Researchers find new information about ‘Snowball Earth’ period

It is rather difficult to imagine, but approximately 635 million years ago, ice may have covered a vast portion of our planet in an event called “Snowball Earth.” According to the Snowball Earth hypothesis, the massive ice age that occurred before animal life appeared, when Earth’s landmasses were most likely clustered near the equator, precipitated relatively rapid changes in atmospheric conditions and a subsequent greenhouse heat wave. This particular period of extensive glaciation and subsequent climate changes might have supplied the cataclysmic event that gave rise to modern levels of atmospheric oxygen, paving the way for the rise of animals and the diversification of life during the later Cambrian explosion.

But if ice covered the earth all the way to the tropics during what is known as the Marinoan glaciation, how did the planet spring back from the brink of an ice apocalypse? Huiming Bao, Charles L. Jones Professor in Geology & Geophysics at LSU, might have some of the answers. Bao and LSU graduate students Bryan Killingsworth and Justin Hayles, together with Chuanming Zhou, a colleague at Chinese Academy of Sciences, had an article published on Feb. 5 in the Proceedings of the National Academy of Sciences, or PNAS, that provides new clues on the duration of what was a significant change in atmospheric conditions following the Marinoan glaciation.

“The story is to put a time limit on how fast our Earth system can recover from a total frozen state,” Bao said. “It is about a unique and rapidly changing post-glacial world, but is also about the incredible resilience of life and life’s remarkable ability to restore a new balance between atmosphere, hydrosphere and biosphere after a global glaciation.”

Bao’s group went about investigating the post-glaciation period of Snowball Earth by looking at unique occurrences of “crystal fans” of a common mineral known as barite (BaSO4), deposited in rocks following the Marinoan glaciation. Out of the three stable isotopes of oxygen, O-16, O-17 and O-18, Bao’s group pays close attention to the relatively scarce isotope O-17. According to Killingsworth, there aren’t many phenomena on earth that can change the normally expected ratio of the scare isotope O-17 to more abundant isotope O-18. However, in sulfate minerals such as barite in rock samples from around 635 million years ago, Bao’s group finds large deviations in the normal ratio of O-17 to O-18 with respect to O-16 isotopes.

“If something unusual happens with the composition of the atmosphere, the oxygen isotope ratios can change,” Killingsworth said. “We see a large deviation in this ratio in minerals deposited around 635 million years ago. This occurred during an extremely odd time in atmospheric history.”

According to Bao’s group, the odd oxygen isotope ratios they find in barite samples from 635 million years ago could have occurred if, following the extensive Snowball Earth glaciation, Earth’s atmosphere had very high levels of carbon dioxide, or CO2. An ultra-high carbon dioxide atmosphere, Killingsworth explains, where CO2 levels match levels of atmospheric oxygen, would grab more O-17 from oxygen. This would cause a depletion of the O-17 isotope in air and subsequently in barite minerals, which incorporate oxygen as they grow. Bao’s group has found worldwide deposits of this O-17 depleted sulfate mineral in rocks dating from the global glaciation event 635 million years ago, indicating an episode of an ultra-high carbon dioxide atmosphere following the Marinoan glaciation.

“Something significant happened in the atmosphere,” Killingsworth said. “This kind of an atmospheric shift in carbon dioxide is not observed during any other period of Earth’s history. And now we have sedimentary rock evidence for how long this ultra-high carbon dioxide period lasted.”

By using available radiometric dates from areas near layers of barite deposits, Bao’s group has been able to come up with an estimate for the duration of what is now called the Marinoan Oxygen-17 Depletion, or MOSD, event. Bao’s group estimates the MOSD duration at 0 – 1 million years.

“This is, so far, really the best estimate we could get from geological records, in line with previous models of how long an ultra-high carbon dioxide event could last before the carbon dioxide in the air would get drawn back into the oceans and sediments,” Killingsworth said.

Normally, carbon dioxide levels in the atmosphere are in balance with levels of carbon dioxide in the ocean. However, if water and air were cut off by a thick layer of ice during Snowball Earth, atmospheric carbon dioxide levels could have increased drastically. In a phenomenon similar to the climate change Earth is witnessing in modern times, high levels of atmospheric carbon dioxide would have created a greenhouse gas warming effect, trapping heat inside the planet’s atmosphere and melting the Marinoan ice. Essentially, the Marinoan glaciation created the potential for extreme changes in atmospheric chemistry that in turn lead to the end of Snowball Earth and the beginning of a new explosion of animal life on Earth.

While previous work by Bao’s group had advanced the interpretation of the strange occurrence of O-17 depleted barite just after the Marinoan glaciation, there was still much uncertainty on the duration of ultra-high CO2 levels after meltdown of Snowball Earth. Bao’s discovery of a field site with many barite layers gave the opportunity to track how oxygen isotope ratios changed through a thickness of sedimentary rock. As the pages in a novel can be thought of as representing time, so layers of sedimentary rock represent geological history. However, these rock “pages” represented an unknown duration of time for the MOSD event. By using characteristic features of the Marinoan rock sequence occurring regionally in South China, Bao’s group linked the barite layer site to other sites in the region that did have precise dates from volcanic ash beds. Bao’s group has succeeded in estimating the duration of the MOSD event, and thus the time it took for Earth to restore “normal” CO2 levels in the atmosphere.

