From astrobio.net: “Rare Mineral found in a Wisconsin Crater”

Astrobiology Magazine

Jan 14, 2015
Aaron L. Gronstal

With support from the NASA Astrobiology Program, Cavosie brought students from the University of Puerto Rico to study outcrops at the Rock Elm meteorite impact structure. Reidite was found in the samples they collected. Credit: Aaron Cavosie

Scientists have discovered one of the rarest minerals on Earth in a Wisconsin impact crater.

Aaron Cavosie of the University of Puerto Rico, and member of the NASA Astrobiology Institute Team at the University of Wisconsin, brought students to an impact site in Rock Elm, Wisconsin to collect samples. In those samples, Cavosie and colleagues discovered the mineral reidite, making Rock Elm the fourth site on Earth where the mineral has been found in nature.

Reidite is created at high pressures and was first identified in the laboratory in the 1960s. The conditions in which reidite forms have been well-constrained by experiments in the lab but, prior to Rock Elm, it was only found naturally in the Chesapeake Bay Impact Structure (Virginia), the Ries Crater (Germany), and the Xiuyan Crater (China).

The Rock Elm structure is 6.5 kilometers in diameter and was formed during the Middle Ordovician. This means that the reidite found at Rock Elm is at least 450 million years old, making it the oldest preserved reidite yet discovered.

Another important aspect of the research is that the reidite was found in sandstone – the first time the mineral was spotted in this type of rock. There are many other impact structures that have been formed in sandstone, and its possible that a re-examination of these sites could reveal more reidite.

“I get the sense that, because reidite had never been found in this kind of rock, if something’s never found there, your not going to go look for it purposefully,” said Cavosie in an interview with Wisconsin Public Radio. “Now that we’ve identified this recorder of even far more extreme impact conditions than what was known previously at Rock Elm, that tool can be applied to many, many other localities to try to recreate the impact conditions and better understand the effects on the surface environments of some of these impacts.”

Wisconsin Public Radio produced an interview with Aaron Cavosie and Bill Cordua of UW-River Falls, who discovered the Rock Elm disturbance. To listen to the show, visit: http://www.wpr.org/listen/682916

The initial findings were presented at the 2014 GSA Annual Meeting in Vancouver.

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From U Chicago: “Modern genetics confirm ancient relationship between fins and hands”

University of Chicago

December 29, 2014
John Easton

Paleontologists have documented the evolutionary adaptations necessary for ancient lobe-finned fish to transform pectoral fins used underwater into strong, bony structures, such as those of Tiktaalik roseae. This enabled these emerging tetrapods, animals with limbs, to crawl in shallow water or on land. But evolutionary biologists have wondered why the modern structure called the autopod—comprising wrists and fingers or ankles and toes—has no obvious morphological counterpart in the fins of living fishes.

Tiktaalik

In the Dec. 22, 2014, issue of the Proceedings of the National Academy of Sciences, researchers argue previous efforts to connect fin and fingers fell short because they focused on the wrong fish. Instead, they found the rudimentary genetic machinery for mammalian autopod assembly in a non-model fish, the spotted gar, whose genome was recently sequenced.

“Fossils show that the wrist and digits clearly have an aquatic origin,” said Neil Shubin, the Robert R. Bensley Distinguished Service Professor of Organismal Biology and Anatomy and a leader of the team that discovered Tiktaalik in 2004. “But fins and limbs have different purposes. They have evolved in different directions since they diverged. We wanted to explore, and better understand, their connections by adding genetic and molecular data to what we already know from the fossil record.”

Initial attempts to confirm the link based on shape comparisons of fin and limb bones were unsuccessful. The autopod differs from most fins. The wrist is composed of a series of small nodular bones, followed by longer thin bones that make up the digits. The bones of living fish fins look much different, with a set of longer bones ending in small circular bones called radials.

The primary genes that shape the bones, known as the HoxD and HoxA clusters, also differ. The researchers first tested the ability of genetic “switches” that control HoxD and HoxA genes from teleosts—bony, ray-finned fish—to shape the limbs of developing transgenic mice. The fish control switches, however, did not trigger any activity in the autopod.

Teleost fish—a vast group that includes almost all of the world’s important sport and commercial fish—are widely studied. But researchers began to realize they were not the ideal comparison for studies of how ancient genes were regulated. When they searched for wrist and digit-building genetic switches, they found “a lack of sequence conservation” in teleost species.

They traced the problem to a radical change in the genetics of teleost fish. More than 300 million years ago, after the fish-like creatures that would become tetrapods split off from other bony fish, a common ancestor of the teleost lineage went through a whole-genome duplication—a phenomenon that has occurred multiple times in evolution.

By doubling the entire genetic repertoire of teleost fish, this WGD provided them with enormous diversification potential. This may have helped teleosts to adapt, over time, to a variety of environments worldwide. In the process, “the genetic switches that control autopod-building genes were able to drift and shuffle, allowing them to change some of their function, as well as making them harder to identify in comparisons to other animals, such as mice,” said Andrew Gehrke, a graduate student in the Shubin Lab and lead author of the study.

Not all bony fishes went through the whole genome duplication, however. The spotted gar, a primitive freshwater fish native to North America, split off from teleost fishes before the WGD.

When the research team compared Hox gene switches from the spotted gar with tetrapods, they found “an unprecedented and previously undescribed level of deep conservation of the vertebrate autopod regulatory apparatus.” This suggests, they note, a high degree of similarity between “distal radials of bony fish and the autopod of tetrapods.”

They tested this by inserting gar gene switches related to fin development into developing mice. This evoked patterns of activity that were “nearly indistinguishable,” the authors note, from those driven by the mouse genome.

“Overall,” the researchers conclude, “our results provide regulatory support for an ancient origin of the ‘late’ phase of Hox expression that is responsible for building the autopod.”

