contains five to 20 per cent silver when it first crystallises.
“We could see the gold itself was actually made up of several smaller gold grains, and in between these gold grains there were high purity gold veinlets,” she says.
“They form when silver’s being leached from the gold and removed along the grain boundaries.”
She says this showed the gold had been deformed or metamorphosed.
They also found well-rounded inclusions of pyrrhotite, a sulfide commonly associated with gold mineralising fluids.
“We’ve interpreted this as a peak metamorphic mineral, so that suggested a sulfide phase was present in the host rock before the peak of metamorphism,” she says.
“These observations all have suggested to us that the gold mineralising event occurred before the peak metamorphism.”
As the rocks metamorphosed when the plates collided she says they concluded the gold must be even older.
Note: The above post is reprinted from materials provided by ScienceNetwork WA. The original article was written by Geoff Vivian.
A schematic drawing of template-assisted ligation, shown in this model to give rise to autocatalytic systems. Credit: Maslov and Tkachenko
When life on Earth began nearly 4 billion years ago, long before humans, dinosaurs or even the earliest single-celled forms of life roamed, it may have started as a hiccup rather than a roar: small, simple molecular building blocks known as “monomers” coming together into longer “polymer” chains and falling apart in the warm pools of primordial ooze over and over again.
Then, somewhere along the line, these growing polymer chains developed the ability to make copies of themselves. Competition between these molecules would allow the ones most efficient at making copies of themselves to do so faster or with greater abundance, a trait that would be shared by the copies they made. These rapid replicators would fill the soup faster than the other polymers, allowing the information they encoded to be passed on from one generation to another and, eventually, giving rise to what we think of today as life.
Or so the story goes. But with no fossil record to check from those early days, it’s a narrative that still has some chapters missing. One question in particular remains problematic: what enabled the leap from a primordial soup of individual monomers to self-replicating polymer chains?
A new model published this week in The Journal of Chemical Physics, from AIP Publishing, proposes a potential mechanism by which self-replication could have emerged. It posits that template-assisted ligation, the joining of two polymers by using a third, longer one as a template, could have enabled polymers to become self-replicating.
“We tried to fill this gap in understanding between simple physical systems to something that can behave in a life-like manner and transmit information,” said Alexei Tkachenko, a researcher at Brookhaven National Laboratory. Tkachenko carried out the research alongside Sergei Maslov, a professor at the University of Illinois at Urbana-Champaign with joint appointment at Brookhaven.
Origins of Self-Replication
Self-replication is a complicated process — DNA, the basis for life on earth today, requires a coordinated cohort of enzymes and other molecules in order to duplicate itself. Early self-replicating systems were surely more rudimentary, but their existence in the first place is still somewhat baffling.
Tkachenko and Maslov have proposed a new model that shows how the earliest self-replicating molecules could have worked. Their model switches between “day” phases, where individual polymers float freely, and “night” phases, where they join together to form longer chains via template-assisted ligation. The phases are driven by cyclic changes in environmental conditions, such as temperature, pH, or salinity, which throw the system out of equilibrium and induce the polymers to either come together or drift apart.
According to their model, during the night cycles, multiple short polymers bond to longer polymer strands, which act as templates. These longer template strands hold the shorter polymers in close enough proximity to each other that they can ligate to form a longer strand — a complementary copy of at least part of the template. Over time, the newly synthesized polymers come to dominate, giving rise to an autocatalytic and self-sustaining system of molecules large enough to potentially encode blueprints for life, the model predicts
Polymers can also link together without the aid of a template, but the process is somewhat more random — a chain that forms in one generation will not necessarily be carried over into the next. Template-assisted ligation, on the other hand, is a more faithful means of preserving information, as the polymer chains of one generation are used to build the next. Thus, a model based on template-assisted ligation combines the lengthening of polymer chains with their replication, providing a potential mechanism for heritability.
While some previous studies have argued that a mix of the two is necessary for moving a system from monomers to self-replicating polymers, Maslov and Tkachenko’s model demonstrates that it is physically possible for self-replication to emerge with only template-assisted ligation.
“What we have demonstrated for the first time is that even if all you have is template-assisted ligation, you can still bootstrap the system out of primordial soup,” said Maslov.
The idea of template-assisted ligation driving self-replication was originally proposed in the 1980s, but in a qualitative manner. “Now it’s a real model that you can run through a computer,” said Tkachenko. “It’s a solid piece of science to which you can add other features and study memory effects and inheritance.”
Under Tkachenko and Maslov’s model, the move from monomers to polymers is a very sudden one. It’s also hysteretic — that is, it takes a very certain set of conditions to make the initial leap from monomers to self-replicating polymers, but those stringent requirements are not necessary to maintain a system of self-replicating polymers once one has leapt over the first hurdle.
One limitation of the model that the researchers plan to address in future studies is its assumption that all polymer sequences are equally likely to occur. Transmission of information requires heritable variation in sequence frequencies — certain combinations of bases code for particular proteins, which have different functions. The next step, then, is to consider a scenario in which some sequences become more common than others, allowing the system to transmit meaningful information.
Maslov and Tkachenko’s model fits into the currently favored RNA world hypothesis — the belief that life on earth started with autocatalytic RNA molecules that then lead to the more stable but more complex DNA as a mode of inheritance. But because it is so general, it could be used to test any origins of life hypothesis that relies on the emergence of a simple autocatalytic system.
“The model, by design, is very general,” said Maslov. “We’re not trying to address the question of what this primordial soup of monomers is coming from” or the specific molecules involved. Rather, their model shows a physically plausible path from monomer to self-replicating polymer, inching a step closer to understanding the origins of life.
Background: Waiter, there’s an RNA in my Primordial Soup — Tracing the Origins of Life, from Darwin to Today
Nearly every culture on earth has an origins story, a legend explaining its existence. We humans seem to have a deep need for an explanation of how we ended up here, on this small planet spinning through a vast universe. Scientists, too, have long searched for our origins story, trying to discern how, on a molecular scale, the earth shifted from a mess of inorganic molecules to an ordered system of life. The question is impossible to answer for certain — there’s no fossil record, and no eyewitnesses. But that hasn’t stopped scientists from trying.
Over the past 150 years, our shifting understanding of the origins of life has mirrored the emergence and development of the fields of organic chemistry and molecular biology. That is, increased understanding of the role that nucleotides, proteins and genes play in shaping our living world today has also gradually improved our ability to peer into their mysterious past.
When Charles Darwin published his seminal On the Origin of the Species in 1859, he said little about the emergence of life itself, possibly because, at the time, there was no way to test such ideas. His only real remarks on the subject come from a later letter to a friend, in which he suggested a that life emerged out of a “warm little pond” with a rich chemical broth of ions. Nevertheless, Darwin’s influence was far-reaching, and his offhand remark formed the basis of many origins of life scenarios in the following years.
In the early 20th century, the idea was popularized and expanded upon by a Russian biochemist named Alexander Oparin. He proposed that the atmosphere on the early earth was reducing, meaning it had an excess of negative charge. This charge imbalance could catalyze existing a prebiotic soup of organic molecules into the earliest forms of life.
Oparin’s writing eventually inspired Harold Urey, who began to champion Oparin’s proposal. Urey then caught the attention of Stanley Miller, who decided to formally test the idea. Miller took a mixture of what he believed the early earth’s oceans may have contained — a reducing mixture of methane, ammonia, hydrogen, and water — and activated it with an electric spark. The jolt of electricity, acting like a strike of lightening, transformed nearly half of the carbon in the methane into organic compounds. One of the compounds he produced was glycine, the simplest amino acid.
The groundbreaking Miller-Urey experiment showed that inorganic matter could give rise to organic structures. And while the idea of a reducing atmosphere gradually fell out of favor, replaced by an environment rich in carbon dioxide, Oparin’s basic framework of a primordial soup rich with organic molecules stuck around.
The identification of DNA as the hereditary material common to all life, and the discovery that DNA coded for RNA, which coded for proteins, provided fresh insight into the molecular basis for life. But it also forced origins of life researchers to answer a challenging question: how could this complicated molecular machinery have started? DNA is a complex molecule, requiring a coordinated team of enzymes and proteins to replicate itself. Its spontaneous emergence seemed improbable.
In the 1960s, three scientists — Leslie Orgel, Francis Crick and Carl Woese — independently suggested that RNA might be the missing link. Because RNA can self-replicate, it could have acted as both the genetic material and the catalyst for early life on earth. DNA, more stable but more complex, would have emerged later.
Today, it is widely believed (though by no means universally accepted) that at some point in history, an RNA-based world dominated the earth. But how it got there — and whether there was a simpler system before it — is still up for debate. Many argue that RNA is too complicated to have been the first self-replicating system on earth, and that something simpler preceded it.
Graham Cairns-Smith, for instance, has argued since the 1960s that the earliest gene-like structures were not based on nucleic acids, but on imperfect crystals that emerged from clay. The defects in the crystals, he believed, stored information that could be replicated and passed from one crystal to another. His idea, while intriguing, is not widely accepted today.
Others, taken more seriously, suspect that RNA may have emerged in concert with peptides — an RNA-peptide world, in which the two worked together to build up complexity. Biochemical studies are also providing insight into simpler nucleic acid analogs that could have preceded the familiar bases that make up RNA today. It’s also possible that the earliest self-replicating systems on earth have left no trace of themselves in our current biochemical systems. We may never know, and yet, the challenge of the search seems to be part of its appeal.