“To some extent, our findings demonstrate that whatever happens to Earth, she will recover, and recover at a rapid pace,” Bao said. “Mother Earth lived and life carried on even in the most devastating situation. The only difference is the life composition afterwards. In other words, whatever humans do to the Earth, life will go on. The only uncertainty is whether humans will still remain part of the life composition.”

Bao says that he had been interested in this most intriguing episode of Earth’s history since Paul Hoffman, Dan Schrag and colleagues revived the Snowball Earth hypothesis in 1998.

“I was a casual ‘non-believer’ of this hypothesis because of the mere improbability of such an Earth state,” Bao said. “There was nothing rational or logic in that belief for me, of course. I remember I even told my job interviewers back in 2000 that one of my future research plans was to prove that the Snowball Earth hypothesis was wrong.”

However, during a winter break in 2006, Bao obtained some unusual data from barite, a sulfate mineral dating from the Snowball Earth period that he received from a colleague in China.

“I started to develop my own method to explore this utterly strange world,” Bao said. “Now, it seems that our LSU group is the one offering the strongest supporting evidence for a ‘Snowball Earth’ back 635 million years ago. I certainly did not see this coming. The finding we published in 2008 demonstrates, again, that new scientific breakthroughs are often brought in by outsiders.”

Bao credits his research ideas, analytical work and pleasure of working on this project to his two graduate students, Killingsworth and Hayles, as well as his long-time Chinese collaborators. Bao brought Killingsworth and Hayles to an interior mountainous region in South China in December 2011, where the group succeeded in finding multiple barite layers in a section of rocks dating to 635 million years ago. This discovery formed a large part of their analysis and subsequent publication in PNAS.

“Nothing can beat the intellectual excitement and satisfaction you get from research in the field and in the laboratory,” Bao said.

Volcano location could be greenhouse-icehouse key

This is Cin-Ty Lee. -  Rice University
This is Cin-Ty Lee. – Rice University

A new Rice University-led study finds the real estate mantra “location, location, location” may also explain one of Earth’s enduring climate mysteries. The study suggests that Earth’s repeated flip-flopping between greenhouse and icehouse states over the past 500 million years may have been driven by the episodic flare-up of volcanoes at key locations where enormous amounts of carbon dioxide are poised for release into the atmosphere.

“We found that Earth’s continents serve as enormous ‘carbonate capacitors,'” said Rice’s Cin-Ty Lee, the lead author of the study in this month’s GeoSphere. “Continents store massive amounts of carbon dioxide in sedimentary carbonates like limestone and marble, and it appears that these reservoirs are tapped from time to time by volcanoes, which release large amounts of carbon dioxide into the atmosphere.”

Lee said as much as 44 percent of carbonates by weight is carbon dioxide. Under most circumstances that carbon stays locked inside Earth’s rigid continental crust.

“One process that can release carbon dioxide from these carbonates is interaction with magma,” he said. “But that rarely happens on Earth today because most volcanoes are located on island arcs, tectonic plate boundaries that don’t contain continental crust.”

Earth’s climate continually cycles between greenhouse and icehouse states, which each last on timescales of 10 million to 100 million years. Icehouse states — like the one Earth has been in for the past 50 million years — are marked by ice at the poles and periods of glacial activity. By contrast, the warmer greenhouse states are marked by increased carbon dioxide in the atmosphere and by an ice-free surface, even at the poles. The last greenhouse period lasted about 50 million to 70 million years and spanned the late Cretaceous, when dinosaurs roamed, and the early Paleogene, when mammals began to diversify.

Lee and colleagues found that the planet’s greenhouse-icehouse oscillations are a natural consequence of plate tectonics. The research showed that tectonic activity drives an episodic flare-up of volcanoes along continental arcs, particularly during periods when oceans are forming and continents are breaking apart. The continental arc volcanoes that arise during these periods are located on the edges of continents, and the magma that rises through the volcanoes releases enormous quantities of carbon dioxide as it passes through layers of carbonates in the continental crust.

Lee, professor of Earth science at Rice, led the four-year study, which was co-authored by three Rice faculty members and additional colleagues at the University of Tokyo, the University of British Columbia, the California Institute of Technology, Texas A&M University and Pomona College.

Lee said the study breaks with conventional theories about greenhouse and icehouse periods.

“The standard view of the greenhouse state is that you draw carbon dioxide from the deep Earth interior by a combination of more activity along the mid-ocean ridges — where tectonic plates spread — and massive breakouts of lava called ‘large igneous provinces,'” Lee said. “Though both of these would produce more carbon dioxide, it is not clear if these processes alone could sustain the atmospheric carbon dioxide that we find in the fossil record during past greenhouses.”

Lee is a petrologist and geochemist whose research interests include the formation and evolution of continents as well as the connections between deep Earth and its oceans and atmosphere..

Lee said the conclusions in the study developed over several years, but the initial idea of the research dates to an informal chalkboard-only seminar at Rice in 2008. The talk was given by Rice oceanographer and study co-author Jerry Dickens, a paleoclimate expert; Lee and Rice geodynamicist Adrian Lenardic, another co-author, were in the audience.