This study was supported by the Brinson Foundation, the National Science Foundation, the Brazilian National Council for Scientific and Technological Development grants, the National Institutes of Health, the Volkswagen Foundation in Germany, the Alexander von Humboldt-Foundation, the Spanish and Andalusian governments, and Proyecto de Excelencia.

Additional authors include Mayuri Chandran and Tetsuya Nakamura from the University of Chicago; Igor Schneider from the Instituto de Ciencias Biologicas, Universida de Federal do Para, Belem, Brazil; Elisa de la Calle-Mustienes, Juan J. Tena, Carlos Gomez-Marin and José Luis Gómez-Skarmeta from the Centro Andaluz de Biología del Desarrollo, Sevilla, Spain; and Ingo Braasch and John H. Postlethwait from the Institute of Neuroscience, University of Oregon.

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One of the world’s premier academic and research institutions, the University of Chicago has driven new ways of thinking since our 1890 founding. Today, UChicago is an intellectual destination that draws inspired scholars to our Hyde Park and international campuses, keeping UChicago at the nexus of ideas that challenge and change the world.

From Leeds: “Scientists observe the Earth grow a new layer under an Icelandic volcano”

University of Leeds

15 December 2014
No Writer Credit

New research into an Icelandic eruption has shed light on how the Earth’s crust forms, according to a paper published today in Nature.

When the Bárðarbunga volcano, which is buried beneath Iceland’s Vatnajökull ice cap, reawakened in August 2014, scientists had a rare opportunity to monitor how the magma flowed through cracks in the rock away from the volcano.

The molten rock forms vertical sheet-like features known as dykes, which force the surrounding rock apart.

Study co-author Professor Andy Hooper from the Centre for Observation and Modelling of Earthquakes, volcanoes and Tectonics (COMET) at the University of Leeds explained: “New crust forms where two tectonic plates are moving away from each other. Mostly this happens beneath the oceans, where it is difficult to observe.

“However, in Iceland this happens beneath dry land. The events leading to the eruption in August 2014 are the first time that such a rifting episode has occurred there and been observed with modern tools, like GPS and satellite radar.”

Although it has a long history of eruptions, Bárðarbunga has been increasingly restless since 2005. There was a particularly dynamic period in August and September this year, when more than 22,000 earthquakes were recorded in or around the volcano in just four weeks, due to stress being released as magma forced its way through the rock.

Using GPS and satellite measurements, the team were able to track the path of the magma for over 45km before it reached a point where it began to erupt, and continues to do so to this day. The rate of dyke propagation was variable and slowed as the magma reached natural barriers, which were overcome by the build-up of pressure, creating a new segment.

The dyke grows in segments, breaking through from one to the next by the build up of pressure. This explains how focused upwelling of magma under central volcanoes is effectively redistributed over large distances to create new upper crust at divergent plate boundaries, the authors conclude.

As well as the dyke, the team found ‘ice cauldrons’ – shallow depressions in the ice with circular crevasses, where the base of the glacier had been melted by magma. In addition, radar measurements showed that the ice inside Bárðarbunga’s crater had sunk by 16m, as the volcano floor collapsed.

COMET PhD student Karsten Spaans from the University of Leeds, a co-author of the study, added: “Using radar measurements from space, we can form an image of caldera movement occurring in one day. Usually we expect to see just noise in the image, but we were amazed to see up to 55cm of subsidence.”

Like other liquids, magma flows along the path of least resistance, which explains why the dyke at Bárðarbunga changed direction as it progressed. Magma flow was influenced mostly by the lie of the land to start with, but as it moved away from the steeper slopes, the influence of plate movements became more important.

Summarising the findings, Professor Hooper said: “Our observations of this event showed that the magma injected into the crust took an incredibly roundabout path and proceeded in fits and starts.

“Initially we were surprised at this complexity, but it turns out we can explain all the twists and turns with a relatively simple model, which considers just the pressure of rock and ice above, and the pull exerted by the plates moving apart.

The paper Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland is published in Nature on 15 December 2014.

The research leading to these results has received funding from the European Community’s Seventh Framework Programme under Grant Agreement No. 308377 (Project FUTUREVOLC).

Read the paper here: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14111.html

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The University of Leeds was founded in 1904, but its origins go back to t­he nineteenth century with the founding of the Leeds School of Medicine in 1831 and then the Yorkshire College of Science in 1874.

From Princeton: “New, tighter timeline confirms ancient volcanism aligned with dinosaurs’ extinction”

Princeton University

December 18, 2014
Morgan Kelly, Office of Communications

A definitive geological timeline shows that a series of massive volcanic explosions 66 million years ago spewed enormous amounts of climate-altering gases into the atmosphere immediately before and during the extinction event that claimed Earth’s non-avian dinosaurs, according to new research from Princeton University.

A primeval volcanic range in western India known as the Deccan Traps, which were once three times larger than France, began its main phase of eruptions roughly 250,000 years before the Cretaceous-Paleogene, or K-Pg, extinction event, the researchers report in the journal Science. For the next 750,000 years, the volcanoes unleashed more than 1.1 million cubic kilometers (264,000 cubic miles) of lava. The main phase of eruptions comprised about 80-90 percent of the total volume of the Deccan Traps’ lava flow and followed a substantially weaker first phase that began about 1 million years earlier.

A definitive geological timeline from Princeton University researchers shows that a series of massive eruptions 66 million years ago in a primeval volcanic range in western India known as the Deccan Traps played a role in the extinction event that claimed Earth’s non-avian dinosaurs, and challenges the dominant theory that a meteorite impact was the sole cause of the extinction. Pictured above are the Deccan Traps near Mahabaleshwar, India. (Image courtesy of Gerta Keller, Department of Geosciences)

The results support the idea that the Deccan Traps played a role in the K-Pg extinction, and challenge the dominant theory that a meteorite impact near present-day Chicxulub, Mexico, was the sole cause of the extinction. The researchers suggest that the Deccan Traps eruptions and the Chicxulub impact need to be considered together when studying and modeling the K-Pg extinction event.