Recent research by Tkachenko and Maslov, published July 28, 2015 in The Journal of Chemical Physics, suggests that self-replicating molecules such as RNA may have arisen through a process called template-assisted ligation. That is, under certain environmental conditions, small polymers could be driven to bond to longer complementary polymer template strands, holding the short strands in close enough proximity to each other that they could fuse into longer strands. Through cyclic changes in environmental conditions that induce complementary strands to come together and then fall apart repeatedly, a self-sustaining collection of hybridized, self-replicating polymers able to encode the blueprints for life could emerge.
Reference:
Alexei Tkachenko and Sergei Maslov. Spontaneous emergence of autocatalytic information-coding polymers. The Journal of Chemical Physics, 2015 DOI: 10.1063/1.4922545
Magnetic field strength in the South Atlantic Anomaly is shown. Credit: Graphic by Michael Osadciw/University of Rochester.
A team of researchers has for the first time recovered a magnetic field record from ancient minerals for Iron Age southern Africa (between 1000 and 1500 AD). The data, combined with the current weakening of Earth’s magnetic field, suggest that the region of Earth’s core beneath southern Africa may play a special role in reversals of the planet’s magnetic poles.
The team was led by geophysicist John Tarduno from the University of Rochester and included researchers from Witwatersrand University and Kwa-Zulu Natal University of South Africa.
Reversals of the North and South Poles have occurred irregularly throughout history, with the last one taking place about 800,000 years ago. Once a reversal starts, it can take as long as 15,000 years to complete. The new data suggests the core region beneath southern Africa may be the birthplace of some of the more recent and future pole reversals.
“It has long been thought reversals start at random locations, but our study suggests this may not be the case,” said Tarduno, a leading expert on Earth’s magnetic field.
The results have been published in the latest issue of the journal Nature Communications.
Tarduno collected the data for his study from five sites along South Africa’s borders with Zimbabwe and Botswana, near the Limpopo River. That part of Africa belongs to a region called the South Atlantic Anomaly–extending west beyond South America–that today has an unusually weak magnetic field strength.
Earth’s dipole magnetic field strength has decreased 16 percent since 1840–with most of the decay related to the weakening field in the South Atlantic Anomaly–leading to much speculation that the planet is in the early stages of a field reversal. As Tarduno points out, it is only speculation because weakening magnetic fields can recover without leading to a reversal of the poles.
Tarduno and his fellow-researchers believe they found the reason for the unusually low magnetic field strength in that region of the Southern Hemisphere.
“The top of the core beneath this region is overlain by unusually hot and dense mantle rock,” said Tarduno.
That hot and dense mantle rock lies 3000 km below the surface, has steep sides, and is about 6000 km across, which is roughly the distance from New York to Paris.
Together with Eric Blackman, an astrophysicist at the University of Rochester, and Michael Watkeys, a geologist at the University of KwaZulu-Natal in South Africa, Tarduno hypothesizes that the region–which is referred to as a Large Low Shear Velocity Province (LLSVP)–affects the direction of the churning liquid iron that generates Earth’s magnetic field. Tarduno says it’s the shift in the flow of liquid iron that causes irregularities in the magnetic field, ultimately resulting in a loss of magnetic intensity, giving the region its characteristically low magnetic field strength.
Until now, researchers have relied solely on estimates from models derived from data collected at other global sites for an Iron Age record of the magnetic field of southern Africa. Tarduno and his team wanted hard data on both the intensity and direction of the magnetic field, which are recorded and stored in minerals, such as magnetite, at the time they were formed.
The researchers were able to get their data thanks to a knowledge of ancient African practices–in this case, the ritualistic cleansing of villages in agricultural communities. Archeologist Thomas Huffman of Witwatersrand University, a member of the research team and a leading authority on Iron Age southern Africa, explains that villages were cleansed by burning down huts and grain bins. The burning clay floors reached a temperature in excess of 1000 ?C, hot enough to erase the magnetic information stored in the magnetite and create a new record of the magnetic field strength and direction at the time of the burning.
Tarduno and his team found a sharp 30 percent drop in magnetic field intensity from 1225 to 1550 AD. Given that the field intensity in the region is also declining today–though less rapidly, as measured by satellites–the research team believes that the process causing the weakening field may be a recurring feature of the magnetic field.
“Because rock in the deep mantle moves less than a centimeter a year, we know the LLSVP is ancient, meaning it may be a longstanding site for the loss of magnetic field strength,” said Tarduno. “And it is also possible that the region may actually be a trigger for magnetic pole reversals, which might happen if the weak field region becomes very large.”
Earth’s dipole magnetic field strength has decreased 16 percent since 1840, leading to much speculation that the planet is in the early stages of a field reversal. Most of the global decay of intensity is related to the weakening field of the Southern Hemisphere that includes Southern Africa.
Tarduno points out that the new data cannot be used to predict with confidence that the present-day magnetic field is entering a reversal. However, it does suggest that the present-day pattern may be the latest manifestation of a repeating feature that occasionally leads to a global field reversal.
Reference:
John A. Tarduno, Michael K. Watkeys, Thomas N. Huffman, Rory D. Cottrell, Eric G. Blackman, Anna Wendt, Cecilia A. Scribner, Courtney L. Wagner. Antiquity of the South Atlantic Anomaly and evidence for top-down control on the geodynamo. Nature Communications, 2015; 6: 7865 DOI: 10.1038/ncomms8865
Scientists followed the journey of water through the Tarim Basin from the rivers at the edge of the valley to the desert aquifers under the basin. They found that as water moved through irrigated fields, the water gathered dissolved carbon and moved it deep underground. Credit: Yan Li
The world’s deserts may be storing some of the climate-changing carbon dioxide emitted by human activities, a new study suggests. Massive aquifers underneath deserts could hold more carbon than all the plants on land, according to the new research.
Humans add carbon dioxide to the atmosphere through fossil fuel combustion and deforestation. About 40 percent of this carbon stays in the atmosphere and roughly 30 percent enters the ocean, according to the University Corporation for Atmospheric Research. Scientists thought the remaining carbon was taken up by plants on land, but measurements show plants don’t absorb all of the leftover carbon. Scientists have been searching for a place on land where the additional carbon is being stored—the so-called “missing carbon sink.”
The new study suggests some of this carbon may be disappearing underneath the world’s deserts – a process exacerbated by irrigation. Scientists examining the flow of water through a Chinese desert found that carbon from the atmosphere is being absorbed by crops, released into the soil and transported underground in groundwater—a process that picked up when farming entered the region 2,000 years ago.
Underground aquifers store the dissolved carbon deep below the desert where it can’t escape back to the atmosphere, according to the new study.
The new study estimates that because of agriculture roughly 14 times more carbon than previously thought could be entering these underground desert aquifers every year. These underground pools that taken together cover an area the size of North America may account for at least a portion of the “missing carbon sink” for which scientists have been searching.
“The carbon is stored in these geological structures covered by thick layers of sand, and it may never return to the atmosphere,” said Yan Li, a desert biogeochemist with the Chinese Academy of Sciences in Urumqi, Xinjiang, and lead author of the study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union. “It is basically a one-way trip.”
Knowing the locations of carbon sinks could improve models used to predict future climate change and enhance calculations of the Earth’s carbon budget, or the amount of fossil fuels humans can burn without causing major changes in the Earth’s temperature, according to the study’s authors.
Although there are most likely many missing carbon sinks around the world, desert aquifers could be important ones, said Michael Allen, a soil ecologist from the Center for Conservation Biology at the University of California-Riverside who was not an author on the new study.
If farmers and water managers understand the role heavily-irrigated inland deserts play in storing the world’s carbon, they may be able to alter how much carbon enters these underground reserves, he said.
“This means [managers] can take practical steps that could play a role in addressing carbon budgets,” said Allen.
Examining desert water
To find out where deserts tucked away the extra carbon, Li and his colleagues analyzed water samples from the Tarim Basin, a Venezuela-sized valley in China’s Xinjiang region. Water draining from rivers in the surrounding mountains support farms that edge the desert in the center of the basin.
The researchers measured the amount of carbon in each water sample and calculated the age of the carbon to figure out how long the water had been in the ground.
The study shows the amount of carbon dioxide dissolved in the water doubles as it filters through irrigated fields. The scientists suggest carbon dioxide in the air is taken up by the desert crops. Some of this carbon is released into the soil through the plant’s roots. At the same time, microbes also add carbon dioxide to the soil when they break down sugars in the dirt. In a dry desert, this gas would work its way out of the soil into the air. But on arid farms, the carbon dioxide emitted by the roots and microbes is picked up by irrigation water, according to the new study.
In these dry regions, where water is scarce, farmers over-irrigate their land to protect their crops from salts that are left behind when water used for farming evaporates. Over-irrigating washes these salts, along with carbon dioxide that is dissolved in the water, deeper into the earth, according to the new study.
Although this process of carbon burial occurs naturally, the scientists estimate that the amount of carbon disappearing under the Tarim Desert each year is almost 12 times higher because of agriculture. They found that the amount of carbon entering the desert aquifer in the Tarim Desert jumped around the time the Silk Road, which opened the region to farming, begin to flourish.
After the carbon-rich water flows down into the aquifer near the farms and rivers, it moves sideways toward the middle of the desert, a process that takes roughly 10,000 years.