“Jerry was talking about seawater in the Cretaceous, and he mentioned that 93.5 million years ago there was a mass extinction of deepwater organisms that coincided with a global marine anoxic event — that is, the deep oceans became starved of oxygen,” Lee said. “Jerry was talking about the impact of anoxic conditions on the biogeochemical cycles of trace metals in the ocean, but I don’t remember much else that he said that day because it had dawned on me that 93 million years ago was a very interesting time for North America. There was a huge flare-up of volcanism along the western margin of North America, and the peak of all this activity was 93 million years ago.

“I thought, ‘Wow!'” Lee recalled. “I know coincidence doesn’t mean causality, but it certainly got me thinking. I decided to look at whether the flare-up in volcanic activity that helped create the Sierra Nevada Mountains may also have affected Earth’s climate.”

Over the next two years, Lee developed the idea that continental-arc volcanoes could pump carbon dioxide into the atmosphere. One indicator was evidence from Mount Etna in Sicily, one of the few active continental-arc volcanoes in the world today. Etna produces large amounts of carbon dioxide, Lee said, so much that it is often considered an outlier in global averages of modern volcanic carbon dioxide production.

Tectonic and petrological evidence indicated that many Etna-like volcanoes existed during the Cretaceous greenhouse, Lee said. He and colleagues traced the likely areas of occurrence by looking for tungsten-rich minerals like scheelite, which are formed on the margins of volcanic magma chambers when magma reacts with carbonates. It wasn’t easy; Lee spent an entire year pouring through World War II mining surveys from the western U.S. and Canada, for example.

“There is evidence to support our idea, both in the geological record and in geophysical models, the latter of which show plausibility,” he said. For example, in a companion paper published last year in G-Cubed, Lenardic used numerical models that showed the opening and breakup of continents could change the nature of subduction zones, generating oscillations between continental- and island-arc dominated states.

Though the idea in the GeoSpheres study is still a theory, Lee said, it has some advantages over more established theories because it can explain how the same basic set of geophysical conditions could produce and sustain a greenhouse or an icehouse for many millions of years.

“The length of subduction zones and the number of arc volcanoes globally don’t have to change,” Lee said. “But the nature of the arcs themselves, whether they are continental or oceanic, does change. It is in the continental-arc stage that CO2 is released from an ever-growing reservoir of carbonates within the continents.”

Visiting snowball Earth

Ancient glacial deposits in Norway (snowball Earth-aged Smalfjord and the younger Mortensnes formations) are superbly documented and illustrated in this comprehensive eight-day field guide. This guide was written specifically for use in the field, and, as authors A.H.N. Rice, Marc B. Edwards, and T.A. Hansen note, “is not necessarily fully understandable without actually being in front of the rocks.” However, all readers will find the guide a fascinating peek into a wondrous, ancient Snowball Earth.

The aim of the authors (A.H.N. Rice from the University of Vienna; Marc B. Edwards of Houston, Texas, USA; and T.A. Hansen of Talisman Energy Norge AS) is to provide detailed coverage of both the typical and the atypical lithologies and sedimentary structures in the glacial deposits in Finnmark, northern Norway. The guide, they note, is not a systematic update on published ideas and interpretations, although this has been done at some outcrops. Instead, the authors invite readers “to critically evaluate our interpretations in the field and to publish their own ideas.”

The area is a treasure-trove of geologic features. Lodgement, banded, deformation, flow and melt-out diamictites derived from gneissic, clastic, and dolomitic sources are described, as well as glaciomarine, proglacial and fluvioglacial sediments. Outcrops showing glaciotectonic folds, faults, flanking structures, shear-sense criteria (sigma-clasts), fluidized sediments, pro- and sub-glacial channels, iceberg dump structures, ghost clasts, dropstones, ice-crystal molds, and a kettle-hole are included. The classic glacial striations at Oaibaččanjar’ga are described in detail. Marinoan cap-dolostones overlying the Smalford Formation are also included. More than 60 illustrations complete this guide.

Logistically, Finnmark is easily accessible by airplane and/or car in comparison to other Neoproterozoic glacial successions. Most outcrops are along the roadside or are easily reached by small boats. The book includes information about accommodations and renting small boats, as well as a summary of the natural and local history.

Finnmark lies well north of the Arctic Circle and thus has 24 hours of daylight during the midsummer months. The midnight sun disappears around 28 July in the Tana area, although it remains light throughout the night for a week or more afterward. However, nighttime temperatures rapidly drop in August, and a ground frost is not unusual in the first week of that month. Better weather is more likely in late June to early July, and this is the recommended time for an excursion.

This excursion was first run as part of the International GeoscienceProgramme (IGCP) 512 “Neoproterozoic Ice Ages” project during the 33rd International Geological Congress, in Oslo, Norway, in 2008.

What really happened prior to ‘Snowball Earth’?

<IMG SRC="/Images/366405725.jpg" WIDTH="350" HEIGHT="233" BORDER="0" ALT="In a study published in the January 2012 issue of Geology, Swart suggests that the large changes in the carbon isotopic composition of carbonates which occurred prior to the major climatic event more than 500 million years ago, known as ‘Snowball Earth,’ are unrelated to worldwide glacial events. – UM/RSMAS”>
In a study published in the January 2012 issue of Geology, Swart suggests that the large changes in the carbon isotopic composition of carbonates which occurred prior to the major climatic event more than 500 million years ago, known as ‘Snowball Earth,’ are unrelated to worldwide glacial events. – UM/RSMAS

In a study published in the journal Geology, scientists at the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science suggest that the large changes in the carbon isotopic composition of carbonates which occurred prior to the major climatic event more than 500 million years ago, known as ‘Snowball Earth,’ are unrelated to worldwide glacial events.