The Deccan Traps’ part in the K-Pg extinction is consistent with the rest of Earth history, explained lead author Blair Schoene, a Princeton assistant professor of geosciences who specializes in geochronology. Four of the five largest extinction events in the last 500 million years coincided with large volcanic eruptions similar to the Deccan Traps. The K-Pg extinction is the only one that coincides with an asteroid impact, he said.

“The precedent is there in Earth history that significant climate change and biotic turnover can result from massive volcanic eruptions, and therefore the effect of the Deccan Traps on late-Cretaceous ecosystems should be considered,” Schoene said.

DeccanTrap_map
The researchers suggest that the Deccan Traps eruptions and the meteorite impact near present-day Chicxulub, Mexico, need to be considered together when studying and modeling the Cretaceous-Paleogene extinction event. The main eruption phases for the Deccan Traps (in brown), which were once three times larger than France, began roughly 250,000 years before the extinction event, the researchers found. For the next 750,000 years, the volcanoes unleashed more than 1.1 million cubic kilometers (264,000 cubic miles) of lava, which comprised about 80-90 percent of the total volume of the Deccan Traps’ lava flow. The amount of carbon dioxide and sulfur dioxide the volcanoes poured out would have caused severe ecological fallout. (Illustration by Matilda Luk, Office of Communications)

The researchers used a precise rock-dating technique to narrow significantly the timeline for the start of the main eruption, which until now was only known to have occurred within 1 million years of the K-Pg extinction, Schoene said. The Princeton group will return to India in January to collect more samples with the purpose of further constraining eruption rates during the 750,000-year volcanic episode.

Schoene and his co-authors gauged the age of petrified lava flows known as basalt by comparing the existing ratio of uranium to lead given the known rate at which uranium decays over time. The uranium and lead were found in tiny grains — less than a half-millimeter in size — of the mineral zircon. Zircon is widely considered Earth’s best “time capsule” because it contains a lot of uranium and no lead when it crystallizes, but it is scarce in basalts that cooled quickly. The researchers took the unusual approach of looking for zircon in volcanic ash that had been trapped between lava flows, as well as within thick basalt flows where lava would have cooled more slowly.

The zircon dated from these layers showed that 80-90 percent of the Deccan Traps eruptions occurred in less than a million years, and began very shortly — in geological terms — before the K-Pg extinction. To produce useful models for events such as the K-Pg extinction, scientists want to know the sequence of events to within tens of thousands of years or better, not millions, Schoene said. Margins of millions of years are akin to “a history book with events that have no dates and are not written in chronological order,” he said.

“We need to know which events happened first and how long before other events, such as when did the Deccan eruptions happen in relation to the K-Pg extinction,” Schoene said. “We’re now able to place a higher resolution timeframe on these eruptions and are one step closer to finding out what the individual effects of the Deccan Traps eruptions were relative to the Chicxulub meteorite.”

Vincent Courtillot, a geophysicist and professor at Paris University Diderot, said that the paper is important and “provides a significant improvement on the absolute dating of the Deccan Traps.” Courtillot, who is familiar with the Princeton work but had no role in it, led a team that reported in the Journal of Geophysical Research in 2009 that Deccan volcanism occurred in three phases, the second and largest of which coincides with the K-Pg mass extinction. Numerous other papers from his research groups are considered essential to the development of the Deccan Traps hypothesis. (The Princeton researchers also plan to test the three-phases hypothesis, Schoene said. Their data already suggests that the second and third phase might be a single period of eruptions bridged by smaller, “pulse” eruptions, he said.)

DeccanTrap_rocks
The researchers took an unusual approach to find the mineral needed to construct the timeline for the start of the main Deccan Traps eruption. They compared the existing ratio of uranium to lead in petrified lava flows known as basalts given the known rate at which uranium decays over time. To have enough uranium, however, the researchers needed the mineral zircon, which is scarce in basalts that cooled quickly. Turning to new sources, the researchers found zircon in soil deposits known as red boles (right) that formed in between eruptions and contain volcanic ash (left) that had been trapped between lava flows. They also located zircon within thick basalt flows where lava would have cooled more slowly. (Images courtesy of Blair Schoene, Department of Geosciences)

The latest work builds on the long-time work by co-author Gerta Keller, a Princeton professor of geosciences, to establish the Deccan Traps as a main cause of the K-Pg extinction. Virginia Tech geologist Dewey McLean first championed the theory 30 years ago and Keller has since become a prominent voice among a large group of scientists who advocate the idea. In 2011, Keller published two papers that together proposed a one-two punch of Deccan volcanism and meteorite strikes that ended life for more than half of Earth’s plants and animals.

Existing models of the environmental effects of the Deccan eruptions used timelines two to three times longer than what the researchers found, which underestimated the eruptions’ ecological fallout, Keller explained. The amount of carbon dioxide and sulfur dioxide the volcanoes poured out would have produced, respectively, a long-term warming and short-term cooling of the oceans and land, and resulted in highly acidic bodies of water, she said.

Because these gases dissipate somewhat quickly, however, a timeline of millions of years understates the volcanoes’ environmental repercussions, while a timeframe of hundreds of thousands of years — particularly if the eruptions never truly stopped — provides a stronger correlation. The new work confirms past work by placing the largest Deccan eruptions nearer the K-Pg extinction, but shows a much shorter time frame of just 250,000 years, Keller said.