Any carbon dissolved in the water stays underground as it makes its way through the aquifer to the center of the desert, where it remains for thousands of years, according to the new study.
Estimating carbon storage
Based on the various rates that carbon entered the desert throughout history, the study’s authors estimate 20 billion metric tons (22 billion U.S. tons) of carbon is stored underneath the Tarim Basin desert, dissolved in an aquifer that contains roughly 10 times the amount of water held in the North American Great Lakes.
The study’s authors approximate the world’s desert aquifers contain roughly 1 trillion metric tons (1 trillion U.S. tons) of carbon—about a quarter more than the amount stored in living plants on land.
Li said more information about water movement patterns and carbon measurements from other desert basins are needed to improve the estimate of carbon stored underneath deserts around the globe.
Allen said the new study is “an early foray” into this research area. “It is as much a call for further research as a definitive final answer,” he said.
Reference:
Yan Li, Yu-Gang Wang, R. A. Houghton, Li-Song Tang. Hidden carbon sink beneath desert. DOI: 10.1002/2015GL064222
This is a time series of the Blackwater River valley. Top: Intact marsh surveyed from AD 1902 to AD 1904 and presented in a 7.5″ USGS topographic map from AD 1905; dark blue hatching around the Blackwater valley is tidal marsh; light blue pattern is freshwater swamp. Middle: Initiation of major ponding seen in an aerial photograph from AD 1938. Bottom: Coalesced ponds forming the informal ‘Lake Blackwater’ in satellite imagery from AD 2007. Credit: GSA Today, DeJong et al., and credits within the caption.
In a new article for GSA Today, authors Benjamin DeJong and colleagues write that sea-level rise (3.4 mm/yr) is faster in the Chesapeake Bay region than any other location on the Atlantic coast of North America, and twice the global average (1.7 mm/yr). They have found that dated interglacial deposits suggest that relative sea levels in the Chesapeake Bay region deviate from global trends over a range of timescales.
According to DeJong and colleagues, “Glacio-isostatic adjustment of the land surface from loading and unloading of continental ice is likely responsible for these deviations, but our understanding of the scale and timeframe over which isostatic response operates in this region remains incomplete because dated sea-level proxies are mostly limited to the Holocene and to deposits 80 ka or older.”
To better understand glacio-isostatic control over past and present relative sea level, DeJong and colleagues applied a suite of dating methods to the stratigraphy of the Blackwater National Wildlife Refuge, one of the most rapidly subsiding and lowest-elevation surfaces bordering Chesapeake Bay. Their data indicate that the region was submerged at least for portions of marine isotope stage (MIS) 3 (about 30 to 60 thousand years ago), although, they note, multiple proxies suggest that global sea level was 40 to 80 meters lower than today.
Today, MIS 3 deposits are above sea level because they were raised by the Last Glacial Maximum forebulge, but decay of that same forebulge is causing ongoing subsidence. “These results,” they write, “suggest that glacio-isostasy controlled relative sea level in the mid-Atlantic region for tens of thousands of years following retreat of the Laurentide Ice Sheet and continues to influence relative sea level in the region.”
The study finds that isostatically driven subsidence of the Chesapeake Bay region will continue for millennia, exacerbating the effects of global sea-level rise and impacting the region’s large population centers and valuable coastal natural resources.
The Tyrannosaurus rex and its fellow theropod dinosaurs that rampage across the screen in movies like Jurassic World were successful predators partly due to a unique, deeply serrated tooth structure that allowed them to easily tear through the flesh and bone of other dinosaurs, says new research from the University of Toronto Mississauga (UTM).
The research, published in the journal Scientific Reports, was conducted by Kirstin Brink, a post-doctoral researcher in the Department of Biology at UTM; Professor Robert Reisz of the Department of Biology and the UTM vice-principal of graduate studies; and colleagues at the Royal Ontario Museum (ROM) and the National Synchrotron Radiation Research Center in Taiwan.
Brink and her colleagues determined that this deeply serrated—or sawlike—tooth structure is uniquely common to carnivorous theropods such as T. rex and Allosaurus, and even one of the first theropods, Coelophysis. Other extinct animals had teeth that were superficially similar, but it was the special arrangement of tissues inside the tooth that strengthened and improved the function of the teeth. The deep serrations made them much more efficient at chomping on bones and ripping flesh of larger animals and reptiles, and allowed them to prosper for about 165 million years as fearsome, top predators.
The only reptile living today that has the same superficial tooth structure is the Komodo dragon, native to Indonesia. It, too, preys on larger animals.
A detail of a thin section through the tooth of a large theropod, Gorgosaurus, from Alberta. Credit: Danielle Default
“What is so fascinating to me is that all animal teeth are made from the same building blocks, but the way the blocks fit together to form the structure of the tooth greatly affects how that animal processes food,” Brink said. “The hidden complexity of the tooth structure in theropods suggests that they were more efficient at handling prey than previously thought, likely contributing to their success.”
She and her colleagues also found that the unique arrangement of tooth tissues did not develop in response to these carnivores chewing hard materials. They determined this by examining samples of dinosaur teeth that had not yet broken through the gums, as well as samples from mature dinosaur teeth. Unlike humans, reptiles grow new teeth throughout their lifetimes.
“What is startling and amazing about this work is that Kirstin was able to take teeth with these steak knife-like serrations and find a way to make cuts to obtain sections along the cutting edge of these teeth,” said Reisz. “If you don’t cut them right, you don’t get the information.
“This brought about a developmental explanation for the tooth formation; the serrations are even more spectacular and permanent.”
Brink and colleagues used a scanning electron microscope – a very powerful microscope—and a synchrotron – a microscope that allows the user to understand a substance’s chemical composition—to do a thorough examination and analysis of tooth slices from eight carnivorous theropods, including T. rex, Allosaurus, Coelophysis and Gorgosaurus. The samples came from various museums, including the ROM, the Canadian Museum of Nature in Ottawa, and the Royal Tyrrell Museum in Alberta.
Reisz noted that his research lab has focused on teeth in the context of their workings within the jaw, making possible a broader understanding of the value of this discovery.
This map shows the Younger Dryas Boundary locations that provided data for the analysis. Credit: UCSB
At the end of the Pleistocene period, approximately 12,800 years ago — give or take a few centuries — a cosmic impact triggered an abrupt cooling episode that earth scientists refer to as the Younger Dryas.
New research by UC Santa Barbara geologist James Kennett and an international group of investigators has narrowed the date to a 100-year range, sometime between 12,835 and 12,735 years ago. The team’s findings appear today in the Proceedings of the National Academy of Sciences.
The researchers used Bayesian statistical analyses of 354 dates taken from 30 sites on more than four continents. By using Bayesian analysis, the researchers were able to calculate more robust age models through multiple, progressive statistical iterations that consider all related age data.
“This range overlaps with that of a platinum peak recorded in the Greenland ice sheet and of the onset of the Younger Dryas climate episode in six independent key records,” explained Kennett, professor emeritus in UCSB’s Department of Earth Science. “This suggests a causal connection between the impact event and the Younger Dryas cooling.”
In a previous paper, Kennett and colleagues conclusively identified a thin layer called the Younger Dryas Boundary (YDB) that contains a rich assemblage of high-temperature spherules, melt-glass and nanodiamonds, the production of which can be explained only by cosmic impact. However, in order for the major impact theory to be possible, the YDB layer would have to be the same age globally, which is what this latest paper reports.
“We tested this to determine if the dates for the layer in all of these sites are in the same window and statistically whether they come from the same event,” Kennett said. “Our analysis shows with 95 percent probability that the dates are consistent with a single cosmic impact event.”
All together, the locations cover a huge range of distribution, reaching from northern Syria to California and from Venezuela to Canada. Two California sites are on the Channel Islands off Santa Barbara.
However, Kennett and his team didn’t rely solely on their own data, which mostly used radiocarbon dating to determine date ranges for each site. They also examined six instances of independently derived age data that used other dating methods, in most cases counting annual layers in ice and lake sediments.
Two core studies taken from the Greenland ice sheet revealed an anomalous platinum layer, a marker for the YDB. A study of tree rings in Germany also showed evidence of the YDB, as did freshwater and marine varves, the annual laminations that occur in bodies of water. Even stalagmites in China displayed signs of abrupt climate change around the time of the Younger Dryas cooling event.
“The important takeaway is that these proxy records suggest a causal connection between the YDB cosmic impact event and the Younger Dryas cooling event,” Kennett said. “In other words, the impact event triggered this abrupt cooling.
“The chronology is very important because there’s been a long history of trying to figure out what caused this anomalous and enigmatic cooling,” he added. “We suggest that this paper goes a long way to answering that question and hope that this study will inspire others to use Bayesian statistical analysis in similar kinds of studies because it’s such a powerful tool.”
Reference:
James P. Kennett, Douglas J. Kennett, Brendan J. Culleton, J. Emili Aura Tortosa, James L. Bischoff, Ted E. Bunch, I. Randolph Daniel Jr., Jon M. Erlandson, David Ferraro, Richard B. Firestone, Albert C. Goodyear, Isabel Israde-Alcántara, John R. Johnson, Jesús F. Jordá Pardo, David R. Kimbel, Malcolm A. LeCompte, Neal H. Lopinot, William C. Mahaney, Andrew M. T. Moore, Christopher R. Moore, Jack H. Ray, Thomas W. Stafford Jr., Kenneth Barnett Tankersley, James H. Wittke, Wendy S. Wolbach, and Allen West. Bayesian chronological analyses consistent with synchronous age of 12,835–12,735 Cal B.P. for Younger Dryas boundary on four continents. PNAS, July 2015 DOI: 10.1073/pnas.1507146112
Note: The above post is reprinted from materials provided by University of California – Santa Barbara. The original item was written by Julie Cohen.