“Our study suggests that the geochemical record documented in rocks prior to the Marinoan glaciation or ‘Snowball Earth’ are unrelated to the glaciation itself,” said UM Rosenstiel professor Peter Swart, a co-author of the study. “Instead the changes in the carbon isotopic ratio are related to alteration by freshwater as sea level fell.”

In order to better understand the environmental conditions prior to ‘Snowball Earth’, the research team analyzed geochemical signatures preserved in carbonate rock cores from similar climactic events that happened more recently – two million years ago – during the Pliocene-Pleistocene period.

The team analyzed the ratio of the rare isotope of carbon (13C) to the more abundant carbon isotope (12C) from cores drilled in the Bahamas and the Enewetak Atoll in the Pacific Ocean. The geochemical patterns that were observed in these cores were nearly identical to the pattern seen prior to the Marinoan glaciation, which suggests that the alteration of rocks by water, a process known as diagenesis, is the source of the changes seen during that time period.

Prior to this study, scientists theorized that large changes in the cycling of carbon between the organic and inorganic reservoirs occurred in the atmosphere and oceans, setting the stage for the global glacial event known as ‘Snowball Earth’.

“It is widely accepted that changes in the carbon isotopic ratio during the Pliocene-Pleistocene time are the result of alteration of rocks by freshwater,” said Swart. “We believe this is also what occurred during the Neoproterozoic. Instead of being related to massive and complicated changes in the carbon cycle, the variations seen in the Neoproterozoic can be explained by simple process which we understand very well.”

Scientists acknowledge that multiple sea level fluctuations occurred during the Pliocene-Pleistocene glaciations resulting from water being locked up in glaciers. Similar sea-level changes during the Neoproterozoic caused the variations in the global carbon isotopic signal preserved in the older rocks, not a change in the distribution of carbon as had been widely postulated.

Team debunks theory on end of ‘Snowball Earth’ ice age

Crystals of highly carbon-13-depleted carbonate are observed using a light microscope. -  Thomas Bristow
Crystals of highly carbon-13-depleted carbonate are observed using a light microscope. – Thomas Bristow

There’s a theory about how the Marinoan ice age-also known as the “Snowball Earth” ice age because of its extreme low temperatures-came to an abrupt end some 600 million years ago. It has to do with large amounts of methane, a strong greenhouse gas, bubbling up through ocean sediments and from beneath the permafrost and heating the atmosphere.

The main physical evidence behind this theory has been samples of cap dolostone from south China, which were known to have a lot less of the carbon-13 isotope than is normally found in these types of carbonate rocks. (Dolostone is a type of sedimentary rock composed of the carbonate mineral, dolomite; it’s called cap dolostone when it overlies a glacial deposit.) The idea was that these rocks formed when Earth-warming methane bubbled up from below and was oxidized-“eaten”-by microbes, with its carbon wastes being incorporated into the dolostone, thereby leaving a signal of what had happened to end the ice age. The idea made sense, because methane also tends to be low in carbon-13; if carbon-13-depeleted methane had been made into rock, that rock would indeed also be low in carbon-13. But the idea was controversial, too, since there had been no previous isotopic evidence in carbonate rock of methane-munching microbes that early in Earth’s history.

And, as a team of scientists led by researchers from the California Institute of Technology (Caltech) report in this week’s issue of the journal Nature, it was also wrong-at least as far as the geologic evidence they looked at goes. Their testing shows that the rocks on which much of that ice-age-ending theory was based were formed millions of years after the ice age ended, and were formed at temperatures so high there could have been no living creatures associated with them.

“Our findings show that what happened in these rocks happened at very high temperatures, and abiologically,” says John Eiler, the Robert P. Sharp Professor of Geology and professor of geochemistry at Caltech, and one of the paper’s authors. “There is no evidence here that microbes ate methane as food. The story you see in this rock is not a story about ice ages.”

To tell the rocks’ story, the team used a technique Eiler developed at Caltech that looks at the way in which rare isotopes (like the carbon-13 in the dolostone) group, or “clump,” together in crystalline structures like bone or rock. This clumping, it turns out, is highly dependent upon the temperature of the immediate environment in which the crystals form. Hot temperatures mean less clumping; low temperatures mean more.

“The rocks that we analyzed for this study have been worked on before,” says Thomas Bristow, the paper’s first author and a former postdoc at Caltech who is now at NASA Ames Research Center, “but the unique advance available and developed at Caltech is the technique of using carbonate clumped-isotopic thermometry to study the temperature of crystallization of the samples. It was primarily this technique that brought new insights regarding the geological history of the rocks.”

What the team’s thermometer made very clear, says Eiler, is that “the carbon source was not oxidized and turned into carbonate at Earth’s surface. This was happening in a very hot hydrothermal environment, underground.”

In addition, he says, “We know it happened at least millions of years after the ice age ended, and probably tens of millions. Which means that whatever the source of carbon was, it wasn’t related to the end of the ice age.”

Since this rock had been the only carbon-isotopic evidence of a Precambrian methane seep, these findings bring up a number of questions-questions not just about how the Marinoan ice age ended, but about Earth’s budget of methane and the biogeochemistry of the ocean.