“These results have significantly strengthened the case for volcanism as the primary cause for the mass extinction, as well as for the observed rapid climate changes and ocean acidification,” Keller said.

“The Deccan Traps mass extinction hypothesis has already enjoyed wide acceptance based on our earlier work and a number of studies have independently confirmed the global effects of Deccan volcanism just prior to the mass extinction,” she said. “The current results will go a long way to strengthen the earlier results as well as further challenge the dominance of the Chicxulub hypothesis.”

Schoene and Keller worked with Kyle Samperton, a doctoral student in Schoene’s research group; Thierry Adatte, a geologist with the University of Lausanne in Switzerland and Keller’s longtime collaborator; Brian Gertsch, who earned his Ph.D. from Princeton in 2010 and is now a research assistant at the University of Lausanne; Syed Khadri, a geology professor at Amravati University in India; and graduate student Michael Eddy and geology professor Samuel Bowring at the Massachusetts Institute of Technology.

The paper, U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction, was published Dec. 11 in Science. This work was supported by the Princeton Department of Geosciences’ Scott Fund; the National Science Foundation’s Continental Dynamics and Sedimentary Geology and Paleobiology programs; and the NSF Office of International Science and Engineering’s India Program (grant nos. EAR-0447171 and EAR-1026271).

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About Princeton: Overview

Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

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From AAAS: “Greenhouse emissions similar to today’s may have triggered massive temperature rise in Earth’s past”

AAAS

15 December 2014
Tim Wogan

About 55.5 million years ago, a burst of carbon dioxide raised Earth’s temperature 5°C to 8°C, which had major impacts on numerous species of plants and wildlife. Scientists analyzing ancient soil samples now say a previous burst of the greenhouse gas preceded this event, known as the Paleocene-Eocene thermal maximum (PETM), and probably triggered it. Moreover, they believe humans are pumping similar levels of carbon dioxide into the atmosphere right now, raising concerns that our own emissions may also destabilize Earth’s climate, triggering the planet to emit devastating bursts of carbon in the future.

This figure is a simplified, schematic representation of the flows of energy between space, the atmosphere, and the Earth’s surface, and shows how these flows combine to trap heat near the surface and create the greenhouse effect. Energy exchanges are expressed in watts per square meter (W/m2) and derived from Kiehl & Trenberth (1997). The figure does not appear clear. I would change the 195 to atmospheric radiation into space, as it does not include the 40 radiated from the surface. Complete figure: (http://www.cgd.ucar.edu/cas/abstracts/files/kevin1997_1.html)

The sun is responsible for virtually all energy that reaches the Earth’s surface. Direct overhead sunlight at the top of the atmosphere provides 1366 W/m2; however, geometric effects and reflective surfaces limit the light which is absorbed at the typical location to an annual average of ~235 W/m2. If this were the total heat received at the surface, then, neglecting changes in albedo, the Earth’s surface would be expected to have an average temperature of -18 °C (Lashof 1989). Of the surface heat captured by the atmosphere, more than 75% can be attributed to the action of greenhouse gases that absorb thermal radiation emitted by the Earth’s surface. The atmosphere in turn transfers the energy it receives both into space (38%) and back to the Earth’s surface (62%), where the amount transferred in each direction depends on the thermal and density structure of the atmosphere. This process by which energy is recycled in the atmosphere to warm the Earth’s surface is known as the greenhouse effect and is an essential piece of Earth’s climate. Under stable conditions, the total amount of energy entering the system from solar radiation will exactly balance the amount being radiated into space, thus allowing the Earth to maintain a constant average temperature over time.
However, recent measurements indicate that the Earth is presently absorbing 0.85 ± 0.15 W/m2 more than it emits into space (Hansen et al. 2005). An overwhelming majority of climate scientists believe that this asymmetry in the flow of energy has been significantly increased by human emissions of greenhouse gases [1]. This figure was created by Robert A. Rohde from published data and is part of the Global Warming Art project

Rocks from the Bighorn Basin in Wyoming were used to reconstruct Earth’s climate at the time of the Paleocene-Eocene thermal maximum. (Scott Wing, Smithsonian Institution)

The paper implies that even if we stopped emitting carbon dioxide right now, our descendants might still face huge temperature rises, says paleoclimatologist Gabriel Bowen of the University of Utah in Salt Lake City, the lead author of the new research. “It is a possibility,” he says, “and it’s a scary one.”

Scientists accept that a massive injection of carbon into the atmosphere caused the PETM, but they don’t agree about where the gas came from. Some researchers say it originated from the release of carbon locked up under the ocean by an undersea landslide; others blame a comet crashing into Earth, causing carbon from both the comet and Earth to be oxidized to carbon dioxide and potentially causing wildfires or burning of carbon-rich peat bogs on Earth. They also don’t know how long the release lasted, with recent estimates ranging from 10 years to 20,000 years.

One of the best ways to measure the prehistoric release of carbon into the atmosphere is to look at the ratio of two types of carbon atoms called isotopes. Carbon has two stable isotopes: About 99% of natural carbon is carbon-12, whereas the remaining 1% is mainly the heavier carbon-13, with trace amounts of radioactive carbon-14 that decay within a few thousand years to nitrogen. Living organisms have a slight preference for the lighter isotope, so carbon derived from organic sources (such as fossil fuels) is slightly depleted in carbon-13. If that carbon gets returned to the atmosphere at a faster rate than normal, atmospheric carbon dioxide has less carbon-13 than normal. Plants taking up this carbon dioxide become even more carbon-13 depleted, and when they decompose, this depletion is recorded in the soil.