This artist’s concept compares Earth (left) to the new planet, called Kepler-452b, which is about 60 percent larger in diameter. Credit: NASA/JPL-Caltech/T. Pyle
NASA’s Kepler mission has confirmed the first near-Earth-size planet in the “habitable zone” around a sun-like star. This discovery and the introduction of 11 other new small habitable zone candidate planets mark another milestone in the journey to finding another “Earth.”
The newly discovered Kepler-452b is the smallest planet to date discovered orbiting in the habitable zone — the area around a star where liquid water could pool on the surface of an orbiting planet — of a G2-type star, like our sun. The confirmation of Kepler-452b brings the total number of confirmed planets to 1,030.
“On the 20th anniversary year of the discovery that proved other suns host planets, the Kepler exoplanet explorer has discovered a planet and star which most closely resemble the Earth and our Sun,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate at the agency’s headquarters in Washington. “This exciting result brings us one step closer to finding an Earth 2.0.”
Kepler-452b is 60 percent larger in diameter than Earth and is considered a super-Earth-size planet. While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.
While Kepler-452b is larger than Earth, its 385-day orbit is only 5 percent longer. The planet is 5 percent farther from its parent star Kepler-452 than Earth is from the Sun. Kepler-452 is 6 billion years old, 1.5 billion years older than our sun, has the same temperature, and is 20 percent brighter and has a diameter 10 percent larger.
“We can think of Kepler-452b as an older, bigger cousin to Earth, providing an opportunity to understand and reflect upon Earth’s evolving environment,” said Jon Jenkins, Kepler data analysis lead at NASA’s Ames Research Center in Moffett Field, California, who led the team that discovered Kepler-452b. “It’s awe-inspiring to consider that this planet has spent 6 billion years in the habitable zone of its star; longer than Earth. That’s substantial opportunity for life to arise, should all the necessary ingredients and conditions for life exist on this planet.”
To help confirm the finding and better determine the properties of the Kepler-452 system, the team conducted ground-based observations at the University of Texas at Austin’s McDonald Observatory, the Fred Lawrence Whipple Observatory on Mt. Hopkins, Arizona, and the W. M. Keck Observatory atop Mauna Kea in Hawaii. These measurements were key for the researchers to confirm the planetary nature of Kepler-452b, to refine the size and brightness of its host star and to better pin down the size of the planet and its orbit.
The Kepler-452 system is located 1,400 light-years away in the constellation Cygnus. The research paper reporting this finding has been accepted for publication in The Astronomical Journal.
In addition to confirming Kepler-452b, the Kepler team has increased the number of new exoplanet candidates by 521 from their analysis of observations conducted from May 2009 to May 2013, raising the number of planet candidates detected by the Kepler mission to 4,696. Candidates require follow-up observations and analysis to verify they are actual planets.
Twelve of the new planet candidates have diameters between one to two times that of Earth, and orbit in their star’s habitable zone. Of these, nine orbit stars that are similar to our sun in size and temperature.
“We’ve been able to fully automate our process of identifying planet candidates, which means we can finally assess every transit signal in the entire Kepler dataset quickly and uniformly,” said Jeff Coughlin, Kepler scientist at the SETI Institute in Mountain View, California, who led the analysis of a new candidate catalog. “This gives astronomers a statistically sound population of planet candidates to accurately determine the number of small, possibly rocky planets like Earth in our Milky Way galaxy.”
These findings, presented in the seventh Kepler Candidate Catalog, will be submitted for publication in the Astrophysical Journal.
Scientists now are producing the last catalog based on the original Kepler mission’s four-year data set. The final analysis will be conducted using sophisticated software that is increasingly sensitive to the tiny telltale signatures of Earth-size planets.
Note: The above post is reprinted from materials provided by NASA.
The location of the volcanic islands Tristan da Cunha and Gough in the South Atlantic. Image Reproduced from the GEBCO world map 2014
Located in the South Atlantic, thousands of kilometers away from the nearest populated country, Tristan da Cunha is one of the remotest inhabited islands on earth. Together with the uninhabited neighboring island of Gough about 400 kilometers away, it is part of the British Overseas Territories. Both islands are active volcanoes, derived from the same volcanic hotspot. A team of marine scientists and volcanologists from the GEOMAR Helmholtz Centre for Ocean Research Kiel, from the University of Kiel and the University of London discovered that about 70 million years ago, the composition of the material from the Tristan-Gough hotspot deposited on the seafloor changed. In the international scientific journal Nature Communications, the team provides an explanation for this compositional change that could help explain similar findings in other hotspots worldwide.
Volcanic hotspots can be found in all oceans. “Pipe-like structures, so-called ‘Mantle Plumes’, transport hot material from the earth’s interior to the base of the earth’s lithospheric plates. As the mantle material rises beneath the plate, pressure release melting takes places and these melts rise to the surface forming volcanoes on the seafloor,” explains Professor Kaj Hoernle from GEOMAR, lead author of the current study. As the earth’s plates move over the hotspots, the volcanoes are moved away from their sources but new volcanoes form above the hotspots. “As a result long chains of extinct volcanoes extend from the active volcano located above the hotspot for over thousands of kilometers in the direction of plate motion,” adds the volcanologist.
Unlike most other hotspots, scientists can trace the history of the Tristan-Gough hotspot back to its initiation. Huge outpourings of flood basalts in Etendeka and Brazil at the initiation of the hotspot 132 million years ago most likely contributed to the breaking apart of the Gondwana supercontinent into new continents including Africa and South America. The rifting apart of Africa and South America has led to the formation of the South Atlantic Ocean basin. As the Atlantic widened, two underwater mountain ranges (the Walvis Ridge and Guyot Province on the African Plate and the Rio Grande Rise on the South American Plate) formed above the hotspot. The active volcanic islands of Tristan da Cuhna and Gough lie at the end of the track on the African Plate.
Several expeditions, including two with the German research vessel SONNE (I) led by Kiel researchers, recovered samples from these submarine mountains. Geochemical analyzes show that the oldest parts of the Walvis Ridge, as well as the intial volcanic outpourings on the continents, have compositions similar to the presently active Gough volcano. The northwestern part of the Walvis Ridge and Guyot Province younger than 70 million years, however, is divided into two geographically distinct geochemical domains: “The southern part also shows the geochemically enriched Gough signature, while the northern part is geochemically less enriched, similar to the present Tristan da Cunha Volcano,” says co-author Joana Rohde.
A very likely explanation is hidden more than 2,500 kilometers deep in the Earth’s lower mantle. At the base of the lower mantle beneath southern Africa, seismic surveys have shown a huge lens of material, which has different physical properties than the surrounding mantle material. This lens is called a “Large Low Shear Velocity Province” (LLSVP). The Tristan-Gough hotspot is located above the margin of this LLSVP. “In its early stages, the plume only appears to have sucked in material from the LLSVP,” explains Professor Hoernle, “but over the course of time the LLSVP material at the NW side of the margin was exhausted and material from outside the LLSVP was drawn into the base of the plume.” Since then, the plume has contained two types of compositionally distinct mantle, leading to the formation of parallel but compositionally distinct plume subtracks. “At some point in the future, the plume might be completely cut off from the LLSVP lens, again erupting only one type of composition, but now Tristan rather than Gough type of material.” says the volcanologist.
This model is also applicable to other hotspot tracks such as Hawaii. There, too, is evidence that parallel chains of volcanoes emit geochemically distinct material with one or the other composition dominating at different times in the history of the hotspot. A second LLSVP exists beneath the Pacific. “Thanks to the investigations at the Tristan-Gough-Hotspot, we now understand better the mysterious processes taking place in the interior of our planet,” says Professor Hoernle.
Reference:
Kaj Hoernle, Joana Rohde, Folkmar Hauff, Dieter Garbe-Schönberg, Stephan Homrighausen, Reinhard Werner, Jason P. Morgan. How and when plume zonation appeared during the 132 Myr evolution of the Tristan Hotspot. Nature Communications, 2015; 6: 7799 DOI: 10.1038/ncomms8799 Note: The above post is reprinted from materials provided by Helmholtz Centre for Ocean Research Kiel (GEOMAR).
Some of the fossils in this study are exceptionally well-preserved, such as the specimen shown here. With micro-CT scanning, the skeleton can be reconstructed in 3D, revealing complete skeletons, fully articulated skulls and fragments. Credit: Kevin de Queiroz
Tiny Anolis lizards preserved since the Miocene in amber are giving scientists a true appreciation of the meaning of community stability. Dating back some 15 to 20 million years, close comparison of these exquisitely preserved lizard fossils with their descendants alive today in the Caribbean has revealed, remarkably, little about them has changed.
“Not only do we see the community structure of these lizards has remained stable for 20 million years, it’s also difficult to tell some of these fossil lizards apart from those alive today,” says Kevin de Queiroz, a herpetologist at the Smithsonian’s National Museum of Natural History and co-author of a study which appeared today in the Proceedings of the National Academy of Sciences.