“The next stage of the research is to delve deeper into the question of why carbon-13-depleted carbonate rocks that formed at methane seeps seem to only be found during the later 400 million years of Earth history,” says John Grotzinger, the Fletcher Jones Professor of Geology at Caltech and the principal investigator on the work described. “It is an interesting fact of the geologic record that, despite a well-preserved record of carbonates beginning 3.5 billion years ago, the first 3 billion years of Earth history does not record evidence of methane oxidation. This is a curious absence. We think it might be linked to changes in ocean chemistry through time, but more work needs to be done to explore that.”

New evidence hints at global glaciation 716.5 million years ago

In this photo from Canada's Yukon Territory, an iron-rich layer of 716.5-million-year-old glacial deposits (maroon in color) is seen atop an older carbonate reef (gray in color) that formed in the tropics. -  Francis A. Macdonald/Harvard University
In this photo from Canada’s Yukon Territory, an iron-rich layer of 716.5-million-year-old glacial deposits (maroon in color) is seen atop an older carbonate reef (gray in color) that formed in the tropics. – Francis A. Macdonald/Harvard University

Geologists have found evidence that sea ice extended to the equator 716.5 million years ago, bringing new precision to a “snowball Earth” event long suspected to have taken place around that time.

Led by scientists at Harvard University, the team reports on its work this week in the journal Science. The new findings — based on an analysis of ancient tropical rocks that are now found in remote northwestern Canada — bolster the theory that our planet has, at times in the past, been ice-covered at all latitudes.

“This is the first time that the Sturtian glaciation has been shown to have occurred at tropical latitudes, providing direct evidence that this particular glaciation was a ‘snowball Earth’ event,” says lead author Francis A. Macdonald, an assistant professor in the Department of Earth and Planetary Sciences at Harvard. “Our data also suggests that the Sturtian glaciation lasted a minimum of 5 million years.”

The survival of eukaryotic life throughout this period indicates sunlight and surface water remained available somewhere on the surface of Earth. The earliest animals arose at roughly the same time, following a major proliferation of eukaryotes.

Even in a snowball Earth, Macdonald says, there would be temperature gradients on Earth and it is likely that ice would be dynamic: flowing, thinning, and forming local patches of open water, providing refuge for life.

“The fossil record suggests that all of the major eukaryotic groups, with the possible exception of animals, existed before the Sturtian glaciation,” Macdonald says. “The questions that arise from this are: If a snowball Earth existed, how did these eukaryotes survive? Moreover, did the Sturtian snowball Earth stimulate evolution and the origin of animals?”

“From an evolutionary perspective,” he adds, “it’s not always a bad thing for life on Earth to face severe stress.”

The rocks Macdonald and his colleagues analyzed in Canada’s Yukon Territory showed glacial deposits and other signs of glaciation, such as striated clasts, ice rafted debris, and deformation of soft sediments. The scientists were able to determine, based on the magnetism and composition of these rocks, that 716.5 million years ago they were located at sea level in the tropics, at about 10 degrees latitude.

“Because of the high albedo of ice, climate modeling has long predicted that if sea ice were ever to develop within 30 degrees latitude of the equator, the whole ocean would rapidly freeze over,” Macdonald says. “So our result implies quite strongly that ice would have been found at all latitudes during the Sturtian glaciation.”

Scientists don’t know exactly what caused this glaciation or what ended it, but Macdonald says its age of 716.5 million years closely matches the age of a large igneous province stretching more than 1,500 kilometers (932 miles) from Alaska to Ellesmere Island in far northeastern Canada. This coincidence could mean the glaciation was either precipitated or terminated by volcanic activity.

Geologists push back date basins formed, supporting frozen Earth theory

Even in geology, it’s not often a date gets revised by 500 million years.

But University of Florida geologists say they have found strong evidence that a half-dozen major basins in India were formed a billion or more years ago, making them at least 500 million years older than commonly thought. The findings appear to remove one of the major obstacles to the Snowball Earth theory that a frozen Earth was once entirely covered in snow and ice – and might even lend some weight to a controversial claim that complex life originated hundreds of million years earlier than most scientists currently believe.

“In modern geology, to revise the age of basins like this by 500 million years is pretty unique,” says Joe Meert, a UF associate professor of geology.

Agreed Abhijit Basu, a professor of geological studies at Indiana University: “The required revision is enormous – 500 million years or about 11 percent of total Earth history.”

Meert is one of eight authors of a paper on the research that recently appeared in the online edition of the journal Precambrian Research.

The Purana basins – which include the subject of the study, the Vindhyan basin – are located south of New Delhi in the northern and central regions of India. They are slight, mostly flat depressions in the Earth’s crust that span thousands of square miles. For decades, Meert said, most geologists have believed the basins formed 500 million to 700 million years ago when the Earth’s crust stretched, thinned and then subsided.

Meert said that date may have originated in early radiometric dating of sediment from the basin. Radiometric dating involves estimating age based on the decay or radioactive elements. Additionally, he said, apparent fossils retrieved from the basin seemed to have originated between 500 million and 700 million years ago.

The researchers were working on an unrelated project and had no intention of re-examining the basins’ age. But then a UF graduate student, Laura Gregory, dated a kimberlite retrieved from the Vindhyan basin to about 1,073 million years ago. A kimberlite is a volcanic rock that contains diamonds.