Sedimentary rock samples that have been compacted from soils formed at the time of the PETM contain less carbon-13 than normal. Sedimentary rocks of the Bighorn Basin in Wyoming contain one of the best records of soils from this period. Geologists have studied them for more than 100 years, but to obtain samples from soils of different periods, geologists had to analyze surface rocks from different parts of the basin and try to piece together a continuous geological history. Therefore, the Bighorn Basin Coring Project, run by the University of New Hampshire, Durham, drilled approximately 1 km of core from each of three different points in the basin to give geologists three clear, continuous records of how the soils had varied over time in a particular place.

Bowen and colleagues analyzed one of these cores, tracking the variations in carbon isotope ratios in greater detail than had been previously possible by examining surface rocks. They report online today in Nature Geoscience that in soils beneath those laid down during the main rise in temperature about 55.5 million years ago, there was a distinct drop in the proportion of carbon-13. In soils immediately on top of these, the ratio seemed to recover to its normal value. Finally, soils on top of these showed a large drop in the proportion of carbon-13 corresponding to the PETM itself.

So what was going on? The researchers concluded that there must have been two separate releases of carbon. The first, smaller release, about 2000 years before the main temperature rise, was followed by a recovery to normal climatic conditions. Later, a second, larger pulse caused the main event. “I’m fairly convinced that they’re related,” Bowen says. “We see nothing remotely similar during the many hundreds of thousands of years before this event. To have within a few thousand years these two major carbon isotope shifts and have that be circumstantial would be quite remarkable.”

The researchers used climate models to investigate how the initial, smaller heating could have triggered the later surge in temperature. They estimate that the first thermal pulse is likely to have warmed Earth’s atmosphere by 2°C to 3°C, but that the atmospheric temperature would have gradually returned to normal as the heat was absorbed into the deep ocean. However, when that heat finally reached the ocean floor, it might have melted methane ices called clathrates, releasing the methane into the ocean and allowing it to make its way into the atmosphere. As a greenhouse gas, methane is 21 times more potent than carbon dioxide, so a sudden spike in methane emissions could lead to huge climate change.

“The connection between these two pulses is something that it’s going to be really important to get a handle on,” Bowen says. The researchers believe the rate at which carbon dioxide escaped into the atmosphere during both bursts is unlikely to have been greater than the rate at which humans are emitting it now, and it may have been considerably lower. “Carbon release back then looked a lot like human fossil fuel emissions today,” Bowen says. “So we might learn a lot about the future from changes in climate, plants, and animal communities 55.5 million years ago.”

“We think this is really good news for our contention that the release of carbon was very fast,” says marine geologist James Wright of Rutgers University, New Brunswick, an advocate of the comet impact hypothesis.

Wright is not convinced, however, about the importance of the first pulse in triggering the second. He suggests that the most logical interpretation of the apparent cooling after the first pulse is that its significance was less than Bowen’s group believes, with limited effect on the overall ocean temperature, and that not just the atmosphere but rather the entire planet quickly returned to normal. “If that’s the case, then the first has nothing to do with the second,” Wright says. That, in turn, would require an alternative explanation for the PETM such as a comet impact.

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From astrobio.net: “Warmer Pacific Ocean could release millions of tons of seafloor methane”

University of Washington

December 9, 2014
Hannah Hickey

Off the West Coast of the United States, methane gas is trapped in frozen layers below the seafloor. New research from the University of Washington shows that water at intermediate depths is warming enough to cause these carbon deposits to melt, releasing methane into the sediments and surrounding water.

Researchers found that water off the coast of Washington is gradually warming at a depth of 500 meters, about a third of a mile down. That is the same depth where methane transforms from a solid to a gas. The research suggests that ocean warming could be triggering the release of a powerful greenhouse gas.

Sonar image of bubbles rising from the seafloor off the Washington coast. The base of the column is 1/3 of a mile (515 meters) deep and the top of the plume is at 1/10 of a mile (180 meters) deep.Brendan Philip / UW

“We calculate that methane equivalent in volume to the Deepwater Horizon oil spill is released every year off the Washington coast,” said Evan Solomon, a UW assistant professor of oceanography. He is co-author of a paper to appear in Geophysical Research Letters.

While scientists believe that global warming will release methane from gas hydrates worldwide, most of the current focus has been on deposits in the Arctic. This paper estimates that from 1970 to 2013, some 4 million metric tons of methane has been released from hydrate decomposition off Washington. That’s an amount each year equal to the methane from natural gas released in the 2010 Deepwater Horizon blowout off the coast of Louisiana, and 500 times the rate at which methane is naturally released from the seafloor.

Dissociation of Cascadia margin gas hydrates in response to contemporary ocean warming
Geophysical Research Letters | Dec. 5, 2014

“Methane hydrates are a very large and fragile reservoir of carbon that can be released if temperatures change,” Solomon said. “I was skeptical at first, but when we looked at the amounts, it’s significant.”

Methane is the main component of natural gas. At cold temperatures and high ocean pressure, it combines with water into a crystal called methane hydrate. The Pacific Northwest has unusually large deposits of methane hydrates because of its biologically productive waters and strong geologic activity. But coastlines around the world hold deposits that could be similarly vulnerable to warming.

“This is one of the first studies to look at the lower-latitude margin,” Solomon said. “We’re showing that intermediate-depth warming could be enhancing methane release.”
map of Washington coast

The yellow dots show all the ocean temperature measurements off the Washington coast from 1970 to 2013. The green triangles are places where scientists and fishermen have seen columns of bubbles. The stars are where the UW researchers took more measurements to check whether the plumes are due to warming water.Una Miller / UW

Co-author Una Miller, a UW oceanography undergraduate, first collected thousands of historic temperature measurements in a region off the Washington coast as part of a separate research project in the lab of co-author Paul Johnson, a UW professor of oceanography. The data revealed the unexpected sub-surface ocean warming signal.

“Even though the data was raw and pretty messy, we could see a trend,” Miller said. “It just popped out.”

The four decades of data show deeper water has, perhaps surprisingly, been warming the most due to climate change.