After first appearing on each of the four Greater Antillean Islands some 50 million years ago, Anolis lizards spread out on each island to occupy various niches in island trees. Some ended up living high-up in the canopy area, others low down on the trunk near the ground; others established themselves in the mid-trunk area while others adapted and thrived on the twigs. Each new species developed its own distinct body type, called an ecomorph, shaped by the specific tree niche where it lived.
Until recently, scientists had only indirect estimates based on amounts and patterns of molecular (DNA sequence) divergence as to just how long this community structure of tree-living lizards, each specialized to a different niche and living together, had existed in the Antilles. Now, amber fossils reveal it has been an incredibly long time: some 20 million years or greater. Four modern ecomorph body types (trunk-crown, trunk-ground, trunk and twig) are represented in the amber fossils.
“For other types of organisms, like mammals, 20 million years would be quite an extraordinary period for a species to last,” de Queiroz points out. “The community could persist longer than the species, with different species filling the various roles in the same ecological community over time.”
Niche shifts or changes of Anolis lizards occurred independently from island to island, producing ecomorphs on different islands that closely resemble one another. For example, lizards from the trunk-crown area of the tree are normally large- or medium-sized and green, and they resemble one another from island to island. Looks can be misleading, however. Although lizards of the same ecomorph from different islands may look alike, they are more closely related to lizards from their home islands, which may look much more different.
The long-term stability of these lizard communities doesn’t mean their environment has also been stable, de Queiroz adds. “What makes this discovery more remarkable is that these lizard communities have remained stable despite substantial environmental change that has occurred in the Antilles since the Miocene.”
Reference:
“Amber fossils demonstrate deep-time stability of Caribbean lizard communities.” PNAS 2015 ; published ahead of print July 27, 2015, DOI: 10.1073/pnas.1506516112
Earlier finds from Tautavel Credit: AFP Photo/Raymond Roig
A 16-year-old French volunteer archaeologist has found an adult tooth dating back around 560,000 years in southwestern France, in what researchers hailed as a “major discovery” Tuesday.
“A large adult tooth—we can’t say if it was from a male or female—was found during excavations of soil we know to be between 550,000 and 580,000 years old, because we used different dating methods,” paleoanthropologist Amelie Viallet told AFP.
“This is a major discovery because we have very few human fossils from this period in Europe,” she said.
The tooth was found in the Arago cave near the village of Tautavel, one of the world’s most important prehistoric sites which has been excavated for about 50 years.
It is also the site of the discovery of over 140 fossils belonging to Tautavel Man, an early hominid that lived an estimated 450,000 years ago.
Volunteer Camille, 16, was working with another young archaeologist when she found the tooth last Thursday.
They were among the hundreds of young trainee archaeologists who come to work in the cave every year to study human ancestors during the lower Paleolithic era, when they first began to use tools.
The owner of the tooth—a very worn lower incisor—lived during a cold, dry and windy period and according to archaeological finds in the cave, hunted horses, reindeer, bison and rhinoceros.
For a long time the Heidelberg jaw—including the chin and full set of lower teeth—discovered in Germany in 1907 dating to around 600,000 years ago, was the oldest fossil of human ancestors in western Europe.
However some archaeological sites offered up evidence of stone tools dating back much earlier.
This has left many questions and stirred debate about the life and presence of human ancestors in Europe before modern humans rose out of Africa and went on to conquer the planet.
In 2013 the discovery of a fossil tooth in southeastern Spain that dated to about 1.4 million years ago shook up the timeline of the colonisation of Europe by modern humans.
A piece of the puzzle
Dr Matthew Skinner, a palaeoanthropologist from the University of Kent in Britain said that while the find was important as there are few human fossils from this period, “a single tooth, I wouldn’t say is a major discovery, unfortunately.”
“If there’s something about its shape or its size that would suggest that it is different from the other fossils we have from that time period and perhaps belongs to a different species , then that would be of course very interesting.”
He said the most obvious species to which the tooth would belong would be Homo heidelbergensis—owner of the German jaw—about whom little is known.
“These are certainly different from modern humans, they existed before Neanderthals. They had quite large brains and fairly complex behaviour but weren’t modern in the way that we are.
“They were quite robust, very stocky individuals, they had really massive skulls.”
However he said most fossils available came from above the neck, making it difficult to understand the species.
“What we need is for them to find a skeleton …We have lots of skulls of heidelbergensis but what we don’t have are arms and legs and ribs and pelvis… not much, there’s a few pieces, but it’s really not very much.”
Tony Chevalier, another paleoanthropologist from Tautavel, said the tooth would also shine a light on the current debate over Homo Heidelbergensis—owner of the German jaw and ancestor of Neanderthals.
“Was Homo Heidelbergensis simply European or also African? It is a very important debate,” said Chevalier.
While modern Homo sapiens is now the last man standing, in the past our ancestors shared the earth with several early human species at the same time.
A plethora of archaeological finds in past decades continues to change the size and shape of humans’ family tree and the connections between the different branches.
Note: The above post is reprinted from materials provided by AFP.
Notable locations and climbing routes on the southeast face of El Capitan. The names of each climbing route are listed at the top of the route. General locations are shaded orange. The Nose travels along the curving arête separating the sunlit and shaded parts of the cliff. The North America Wall is the concave section of wall to the right of the Nose, marked by mafic dikes in the shape of North America. The exposure visible in this image is the area of Figure 6. Location names and route paths taken from Putnam and Sloan (2014). The scale bar is an approximate horizontal scale; absolute scale varies because the image is a flattened representation of a three-dimensional surface. The view angle is to the north. Photograph courtesy of www. xRez. com. Credit: Photograph courtesy of www. xRez. com, published in Geosphere.
Granitic rocks make up much of Earth’s continental crust and many of the planet’s most iconic landscapes. However, granite’s formation is poorly understood because it happens tens of kilometers below the surface. In this unique study, authors Roger Putnam and colleagues combine decimeter-scale field mapping, rock climbing, and new dating and geochemical analyses to evaluate the timing and intrusive dynamics of the granitic rocks that make up El Capitan in Yosemite National Park, California, USA.
The comparatively accessible southeast face of El Capitan provides a clean, ~1-km-tall exposure of the interior of a granitic system. Putnam and colleagues found this vertical landscape to be a perfect place to test hypotheses regarding the formation of granitic rocks. In their paper published in Geosphere on 1 July 2015, the authors use climbing route designations as landmarks in describing the geology, along with both official and unofficial (e.g., North America; The Alcove) local place names.
They write that many models of granite formation rely on processes such as crystal/liquid segregation that should present a signature visible in the vertical dimension of a granitic system. They found that El Capitan is made up of seven different granitic units that episodically intruded over about three million years. Their chemical and textural analyses of samples collected along vertical transects of the two dominant rocks there, the El Capitan and Taft Granites, reveal no systematic patterns in rock composition. In fact, they conclude, “These data reveal [3 million years of] assembly of the plutonic system and show no evidence for gravity-driven separation of crystals and liquid over the 1 km vertical extent of the cliff,” which, they write, is “hard to reconcile with models of granite formation that envision magma chambers as large, mostly liquid, fractionating bodies.”
Reference:
Plutonism in three dimensions: Field and geochemical relations on the southeast face of El Capitan, Yosemite National Park, California
Roger Putnam et al., University of North Carolina, Chapel Hill, North Carolina, USA. Published online on 1 July 2015; DOI: 10.1130/GES01133.1.
Graduate student Elena Steponaitis takes notes while collecting stalagmite and drip water samples in Lehman Caves, Nevada. Credit: Christine Y. Chen
All around the deserts of Utah, Nevada, southern Oregon, and eastern California, ancient shorelines line the hillsides above dry valley floors, like bathtub rings—remnants of the lakes once found throughout the region. Even as the ice sheets retreated at the end of the last ice age, 12,000 years ago, the region remained much wetter than it is today. The earliest settlers of the region are likely to have encountered a verdant landscape of springs and wetlands.
So just when and why did today’s desert West dry out?
Researchers from MIT and elsewhere have now determined that the western U.S.—a region including Nevada, Utah, Oregon, and parts of California—was a rather damp setting until approximately 8,200 years ago, when the region began to dry out, eventually assuming the arid environments we see today.
The team identified this climatic turning point after analyzing stalagmites from a cave in Great Basin National Park in Nevada. Stalagmites are pillars of deposited cave drippings that form over hundreds of thousands of years, as water slowly seeps down through the ground, and into caves. A stalagmite’s layers are essentially a record of a region’s moisture over time.
The researchers used a dating technique to determine the ages of certain layers within two stalagmites, then analyzed these layers for chemical signatures of moisture. They dated stalagmite layers ranging from 4,000 to 16,000 years old, observing that moisture content appears to drop dramatically in samples that are less than 8,200 years old.
David McGee, the Kerr-McGee Career Development Assistant Professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says the results suggest that around 8,200 years ago, the climate of the American West began transitioning from a lush landscape to the desert terrain that we know today. On a geological timescale, McGee says the region’s moisture content appears to have dropped rather suddenly—”like falling off a shelf,” he says. This steep drop likely had a dramatic impact on humans living in the region.