Gregory also used paleomagnetism, a technique that estimates where rocks were formed by using the orientation of their magnetic minerals. Curious about whether the kimberlite results would apply more generally to the region, fellow UF graduate student Shawn Malone compared the kimberlite’s orientation to other rocks from the Vindhyan basin. To his surprise, he found the orientations were virtually identical.

As a result, the geologists expanded the investigation, using a modified chain saw to drill wine-cork-sized cores out of dozens of rocks collected from 56 sites. Their contents all also had the same or very similar magnetic orientation, Meert said.

Much of the basins are composed of sediments that cannot be dated using any method. But Meert said the sediment also contains zircon, which can be dated using laser mass spectrometry – vaporizing tiny bits of the rocks with a laser, then analyzing their uranium and “daughter” lead contents to tease out their formation date based on rates of decay.

All the zircon the researchers tested originated 1,020 million years ago, Meert said.

The Snowball Earth theory posits that the Earth was covered in snow and ice from about 635 million to 700 million years ago. While much geological evidence has been found to support that theory worldwide, the Vindhyan and other Purana basins lacked numerous telltale signs, such as striated or scratched boulders formed when ice drags small pebbles over bedrock and boulder beds derived from glaciers known as tillites, Meert said. As a result, he said, the basins represented a prominent obstacle to the theory.

The new study removes that obstacle because it pushes back the origins of the basins to well before Snowball Earth would have occurred.

A 2007 study, conducted independently of the UF study and published in the Journal of Geology, dated rocks from another Purana basin to 1,020 million years ago, another 500-million-year revision. One of its authors was M.E. “Pat” Bickford, a professor emeritus at Syracuse University’s department of earth sciences. Bickford said the revisions of the age of the Purana basins calls into question the hypothesis that they formed when the supercontinent Rodinia broke up. Rodinia is thought to have separated into the modern continents about 700 million years ago, but the revisions make the basins too old for that split, Bickford said.

The UF research could also support a Swedish paleontologist’s controversial dating of multicellular creatures called Ediacarans from an older part of the basin to 1.6 billion years. But, said Meert, “Of all the implications of this research, the notion that Ediacaran-like organisms may be much older than 580 million years is probably the most speculative.”

The National Science Foundation funded the UF research.

Large methane release could cause abrupt climate change as happened 635 million years ago

Geologists Chris von der Borch (front) and David Mrofka (back) look for evidence of ancient methane seepage within tidal sediments seen in sea cliff exposures at Marino Rocks, South Australia. - Credit: M. Kennedy, UC Riverside.
Geologists Chris von der Borch (front) and David Mrofka (back) look for evidence of ancient methane seepage within tidal sediments seen in sea cliff exposures at Marino Rocks, South Australia. – Credit: M. Kennedy, UC Riverside.

UCR-led research team says methane-triggered global warming ended last ‘snowball’ ice age; dramatically reorganized Earth system

An abrupt release of methane, a powerful greenhouse gas, about 635 million years ago from ice sheets that then extended to Earth’s low latitudes caused a dramatic shift in climate, triggering a series of events that resulted in global warming and effectively ended the last “snowball” ice age, a UC Riverside-led study reports.

The researchers posit that the methane was released gradually at first and then in abundance from clathrates – methane ice that forms and stabilizes beneath ice sheets under specific temperatures and pressures. When the ice sheets became unstable, they collapsed, releasing pressure on the clathrates which began to degas.

“Our findings document an abrupt and catastrophic means of global warming that abruptly led from a very cold, seemingly stable climate state to a very warm also stable climate state with no pause in between,” said Martin Kennedy, a professor of geology in the Department of Earth Sciences, who led the research team.

“This tells us about the mechanism, which exists, but is dormant today, as well as the rate of change,” he added. “What we now need to know is the sensitivity of the trigger: how much forcing does it take to move from one stable state to the other, and are we approaching something like that today with current carbon dioxide warming.”

Study results appear in the May 29 issue of Nature.

Dolomite cement, formed from oxidized methane as it evolved from melting methane hydrates at the end of the snowball Earth glaciation, present in wave-cut platforms at Marino Rocks, South Australia. The dolomite is orange-red and formed vertical plumbing of tubes and vugs as methane passed upward and disrupted overlying sediment. - Credit: M. Kennedy, UC Riverside.
Dolomite cement, formed from oxidized methane as it evolved from melting methane hydrates at the end of the snowball Earth glaciation, present in wave-cut platforms at Marino Rocks, South Australia. The dolomite is orange-red and formed vertical plumbing of tubes and vugs as methane passed upward and disrupted overlying sediment. – Credit: M. Kennedy, UC Riverside.

According to the study, methane clathrate destabilization acted as a runaway feedback to increased warming, and was the tipping point that ended the last snowball Earth. (The snowball Earth hypothesis posits that the Earth was covered from pole to pole in a thick sheet of ice for millions of years at a time.)

“Once methane was released at low latitudes from destabilization in front of ice sheets, warming caused other clathrates to destabilize because clathrates are held in a temperature-pressure balance of a few degrees,” Kennedy said. “But not all the Earth’s methane has been released as yet. These same methane clathrates are present today in the Arctic permafrost as well as below sea level at the continental margins of the ocean, and remain dormant until triggered by warming.