“A lot of the earlier studies focused on the surface because most of the data is there,” said co-author Susan Hautala, a UW associate professor of oceanography. “This depth turns out to be a sweet spot for detecting this trend.” The reason, she added, is that it lies below water nearer the surface that is influenced by long-term atmospheric cycles.

The warming water probably comes from the Sea of Okhotsk, between Russia and Japan, where surface water becomes very dense and then spreads east across the Pacific. The Sea of Okhotsk is known to have warmed over the past 50 years, and other studies have shown that the water takes a decade or two to cross the Pacific and reach the Washington coast.

Map of the Sea of Okhotsk

“We began the collaboration when we realized this is also the most sensitive depth for methane hydrate deposits,” Hautala said. She believes the same ocean currents could be warming intermediate-depth waters from Northern California to Alaska, where frozen methane deposits are also known to exist.

The yellow dots show all the ocean temperature measurements off the Washington coast from 1970 to 2013. The green triangles are places where scientists and fishermen have seen columns of bubbles. The stars are where the UW researchers took more measurements to check whether the plumes are due to warming water.Una Miller / UW

Researchers used a coring machine to gather samples of sediment off Washington’s coast to see if observations match their calculations for warming-induced methane release. The photo was taken in October aboard the UW’s Thomas G. Thompson research vessel.Robert Cannata / UW

Warming water causes the frozen edge of methane hydrate to move into deeper water. On land, as the air temperature warms on a frozen hillside, the snowline moves uphill. In a warming ocean, the boundary between frozen and gaseous methane would move deeper and farther offshore. Calculations in the paper show that since 1970 the Washington boundary has moved about 1 kilometer – a little more than a half-mile – farther offshore. By 2100, the boundary for solid methane would move another 1 to 3 kilometers out to sea.

Estimates for the future amount of gas released from hydrate dissociation this century are as high as 0.4 million metric tons per year off the Washington coast, or about quadruple the amount of methane from the Deepwater Horizon blowout each year.

Still unknown is where any released methane gas would end up. It could be consumed by bacteria in the seafloor sediment or in the water, where it could cause seawater in that area to become more acidic and oxygen-deprived. Some methane might also rise to the surface, where it would release into the atmosphere as a greenhouse gas, compounding the effects of climate change.
researchers on ship

Evan Solomon (right) and Marta Torres (left, OSU) aboard the UW’s Thomas G. Thompson research vessel in October, with fluid samples from the seafloor that will help answer whether the columns of methane bubbles are due to ocean warming.Robert Cannata / UW

Researchers now hope to verify the calculations with new measurements. For the past few years, curious fishermen have sent UW oceanographers sonar images showing mysterious columns of bubbles. Solomon and Johnson just returned from a cruise to check out some of those sites at depths where Solomon believes they could be caused by warming water.

“Those images the fishermen sent were 100 percent accurate,” Johnson said. “Without them we would have been shooting in the dark.”

Johnson and Solomon are analyzing data from that cruise to pinpoint what’s triggering this seepage, and the fate of any released methane. The recent sightings of methane bubbles rising to the sea surface, the authors note, suggests that at least some of the seafloor gas may reach the surface and vent to the atmosphere.

The research was funded by the National Science Foundation and the U.S. Department of Energy. The other co-author is Robert Harris at Oregon State University.

See the full article here.

Please help promote STEM in your local schools.

Stem Education Coalition

The University of Washington is one of the world’s preeminent public universities. Our impact on individuals, on our region, and on the world is profound — whether we are launching young people into a boundless future or confronting the grand challenges of our time through undaunted research and scholarship. Ranked number 10 in the world in Shanghai Jiao Tong University rankings and educating more than 54,000 students annually, our students and faculty work together to turn ideas into impact and in the process transform lives and our world. For more about our impact on the world, every day.

So what defines us — the students, faculty and community members at the University of Washington? Above all, it’s our belief in possibility and our unshakable optimism. It’s a connection to others, both near and far. It’s a hunger that pushes us to tackle challenges and pursue progress. It’s the conviction that together we can create a world of good. Join us on the journey.

From Caltech: “Caltech Geologists Discover Ancient Buried Canyon in South Tibet”

Caltech

11/20/2014
Kimm Fesenmaier

A team of researchers from Caltech and the China Earthquake Administration has discovered an ancient, deep canyon buried along the Yarlung Tsangpo River in south Tibet, north of the eastern end of the Himalayas. The geologists say that the ancient canyon—thousands of feet deep in places—effectively rules out a popular model used to explain how the massive and picturesque gorges of the Himalayas became so steep, so fast.

The general location of the Himalayan range

This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge—the new discoveries falsify this hypothesis. Credit: Ping Wang

The wide valley floor of the Nyang River, a tributary of the Yarlung Tsangpo. Here, the valley floor of the paleocanyon lies at a depth of about 800 meters below the present-day river.
Credit: Ping Wang

This Google Earth image looks down the Yarlung Tsangpo Valley towards the Namche Barwa (right) and Gyala Peri massifs (left). The confluence with the Nyang River (joining from the right) is shown in the foreground. Here, the valley floor is about 4 kilometers wide and the paleocanyon lies about 800-900 meters below the present-day river.
Credit: Map data: Google, Mapabc.com, DigitalGlobe, and Cnes/Spot Image

“I was extremely surprised when my colleagues, Jing Liu-Zeng and Dirk Scherler, showed me the evidence for this canyon in southern Tibet,” says Jean-Philippe Avouac, the Earle C. Anthony Professor of Geology at Caltech. “When I first saw the data, I said, ‘Wow!’ It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today. That was a big discovery, in my opinion.”