“Based upon these data, I would hypothesize that you should see some pretty big changes in how people were living just before and right after 8,000 years ago,” McGee says. “What sort of game were they hunting, what plants were they eating, and where were they choosing to live? Montana’s going to start looking pretty good if the Great Basin is drying out. ”
McGee and graduate students Elena Steponaitis and Alexandra Andrews have published their findings in the journal Quaternary Science Reviews.
Sorting through the stalagmite stacks
McGee and his colleagues concentrated their study on a single cave on the eastern edge of Nevada, known as Lehman Caves, that is part of the Great Basin National Park. A rancher discovered the cave in 1885, and carved a path through its stalagmites, ultimately turning the cave into a tourist attraction. Park rangers have since collected the broken stalagmites, reassembling and storing them in a “library” within the cave.
In 2012, Steponaitis led a group through the cave to look for stalagmites—also known as “speleothems”—that may pinpoint when the western U.S. began to dry out. The researchers formed an assembly line of sorts, methodically labeling and photographing the top and bottom shards of each stalagmite stored in the cave’s library. The group then took these shards into the lab to determine their ages.
To date the shards, the researchers drilled into each stalagmite shard, creating a powder that they then analyzed for isotopes of uranium and thorium. As uranium decays to thorium at a known rate, the ratio of the two isotopes can indicate a layer’s age, or when it first was deposited.
“[Stalagmites] are deposited in layers, kind of like stacked traffic cones,” McGee says. “Each year’s drips make a new coating, and when you cut them open, they have a very clear set of layers, and a clear sense of this is older, this is younger. So they have stratigraphy to them, which is important to us.”
After dating each shard, McGee and Steponaitis singled out two stalagmite samples that were deposited within the last 15,000 years, suggesting these stalagmites were formed toward the end of the last Ice Age. Within each stalagmite, the group dated and marked layers at regular intervals.
Percolating through a cave
To determine the moisture content for each layer, the researchers first examined how water traveled through the cave. They collected drips from various locations throughout the cave, water from standing pools on the cave floor, and soil samples from above the cave.
“I’ve heard stalagmites called ‘fossilized groundwater,’ and that’s essentially what they are,” McGee says. “Groundwater is percolating through the soil and rock, gets to the cave and drips out, and precipitates this stalagmite. The chemistry of that groundwater tells us something about the conditions outside the cave.”
For this particular cave, the researchers observed that the drier the soil above a cave, the slower the percolation of water down into the cave. Water in soil tends to precipitate calcium, leaving more magnesium in the water that reaches the cave. The group analyzed each stalagmite for magnesium, reasoning that the more magnesium found in a particular layer, the drier that period of time was, and vice versa.
Their experiments showed that magnesium levels rose rapidly in layers deposited after roughly 8,200 years ago, indicating that this period experienced a significant drying event. What that event might be is up for debate, although McGee hazards a guess.
“One of the big things that was happening at this time worldwide was the collapse of the last vestiges of this big ice sheet in Canada,” McGee says. “An ice sheet is thought to have important effects on where the jet stream goes. By having this ice sheet here, it made it so the jet stream was more likely to bring storms into the American West, and when it collapsed, the region became more like it is today.”
The team found that lake records from Nevada, Utah, Oregon, and eastern California suggest a similar drying-out period. “Further work will help us figure out exactly what that fingerprint is,” McGee says.
Reference:
“Mid-Holocene drying of the U.S. Great Basin recorded in Nevada speleothems,” Quaternary Science Reviews, Available online 11 June 2015, ISSN 0277-3791, DOI: 10.1016/j.quascirev.2015.04.011
The snake has small ‘hands’ that are approx 1cm long. Credit: Image courtesy of University of Portsmouth
An “absolutely exquisite” fossil of a snake that had four legs has been discovered by a team of scientists and may help show how snakes made the transition from lizards to serpents.
It is the first known fossil of a four-legged snake, and the team — led by Dr Dave Martill from the University of Portsmouth — say that this discovery could help scientists to understand how snakes lost their legs.
The findings were published in the journal Science.
Dr Martill said: “It is generally accepted that snakes evolved from lizards at some point in the distant past. What scientists don’t know yet is when they evolved, why they evolved, and what type of lizard they evolved from. This fossil answers some very important questions, for example it now seems clear to us that snakes evolved from burrowing lizards, not from marine lizards.”
The fossil, from Brazil, dates from the Cretaceous period and is 110 million years old, making it the oldest definitive snake.
Dr Martill discovered the fossil as part of a routine field trip with students to Museum Solnhofen, Germany, a museum that is well-known for its prestige with regard to fossils.
Dr Martill said: “The fossil was part of a larger exhibition of fossils from the Cretaceous period. It was clear that no-one had appreciated its importance, but when I saw it I knew it was an incredibly significant specimen.”
Dr Martill worked with expert German palaeontologist Helmut Tischlinger, who prepared and photographed the specimen, and Dr Nick Longrich from the University of Bath’s Milner Centre for Evolution, who studied the evolutionary relationships of the snake.
Dr Longrich, who had previously worked on snake origins, became intrigued when Martill told him the story over a pint at the local pub in Bath.
He said: “A four-legged snake seemed fantastic and as an evolutionary biologist, just too good to be true, it was especially interesting that it was put on display in a museum where anyone could see it.”
He said he was initially sceptical, but when Dr Martill showed him Tischlinger’s photographs, he knew immediately that it was a fossil snake.
The snake, named Tetrapodophis amplectus by the team, is a juvenile and very small, measuring just 20cm from head to toe, although it may have grown much larger. The head is the size of an adult fingernail, and the smallest tail bone is only a quarter of a millimetre long. But the most remarkable thing about it is the presence of two sets of legs, or a pair of hands and a pair of feet.
The front legs are very small, about 1cm long, but have little elbows and wrists and hands that are just 5mm in length. The back legs are slightly longer and the feet are larger than the hands and could have been used to grasp its prey.
Dr Longrich said: “It is a perfect little snake, except it has these little arms and legs, and they have these strange long fingers and toes.
“The hands and feet are very specialised for grasping. So when snakes stopped walking and started slithering, the legs didn’t just become useless little vestiges — they started using them for something else. We’re not entirely sure what that would be, but they may have been used for grasping prey, or perhaps mates.”
Interestingly, the fossilised snake also has the remains of its last meal in its guts, including some fragments of bone. The prey was probably a salamander, showing that snakes were carnivorous much earlier in evolutionary history than previously believed.
Helmut Tischlinger said: “The preservation of the little snake is absolutely exquisite. The skeleton is fully articulated. Details of the bones are clearly visible and impressions of soft tissues such as scales and the trachea are preserved.”
Tetraphodophis has been categorised as a snake, rather than a lizard, by the team due to a number of features:
The skeleton has a lengthened body, not a long tail.
The tooth implantation, the direction of the teeth, and the pattern of the teeth and the bones of the lower jaw are all snake-like.
The fossil displays hints of a single row of belly scales, a sure fire way to differentiate a snake from a lizard.
Tetrapodophis would have lived on the bank of a salt lake, in an arid scrub environment, surrounded by succulent plants. It would probably have lived on a diet of small amphibians and lizards, trying to avoid the dinosaurs and pterosaurs that lived there.
At the time, South America was united with Africa as part of a supercontinent known as Gondwana. The presence of the oldest definitive snake fossil in Gondwana suggests that snakes may originally have evolved on the ancient supercontinent, and only became widespread much more recently.
Video
An “absolutely exquisite” fossil of a snake that had four legs has been discovered by a team of scientists and may help show how snakes made the transition from lizards to serpents.
Dr Dave Martill from the University of Portsmouth worked with expert German palaeontologist Helmut Tischlinger, and Dr Nick Longrich from the University of Bath’s Milner Centre for Evolution. Dr Dave Martill explains
Reference:
Dave Martill et al. A four-legged snake from the Early Cretaceous of Gondwana. Science, July 2015 DOI: 10.1126/science.aac5672
Mammoth vertebrae in ice, Yukon Territory, Canada. Credit: Kieren Mitchell, University of Adelaide
New research has revealed abrupt warming, that closely resembles the rapid human-made warming occurring today, has repeatedly played a key role in mass extinction events of large animals, the megafauna, in Earth’s past.
Using advances in analysing ancient DNA, radiocarbon dating and other geologic records an international team led by researchers from the University of Adelaide and the University of New South Wales (Australia) have revealed that short, rapid warming events, known as interstadials, recorded during the last ice age or Pleistocene (60,000-12,000 years ago) coincided with major extinction events even before the appearance of man.
Published today in Science, the researchers say by contrast, extreme cold periods, such as the last glacial maximum, do not appear to correspond with these extinctions.
“This abrupt warming had a profound impact on climate that caused marked shifts in global rainfall and vegetation patterns,” said University of Adelaide lead author and Director of the Australian Centre for Ancient DNA, Professor Alan Cooper.
“Even without the presence of humans we saw mass extinctions. When you add the modern addition of human pressures and fragmenting of the environment to the rapid changes brought by global warming, it raises serious concerns about the future of our environment.”
The researchers came to their conclusions after detecting a pattern, 10 years ago, in ancient DNA studies suggesting the rapid disappearance of large species. At first the researchers thought these were related to intense cold snaps.
However, as more fossil-DNA became available from museum specimen collections and through improvements in carbon dating and temperature records that showed better resolution through time, they were surprised to find the opposite. It became increasingly clear that rapid warming, not sudden cold snaps, was the cause of the extinctions during the last glacial maximum.