“This is a major concern because it’s possible that only a little warming can unleash this trapped methane. Unzippering the methane reservoir could potentially warm the Earth tens of degrees, and the mechanism could be geologically very rapid. Such a violent, zipper-like opening of the clathrates could have triggered a catastrophic climate and biogeochemical reorganization of the ocean and atmosphere around 635 million years ago.”

Today, the Earth’s permafrost extends from the poles to approximately 60 degrees latitude. But during the last snowball Earth, which lasted from 790 to 635 million years ago, conditions were cold enough to allow clathrates to extend all the way to the equator.

According to Kennedy, the abruptness of the glacial termination, changes in ancient ocean-chemistry, and unusual chemical deposits in the oceans that occurred during the snowball Earth ice age have been a curiosity and a challenge to climate scientists for many decades.

“The geologic deposits of this period are quite different from what we find in subsequent deglaciation,” he said. “Moreover, they immediately precede the first appearance of animals on earth, suggesting some kind of environmental link. Our methane hypothesis is capable also of accounting for this odd geological, geochemical and paleooceanographic record.”

Also called marsh gas, methane is a colorless, odorless gas. As a greenhouse gas, it is about 30 times more potent than carbon dioxide, and has largely been held responsible for a warming event that occurred about 55 million years ago, when average global temperatures rose by 4-8 degrees Celsius.

When released into the ocean-atmosphere system, methane reacts with oxygen to form carbon dioxide and can cause marine dysoxia, which kills oxygen-using animals, and has been proposed as an explanation for major oceanic extinctions.

“One way to look at the present human influence on global warming is that we are conducting a global-scale experiment with Earth’s climate system,” Kennedy said. “We are witnessing an unprecedented rate of warming, with little or no knowledge of what instabilities lurk in the climate system and how they can influence life on Earth. But much the same experiment has already been conducted 635 million years ago, and the outcome is preserved in the geologic record. We see that strong forcing on the climate, not unlike the current carbon dioxide forcing, results in the activation of latent controls in the climate system that, once initiated, change the climate to a wholly different state.”

As part of their research, Kennedy and his colleagues collected hundreds of marine sediment samples in South Australia for stable isotope analysis, an important tool used in climate reconstruction. At UCR, the researchers analyzed the samples and found the broadest range of oxygen isotopic variation ever reported from marine sediments that they attribute to melting waters in ice sheets as well as destabilization of clathrates by glacial meltwater.

Next in their research, Kennedy and his colleagues will work on estimating how much of the temperature change that occurred 635 million years ago was due solely to methane.

Study heats up ‘snowball Earth’ debate

Research by University Professor Richard Peltier of physics reveals that the Earth’s surface 700 million years ago may have been warmer than previously thought.

Peltier developed a climate model that casts doubt on the popular “snowball Earth” hypothesis, a theory that posits the Earth was completely covered in ice and photosynthesis ceased during the late Neoproterozoic period.

The U of T physicist has found that the Neoproterozoic ocean’s natural carbon cycle produced a “negative feedback reaction” that actually prevented the equator region from completely freezing over, allowing photosynthesis to occur.

Peltier’s recent findings have found resonance among evolutionary biologists. The late Neoproterozoic period gave rise to arguably the most important period in Earth’s biological history – the Cambrian period. It was during this time when the major groups of animal life exploded onto the fossil record. Rock samples containing evidence of early organic life – ancestors to photosynthetic life – have been dated to before and after glacial periods. The idea that these ancestors to photosynthetic life could have existed during a period when there was no photosynthesis has been a topic of much debate.

“As the temperature of the Neoproterozoic ocean cools and moves towards a snowball state, more organic carbon is converted into carbon dioxide. The oxygen is drawn down out of the atmosphere into the ocean, re-mineralizing the organic matter and forcing respiration,” Peltier explained. “When respiration occurs, it generates carbon dioxide, part of which remains dissolved in the ocean, but part of which is forced out of the ocean into the atmosphere which enhances the greenhouse effect and prevents the cooling.

“The mathematical model supports oscillatory glaciations and de-glaciations on a timescale that’s similar to the timescale that people have argued were appropriate for the Neoproterozoic,” he added.

Doctoral student Yonggang Liu and John Crowley, a former summer research student in Peltier’s lab, now pursuing doctoral studies at Harvard, co-authored the paper, published in Nature late last year.

The study builds on the findings published by Professor Dan Rothman from the Massachusetts Institute of Technology that suggest that the Neoproterozoic ocean was very rich in carbon life and findings published by Peltier on the cover of Nature in 2000 that, for the first time, demonstrated that while huge deep glaciations did exist, a large amount of water near the equator was left unfrozen. At the time, adherents to the “snowball Earth” theory coined the term “slushball Earth” to describe Peltier’s findings.

Low Oxygen and Molybdenum Levels in Ancient Oceans Delayed Evolution of Life by Two Billion Years


UCR-led study tracked biogeochemical signatures preserved in ancient sedimentary rocks to establish nature and timing of oxygenation of Earth’s atmosphere

A deficiency of oxygen and the heavy metal molybdenum in the ancient deep ocean may have delayed the evolution of animal life on Earth by nearly two billion years, a study led by UC Riverside biogeochemists has found.

The researchers arrived at their result by tracking molybdenum in black shales, which are a kind of sedimentary rock rich in organic matter and usually found in the deep ocean. Molybdenum is a key micronutrient for life and serves as a proxy for oceanic and atmospheric oxygen amounts.