Geologists like Avouac and his colleagues, who are interested in tectonics—the study of the earth’s surface and the way it changes—can use tools such as GPS and seismology to study crustal deformation that is taking place today. But if they are interested in studying changes that occurred millions of years ago, such tools are not useful because the activity has already happened. In those cases, rivers become a main source of information because they leave behind geomorphic signatures that geologists can interrogate to learn about the way those rivers once interacted with the land—helping them to pin down when the land changed and by how much, for example.

World plate tectonics

“In tectonics, we are always trying to use rivers to say something about uplift,” Avouac says. “In this case, we used a paleocanyon that was carved by a river. It’s a nice example where by recovering the geometry of the bottom of the canyon, we were able to say how much the range has moved up and when it started moving.”

The team reports its findings in the current issue of Science.

Last year, civil engineers from the China Earthquake Administration collected cores by drilling into the valley floor at five locations along the Yarlung Tsangpo River. Shortly after, former Caltech graduate student Jing Liu-Zeng, who now works for that administration, returned to Caltech as a visiting associate and shared the core data with Avouac and Dirk Scherler, then a postdoc in Avouac’s group. Scherler had previously worked in the far western Himalayas, where the Indus River has cut deeply into the Tibetan Plateau, and immediately recognized that the new data suggested the presence of a paleocanyon.

Liu-Zeng and Scherler analyzed the core data and found that at several locations there were sedimentary conglomerates, rounded gravel and larger rocks cemented together, that are associated with flowing rivers, until a depth of 800 meters or so, at which point the record clearly indicated bedrock. This suggested that the river once carved deeply into the plateau.

To establish when the river switched from incising bedrock to depositing sediments, they measured two isotopes, beryllium-10 and aluminum-26, in the lowest sediment layer. The isotopes are produced when rocks and sediment are exposed to cosmic rays at the surface and decay at different rates once buried, and so allowed the geologists to determine that the paleocanyon started to fill with sediment about 2.5 million years ago.

The researchers’ reconstruction of the former valley floor showed that the slope of the river once increased gradually from the Gangetic Plain to the Tibetan Plateau, with no sudden changes, or knickpoints. Today, the river, like most others in the area, has a steep knickpoint where it meets the Himalayas, at a place known as the Namche Barwa massif. There, the uplift of the mountains is extremely rapid (on the order of 1 centimeter per year, whereas in other areas 5 millimeters per year is more typical) and the river drops by 2 kilometers in elevation as it flows through the famous Tsangpo Gorge, known by some as the Yarlung Tsangpo Grand Canyon because it is so deep and long.

Combining the depth and age of the paleocanyon with the geometry of the valley, the geologists surmised that the river existed in this location prior to about 3 million years ago, but at that time, it was not affected by the Himalayas. However, as the Indian and Eurasian plates continued to collide and the mountain range pushed northward, it began impinging on the river. Suddenly, about 2.5 million years ago, a rapidly uplifting section of the mountain range got in the river’s way, damming it, and the canyon subsequently filled with sediment.

“This is the time when the Namche Barwa massif started to rise, and the gorge developed,” says Scherler, one of two lead authors on the paper and now at the GFZ German Research Center for Geosciences in Potsdam, Germany.

That picture of the river and the Tibetan Plateau, which involves the river incising deeply into the plateau millions of years ago, differs quite a bit from the typically accepted geologic vision. Typically, geologists believe that when rivers start to incise into a plateau, they eat at the edges, slowly making their way into the plateau over time. However, the rivers flowing across the Himalayas all have strong knickpoints and have not incised much at all into the Tibetan Plateau. Therefore, the thought has been that the rapid uplift of the Himalayas has pushed the rivers back, effectively pinning them, so that they have not been able to make their way into the plateau. But that explanation does not work with the newly discovered paleocanyon.

The team’s new hypothesis also rules out a model that has been around for about 15 years, called tectonic aneurysm, which suggests that the rapid uplift seen at the Namche Barwa massif was triggered by intense river incision. In tectonic aneurysm, a river cuts down through the earth’s crust so fast that it causes the crust to heat up, making a nearby mountain range weaker and facilitating uplift.

The model is popular among geologists, and indeed Avouac himself published a modeling paper in 1996 that showed the viability of the mechanism. “But now we have discovered that the river was able to cut into the plateau way before the uplift happened,” Avouac says, “and this shows that the tectonic aneurysm model was actually not at work here. The rapid uplift is not a response to river incision.”

The other lead author on the paper, Tectonic control of Yarlung Tsangpo Gorge revealed by a buried canyon in Southern Tibet, is Ping Wang of the State Key Laboratory of Earthquake Dynamics, in Beijing, China. Additional authors include Jürgen Mey, of the University of Potsdam, in Germany; and Yunda Zhang and Dingguo Shi of the Chengdu Engineering Corporation, in China. The work was supported by the National Natural Science Foundation of China, the State Key Laboratory for Earthquake Dynamics, and the Alexander von Humboldt Foundation.

See the full article here.

Please help promote STEM in your local schools.

Stem Education Coalition

The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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From Huff Post: “Scientists Venture Deep Inside Mysterious Siberian Crater And Come Back With Incredible Photos”

The Huffington Post

11/13/2014
Macrina Cooper-White

Scientists are closing in on what caused three massive holes to open up mysteriously in northern Siberia last July.

This week a team of Russian researchers roped their way down 34 feet to the bottom of the largest crater and found no evidence of alien beings or meteorites that some people had offered up as possible explanations.

“We managed to go down into the funnel, all was successful,” Vladimir Pushkarev, director of the Russian Center of Arctic Exploration and the leader of the team, told The Siberian Times. “We took all the probes we planned, and made measurements. Now scientists need time to process all the data and only then can they draw conclusions.”

Scroll down for photos.

So what did cause the holes to form? According to Pushkarev, the leading theory is that the holes were created by pockets of gas that exploded underground.