The research helps explain further the sudden disappearance of mammoths and giant sloths that became extinct around 11,000 years ago at the end of the last ice age.
“It is important to recognize that man still played an important role in the disappearance of the major mega fauna species,” said fellow author Professor Chris Turney from the University of New South Wales.
“The abrupt warming of the climate caused massive changes to the environment that set the extinction events in motion, but the rise of humans applied the coup de grace to a population that was already under stress.”
In addition to the finding, the new statistical methods used to interrogate the datasets (led by Adelaide co-author Professor Corey Bradshaw) and the new data itself has created an extraordinarily precise record of climate change and species movement over the Pleistocene.
This new dataset will allow future researchers a better understanding of this important period than has ever been possible before.
Reference:
Alan Cooper, Chris Turney, Konrad A. Hughen, Barry W. Brook, H. Gregory McDonald, and Corey J. A. Bradshaw. Abrupt warming events drove Late Pleistocene Holarctic megafaunal turnover. Science, 23 July 2015 DOI: 10.1126/science.aac4315
Images showing the back-projected power and path of the Nepal earthquake. Credit: Wenyuan Fan and Peter Shearer
Researchers from Scripps Institution of Oceanography at UC San Diego have accurately mapped out the movement of the devastating 7.8-magnitude Nepal earthquake that killed over 9,000 and injured over 23,000 people. Scientists have determined that the earthquake was a rupture consisting of three different stages. The study could help a rapidly growing region understand its future seismic risks.
The Himalayan region is particularly prone to earthquakes and this study will serve as an important benchmark for understanding where future earthquakes may occur, especially since the area has experienced high population growth over the past few decades.
The study assessed the presence of low frequency and high frequency waves over the three stages of the earthquake. High frequency waves cause more shaking, thereby posing the greatest risks for structural damages. Low frequency waves are less violent and less damaging to buildings and infrastructure.
“The Nepal earthquake is a warning sign that the region is of high seismic risk, and each earthquake behaves differently. Some earthquakes jump from one fault line to another, whereas the Nepal quake apparently occurred on the same fault line in three different stages, moving eastward,” said Scripps geophysicist Peter Shearer, “Using this research, we can better understand and identify areas of high seismic hazard in the region.”
This first peer-reviewed study on the April 2015 earthquake in Nepal, “Detailed rupture imaging of the 25 April 2015 Nepal earthquake using teleseismic P waves” was published online July 16 in the American Geophysical Union (AGU) journal Geophysical Research Letters.
Using the Global Seismic Network (GSN), Shearer and Scripps graduate student Wenyuan Fan were able to unravel the complex evolution of fault slips during this earthquake. The study concludes that the rupture traveled mostly eastward and occurred in three distinct stages; Stage 1 was weak and slow; Stage 2 was near Kathmandu and had the greatest slip but was relatively deficient in high-frequency radiation; and Stage 3 was relatively slow as well. Overall, this earthquake was more complicated, with multi-stage movements on multiple faults, than smooth models of continuous rupture on a single fault plane.
“Using the GSN instead of regional array data really enhanced the spatial resolution of the back-projection images and helped us see that frequency-dependent rupture was one of the main features of this earthquake,” said Fan. “Stage 2 was high-frequency-deficient and occurred closest to Kathmandu, which was probably why ground shaking was less severer than expected for such a high-magnitude earthquake.”
The Global Seismic Network provides high-quality broadband digital seismic data for monitoring earthquakes and learning about Earth structure. A precursor to this network was initiated by Scripps researchers in the 1960s and is still in use today. Scripps currently operates one-third of the 153 global seismometers of the GSN. Fan and Shearer used the GSN data because they are open-source (available to anyone), have good coverage of the Nepal region, and have a long history of reliable recordings.
“In general, understanding large earthquakes will inform our ability to forecast the nature of future earthquakes,” said Shearer.
Shearer and Fan hope to use the same methodology to study other large, global earthquakes from the past decade to provide a broader picture of earthquake behavior and help in predicting ground shaking for future events.
Reference:
Wenyuan Fan, Peter M. Shearer. Detailed rupture imaging of the 25 April 2015 Nepal earthquake using teleseismicPwaves. Geophysical Research Letters, 2015; DOI: 10.1002/2015GL064587
A gigantic sunspot almost 130,000 km across captured by NASA’s Solar Dynamic Observatory on October 23, 2014. Credit: NASA/SD
This month there’s been a hoopla about a mini ice age, and unfortunately it tells us more about failures of science communication than the climate. Such failures can maintain the illusion of doubt and uncertainty, even when there’s a scientific consensus that the world is warming.
The story starts benignly with a peer-reviewed paper and a presentation in early July by Professor Valentina Zharkova, from Northumbria University, at Britain’s National Astronomy Meeting.
The paper presents a model for the sun’s magnetic field and sunspots, which predicts a 60% fall in sunspot numbers when extrapolated to the 2030s. Crucially, the paper makes no mention of climate.
The first failure of science communication is present in the Royal Astronomical Society press release from July 9. It says that “solar activity will fall by 60 per cent during the 2030s” without clarifying that this “solar activity” refers to a fall in the number of sunspots, not a dramatic fall in the life-sustaining light emitted by the sun.
The press release also omits crucial details. It does say that the drop in sunspots may resemble the Maunder minimum, a 17th century lull in solar activity, and includes a link to the Wikipedia article on the subject. The press release also notes that the Maunder minimum coincided with a mini ice age.
But that mini ice age began before the Maunder minimum and may have had multiple causes, including volcanism.
Crucially, the press release doesn’t say what the implications of a future Maunder minimum are for climate.
Filling in the gaps
How would a new Maunder minimum impact climate? It’s an obvious question, and one that climate scientists have already answered. But many journalists didn’t ask the experts, instead drawing their own conclusions.
The UK’s Telegraph warned:
[…] the earth is 15 years from a mini ice age that will cause bitterly cold winters during which rivers such as the Thames freeze over.
Pictures of glaciers and frozen rivers loomed large.
News Corp’s Andrew Bolt used the mini ice age to attack climate science. Many climate sceptic bloggers readily accepted the story, despite climate never being mentioned in the peer-reviewed paper.
The media failed in its duty to investigate and inform. It didn’t seek expert comment to put the research into context. Instead journalists tried to answer technical climate science questions themselves, and mostly got it wrong.
As discussed previously, the impact of a new Maunder minimum on climate has beenstudied many times. There’s 40% more CO2 in the air now than during the 17th century, and global temperature records are being smashed. A new Maunder minimum would slow climate change, but it is not enough to stop it.
The scientist at the centre of the media storm, Valentina Zharkova, told USA today:
In the press release, we didn’t say anything about climate change. My guess is when they heard about Maunder minimum, they used Wikipedia or something to find out more about it.
Mixed messages
While Zharkova was surprised by the media coverage, she and others continued to discuss a new mini ice age.
If a mini ice age is at odds with the prior literature, why does Zharkova continue speculating about it? In personal correspondence with Zharkova, she told me it was only after the media coverage that her research was connected to climate change and the Maunder minimum. However, she said that once the connection was made, it did make sense to her.
Zharkova also told IFLS: We didn’t mention anything about the weather change, but I would have to agree that possibly you can expect it [a mini ice age].
So it seems Zharkova’s justification is based on media extrapolation of her own press release and Wikipedia, not the extensive peer-reviewed literature on the Maunder minimum itself.
I emailed Zharkova and she sent me two studies that support her views, but they aren’t representative of the literature and I don’t believe she has critically evaluated their content.
Is there any quantitative basis for claims of a mini ice age? Zharkova and her colleagues have cited a 1997 article by Judith Lean, who showed the sun’s brightness (quantified by solar irradiance) was 3 W per m2 less during the Maunder minimum than today. More recent studies, including those by Lean, find the solar irradiance varies less than was thought in 1997.
In plain English, the small change in sunlight reaching the Earth during a new Maunder minimum wouldn’t be enough to reverse climate change. For the technically minded, even a 3 W per m2 change in irradiance corresponds to a radiative forcing of just 0.5 W per m2 (because the Earth is a sphere and not a flat circle), which is less than the radiative forcing produced by anthropogenic greenhouse gases.
To be blunt: no mini ice age for us. The real story of the impending mini ice age isn’t about climate at all. It is a cautionary tale, of how science should and shouldn’t be communicated.
The lessons to be learned from this is scientists must communicate their science concisely and accurately, especially if we are to avoid the media frenzy highlighted by the ABC’s Media Watch. If scientists, science organisations and media aren’t careful, they can inadvertently end up promoting dangerous misinformation.
Note: The above post is reprinted from materials provided by The Conversation. This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).The Conversation
Research by University of Reading scientists into climatic patterns from the past 1,000 years has improved our understanding of how the weather in Europe could respond to changes in the future.
In a letter published in Nature, Dr Pablo Ortega from the National Centre for Atmospheric Science (NCAS), based in the University of Reading’s Department of Meteorology, and other European colleagues present an unprecedented annually resolved reconstruction of the NAO evolution during the past millennium.
The North Atlantic Oscillation (NAO) describes a seesaw in atmospheric pressure between the regions of the Azores High and the Icelandic Low that controls the flow of winter storms across the Atlantic. It has therefore large impacts on winter climate temperature over Europe.