Study results appear in the March 27 issue of Nature.

Following the initial rise of oxygen in the Earth’s atmosphere 2.4 billion years ago, oxygen was transferred to the surface ocean to support oxygen-demanding microorganims. Yet the diversity of these single-celled life forms remained low, and their multicellular descendants, the animals, did not appear until about 600 million years ago, explained Timothy Lyons, a professor of biogeochemistry in the Department of Earth Sciences and one of the study’s authors.

Suspecting that deficiencies in oxygen and molybdenum might explain this evolutionary lag, Lyons and his colleagues measured abundances of molybdenum in ancient marine sediments over time to estimate how much of the metal had been dissolved in the seawater in which the sediments formed.

The researchers found significant, firsthand evidence for a molybdenum-depleted ocean relative to the high levels measured in modern, oxygen-rich seawater.

“These molybdenum depletions may have retarded the development of complex life such as animals for almost two billion years of Earth history,” Lyons said. “The amount of molybdenum in the ocean probably played a major role in the development of early life. As in the case of iron today, molybdenum can be thought of as a life-affirming micronutrient that regulates the biological cycling of nitrogen in the ocean.

“At the same time, molybdenum’s low abundance in the early ocean tracks the global extent of oxygen-poor seawater and implies that the amount of oxygen in the atmosphere was still low.

“Knowing the amount of oxygen in the early ocean is important for many reasons, including a refined understanding of how and when appreciable oxygen first began to accumulate in the atmosphere,” Lyons said. “These steps in oxygenation are what gave rise ultimately to the first animals almost 600 million years ago – just the last tenth or so of Earth history.”

Earth’s oxygenation

For animal life to commence, survive and eventually expand on Earth, a threshold amount of oxygen – estimated to be on the order of 1 to 10 percent of present atmospheric levels of oxygen – was needed.

Past research has shown that Earth’s oxygenation occurred in two major steps:

The first step, around 2.4 billion years ago, took place as the ocean transitioned to a state where only the surface ocean was oxygenated by photosynthesizing bacteria, while the deep ocean was relatively oxygen-free.

The second step, around 600 million years ago, marked the occasion when the entire ocean became fully oxygenated through a process not yet fully understood.

“We wanted to know what the state of the ocean was between the two steps,” said Clinton Scott, a graduate student working in Lyons’s lab and the first author of the research paper. “By tracking molybdenum in shales rich in organic matter, we found the deep ocean remained oxygen- and molybdenum-deficient after the first step. This condition may have had a negative impact on the evolution of early eukaryotes, our single-celled ancestors. The molybdenum record also tells us that the deep ocean was already fully oxygenated by around 550 million years ago.”

According to Scott, the timing of the oxygenation steps suggests that significant events in Earth history are related. Scientists have long speculated that the evolution of the first animals was linked somehow to the so-called Snowball Earth hypothesis, which posits that the Earth was covered from pole to pole in a thick sheet of ice for millions of years at a time. “The second oxygenation step took place not long after the last Snowball Earth episode ended around 600 million years ago,” Scott said. “So one question is: Did this global glaciation play a role in the increasing abundance of oxygen which, in turn, enabled the evolution of animals?”

Scott and Lyons were joined in the research by A. Bekker of the Carnegie Institution of Washington, DC; Y. Shen of the Université du Québec à Montréal, Canada; S.W. Poulton of Newcastle University, Newcastle upon Tyne, United Kingdom; X. Chu of the Chinese Academy of Sciences, Beijing, China; and A.D. Anbar of Arizona State University, Tempe, Ariz.

The research was supported by grants from the U.S. National Science Foundation Division of Earth Sciences and the NASA Astrobiology Institute.

More about molybdenum as a proxy for ocean chemistry

Molybdenum, a metal abundant in the ocean today but less so at times in the past, is an excellent tracer of ancient chemistry for two reasons. First, the primary source of molybdenum to the ocean is oxidative weathering of continental crust, requiring oxygen in the atmosphere. Second, molybdenum is removed primarily in marine sediments where oxygen is absent and sulfide is abundant. Thus the enrichment of molybdenum in ancient organic-rich shales requires oxygen in the atmosphere but high sulfur and very low or no oxygen in the deep ocean. This combination is relatively rare today but may have been common when oxygen was less abundant in the earlier atmosphere.

When oxygen is available in the atmosphere, the amount of dissolved molybdenum in seawater is determined by the extent of hydrogen-sulfide-containing sediments and bottom waters (the colder, more isolated, lowermost layer of ocean water). Where sulfidic environments are widespread, the pool of molybdenum remaining in seawater is small, growing as the sulfidic environments shrink. The amount of molybdenum in the seawater is reflected in the magnitude of molybdenum enrichment in shales deposited in the deep ocean.

The UCR-led team of researchers estimated the size of the oceanic reservoir, and thus the extent of sulfidic bottom waters and sediments, based on the concentration of molybdenum in ancient black shales. They did so by dissolving the samples in a cocktail of acids and analyzing the dissolved rock for concentration using a mass spectrometer. The amount of this metal in the shales tracks the oxygen state of the early ocean and atmosphere and also points to the varying abundance of this essential ingredient of life. Molybdenum limitations may have delayed the development of eukaryotes, including the first animals, our earliest multicellular cousins.