When the difference in pressure between Azores and Iceland is stronger than normal the NAO enters a positive phase and Atlantic storms are directed towards the British Isles and Northern Europe, carrying precipitation and warmer temperatures, and keep the Mediterranean region on the dry side.
Climate prediction
Recent developments in climate models offer promise to predict the NAO evolution and therefore the climate over Europe from one season to another. However, the lack of long direct observations prevents the assessment of its predictability at longer lead times (years to decades).
This latest reconstruction, carried out at Dr Ortega’s previous institution the LSCE/CEA (France), relies on the combination and analysis of climate information from 48 different natural archives or “proxies” distributed around the Atlantic Ocean, including tree rings, speleothems, ice cores and lake sediments.
The final reconstruction indicates that the NAO phase was predominantly positive during the 13th and 14th centuries, but not during the whole medieval period as a previous analysis suggested to explain the unusually warm temperatures in Northern Europe at the time. This former analysis, based only on two natural archives, is also debated by other documentary sources in Europe. To further support their findings, Dr Ortega and colleagues have mimicked and compared both reconstruction approaches in climate simulations with six different state-of-the-art climate models. Their analysis is conclusive; all the models support the new reconstruction as a more reliable estimation of past NAO variability.
“This validation with models is a novel encouraging approach for the paleoclimatology community”, Dr Ortega explains.
“Up to now, natural archives have been used to assess the ability of climate models to reproduce past climate variability. Our study has shown the added value of using models to test the reliability of paleoclimate reconstructions.”
Another important result, with implications for climate prediction over Europe, is the identification of a systematic NAO response to volcanic eruptions. In the reconstruction, positive NAO phases emerge two years after strong volcanic eruptions, consistent with satellite observations for the Mt Pinatubo eruption in the Philippines.
Reference:
“A model-tested North Atlantic Oscillation reconstruction for the past millennium.” Nature 523, 71–74 (02 July 2015) DOI: 10.1038/nature14518
A variety of deltas: the Mississippi birdfoot delta (right) and Mexico’s Grijalva cuspate delta (left). Credit: NASA Landsat
The Mississippi River delta is a rich ecosystem of barrier islands, estuaries, and wetlands that’s home to a diverse mix of wildlife—as well as more than 2 million people. Over the past few decades, the shape of the delta has changed significantly, as ocean waves have carved away at the coastline, submerging and shrinking habitats.
To keep flooding at bay, engineers have erected dams and levees along the river. However, it’s unclear how such protective measures will affect the shape of the river delta, and its communities, over time.
Now researchers from MIT and the Woods Hole Oceanographic Institution (WHOI) have devised a simple way to predict a river delta’s shape, given two competing factors: its river’s force in depositing sediment into the ocean, and ocean waves’ strength in pushing that sediment back along the coast. Depending on the balance of the two, the coastline of a river delta may take on a smooth “cuspate” shape, or a more pointed “crenulated” outline, resembling a bird’s foot.
The new metric may help engineers determine how the shape of a delta, such as the Mississippi’s, may shift in response to engineered structures such as dams and levees, and environmental changes, such as hurricane activity and sea-level rise.
Jaap Nienhuis, a graduate student in the MIT-WHOI Joint Program in Marine Geology and Geophysics, says the effects of climate change, and the human efforts to combat these effects, are already making an impact on river deltas around the world.
“Because there are so many people living on a river delta, you want to know what its morphology or shape will look like in the future,” Nienhuis says. “For the Mississippi, the river supplies a lot of sediment. But because there are a lot of dams on the Mississippi nowadays, there is not as much sand coming down the river, so people are very worried about how this delta will evolve, especially with sea-level rise, over the coming centuries.”
Nienhuis, and Andrew Ashton and Liviu Glosan of WHOI, report their results in the journal Geology.
Shaping a shoreline
Over hundreds of thousands of years, a river’s sand and silt flow toward the coast, ultimately piling up at a river’s mouth in the form of a low-lying delta. A delta’s coastline can be relatively smooth, with most sand depositing from the main river, or it can fan out in the shape of a bird’s foot, as the river bifurcates into tributaries and channels, each of which deposits sand in finger-like projections.
Scientists often characterize a delta as either river-dominated or wave-dominated.
In a wave-dominated delta, such as the Nile River delta in Egypt, incoming ocean waves are stronger than the river’s flow. As a result, waves push outflowing sediment back along the coast, effectively smoothing the coastline. By contrast, a river-dominated delta, such as the Mississippi’s, is shaped by a stronger river, which deposits sand faster than ocean waves can push back, creating a crenulated coastline.
While this relationship between rivers and ocean waves is generally understood, Nienhuis says there is no formal way to determine when a delta will tip toward a smooth or pointy shape.
The researchers came up with a simple ratio to predict a delta’s shape, based on a river’s sediment flux, or the flow rate of sediment through a river, and the strength of ocean waves, determined by a wave’s height, frequency, and angle of approach.
Based on the various factors that determine the overall ratio, the team determined the point at which a delta would no longer be a smooth outline, shaped by ocean waves, but instead, a pointy coastline, influenced more by the river.
“At some point there’s so much sediment that you exceed the maximum of what waves can do,” Nienhuis says, “and then you become a ‘bird foot,’ or river-dominated delta, because the river is so much stronger.”
A delta’s tipping point
Nienhuis and his colleagues applied the new method to 25 river deltas on the north shore of the Indonesian island of Java, a region where sediments have deposited on a shallow continental shelf, creating a wide variety of delta shapes.
For each delta, the team used a global wave model developed by the National Oceanic and Atmospheric Administration to determine the height, frequency, and direction of each incoming wave. The researchers also used a model to determine the corresponding river’s sediment flux.
Using data from both models, Nienhuis determined the ratio of river-to-ocean wave strength for each delta, and found that those deltas with a ratio greater than or equal to 1 were more likely to have multiple river channels, with deltas that project out from the shoreline. The main factor determining this transition turned out to be the angle at which ocean waves generally approach the coast: If the angle of approach is 45 degrees or greater, then ocean waves are no longer able to smooth out the amount of sediment coming from a river, tipping a delta’s shape toward a river-dominated morphology.
Nienhuis says the group’s method may help engineers predict the shape a delta may take if erected dams or levees change a river’s sediment flow. Similarly, the method may estimate the evolution of deltas with climate change, as rising sea levels and increased hurricane activity will likely alter the behavior and magnitude of ocean waves.
Douglas Edmonds, an assistant professor of geological sciences at Indiana University who was not involved in the research, says the new model “is a powerful advance, because it allows engineers and environmental managers to make informed predictions about how to restore deltas that are drowning. For example, in places like coastal Louisiana, substantial funds are needed to divert water and sediment from rivers into drowning areas to build new deltaic land. To make sure these diversions are successful, we need to predict how that new deltaic land will evolve. Nienhuis et al. have provided an important blueprint toward that end.”
Reference:
“What makes a delta wave-dominated?” Geology, June 2015, v. 43, p. 511-514, first published on April 27, 2015, DOI: 10.1130/G36518.1
Compared to its celestial neighbours Venus and Mars, Earth is a pretty habitable place. So how did we get so lucky? A new study sheds light on the improbable evolutionary path that enabled Earth to sustain life.
The research, published this week in Nature Geoscience, suggests that Earth’s first crust, which was rich in radioactive heat-producing elements such as uranium and potassium, was torn from the planet and lost to space when asteroids bombarded the planet early in its history. This phenomenon, known as impact erosion, helps explain a landmark discovery made over a decade ago about the Earth’s composition.
Researchers with the University of British Columbia and University of California, Santa Barbara say that the early loss of these two elements ultimately determined the evolution of Earth’s plate tectonics, magnetic field and climate.
“The events that define the early formation and bulk composition of Earth govern, in part, the subsequent tectonic, magnetic and climatic histories of our planet, all of which have to work together to create the Earth in which we live,” said Mark Jellinek, a professor in the Department of Earth, Ocean & Atmospheric Sciences at UBC. “It’s these events that potentially differentiate Earth from other planets.”
On Earth, shifting tectonic plates cause regular overturning of Earth’s surface, which steadily cools the underlying mantle, maintains the planet’s strong magnetic field and stimulates volcanic activity. Erupting volcanoes release greenhouse gases from deep inside the planet and regular eruptions help to maintain the habitable climate that distinguishes Earth from all other rocky planets.
Venus is the most similar planet to Earth in terms of size, mass, density, gravity and composition. While Earth has had a stable and habitable climate over geological time, Venus is in a climate catastrophe with a thick carbon dioxide atmosphere and surface temperatures reaching about 470 C. In this study, Jellinek and Matt Jackson, an associate professor at the University of California, explain why the two planets could have evolved so differently.
“Earth could have easily ended up like present day Venus,” said Jellinek. “A key difference that can tip the balance, however, may be differing extents of impact erosion.”
With less impact erosion, Venus would cool episodically with catastrophic swings in the intensity of volcanic activity driving dramatic and billion-year-long swings in climate.
“We played out this impact erosion story forward in time and we were able to show that the effect of the conditions governing the initial composition of a planet can have profound consequences for its evolution. It’s a very special set of circumstances that make Earth.”
Reference:
A. M. Jellinek, M. G. Jackson. Connections between the bulk composition, geodynamics and habitability of Earth. Nature Geoscience, 2015; DOI: 10.1038/ngeo2488