“As of now we don’t see anything dangerous in the sudden appearance of such holes,” he told The Siberian Times, “but we’ve got to study them properly to make absolutely sure we understand the nature of their appearance and don’t need to be afraid about them.”

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

Vladimir Pushkarev/The Siberian Times

See the full article here.

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From livescience: “Crater Hunters Find New Clues to Ancient Impact Storm”

October 31, 2014
Becky Oskin

Back when Wisconsin and western Russia once shared an address south of the equator, a violent collision in the asteroid belt blasted Earth with meteorites.

A meteor crater in northern Quebec, Canada.
Credit: NASA Earth Observatory

The space rock smashup showered Earth with up to 100 times more meteorites than today’s rate (a rock the size of a football field hits the planet about every 10,000 years). Yet, only a dozen or so impact craters have been found from the ancient bombardment 470 million years ago, during the Ordovician Period. Most are in North America, Sweden and western Russia. There are only about 185 known impact craters on Earth of any age, while the moon has more than 100,000.

But the number of Ordovician craters may soon take off. That’s because it’s easier and cheaper than ever to hunt down evidence that confirms an impact. The clinchers include shocked minerals, deformed rocks and structural features that match other craters.

“Google Earth images are not good enough to identify an impact structure,” noted planetary geologist Christian Köeberl on Oct. 22, at the Geological Society of America’s annual meeting in Vancouver, British Columbia. During the Vancouver meeting, researchers presented new clues that bring suspected craters in Wisconsin, Kentucky and Tennessee closer to official listings as Ordovician impact craters.

The three enigmatic structures retain their circular shape, but have lost most of their original features through erosion. In the last century, quarrying has also slowly dismantled the Wisconsin crater. Only the central uplift seems to persist. When a meteorite hits, the impact’s force causes the underlying rock to rebound upward, leaving a topographic high in the center of the crater.

In each state, researchers looked for traces of minerals shattered or heated by the impact. So far, no one has found one of the smoking guns in crater research: shatter cones, the finely fractured rocks created when the shock wave travels through the ground. The fractures are often arranged in a conical shape, like an ice cream cone.

Three little craters

Fractured rocks exposed in a quarry in Brussels Hill, Wisconsin. Credit: Emily Zawacki

But even without a smoking gun, at Brussels Hill in Door County, Wisconsin, a meteorite impact is the best explanation for the perfectly round, 130-foot-tall (40 meters) hill, said Emily Zawacki, an undergraduate at Lawrence University in Appleton, Wisconsin. The flat-topped peak is filled with fractured blocks of Cambrian sandstone that should lie some 1,300 feet below the younger carbonate rocks. The fragmented rocks all tilt toward the center of the hill, and a series of faults radiate outward from its center.

The evidence all points to a deeply eroded impact crater, Zawacki said. “This is a highly disturbed area in otherwise flat-lying stratigraphy,” Zawacki said. “It very clearly is anomalous and we feel a meteoritic impact best explains it.”

In the middle of Tennessee, the Howell Structure has confounded geologists for decades. The bowl-shaped basin is about the same diameter as Brussels Hill (about 1.2 miles, or 2 km). In this case, however, the suspected crater is weaker than the surrounding rocks, creating a depression. A pile of fragmented carbonate and other craterlike features suggests an impact origin.

Keith Milam, a professor at Ohio University in Athens, recently uncovered a rare trove of rock cores drilled at Howell in the 1960s. John Bensko, a retired lunar geologist from NASA’s Marshall Space Flight Center, provided the 15 segments. Bensko oversaw the testing of drilling equipment intended for the canceled Apollo 18 program. The first tests on the rock cores suggest the fragmented carbonate rocks were shocked by a meteorite impact, Milam reported at the Vancouver meeting.

Finally, the Jeptha Knob structure in Kentucky is a site that stands out on Google Earth and just needs the right mineral evidence to certify its impact origin. “I don’t think you can say for sure this is an impact structure yet,” said Eric Gibbs, an undergraduate at Ohio University in Athens. Gibbs is testing the X-ray diffraction pattern produced by minerals from the crater. The pattern shortens and widens with increasing shock, he said.

A partial map of Ordovician continents and impact craters. Credit: Jens Ormö et al., Scientific Reports

The initial tests, presented at the Vancouver geology meeting, support an impact origin for the hill. Jeptha Knob is the highest point in Kentucky’s Bluegrass Region, rising some 300 feet (90 m) above the surrounding farms. The round crater is ringed by faults and busted-up Ordovician limestone, but topped by flat layers of younger carbonate rocks.

The apparent alignment of many of these craters makes it seem that some coincidence favored Earth’s tropical latitudes during the big Ordovician bombardment.

At the time, North America was flipped backward and sitting across the equator. The Baltica continent — western Russia, Sweden and Finland — was just to the south. There are six confirmed Ordovician craters in the central United States and more in the middle of Canada. There are five confirmed craters in Sweden; and this month a double crater was identified in central Sweden at Lockne and Malinga, according to a study published Oct. 24 in the journal Scientific Reports. Who knows how many more are buried under the protective limestones and shales of the huge Ordovician seas?

See the full article, with additional material, here.

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From Caltech: “Unexpected Findings Change the Picture of Sulfur on the Early Earth”

Caltech

11/07/2014
Kimm Fesenmaier

Scientists believe that until about 2.4 billion years ago there was little oxygen in the atmosphere—an idea that has important implications for the evolution of life on Earth. Evidence in support of this hypothesis comes from studies of sulfur isotopes preserved in the rock record. But the sulfur isotope story has been uncertain because of the lack of key information that has now been provided by a new analytical technique developed by a team of Caltech geologists and geochemists. The story that new information reveals, however, is not what most scientists had expected.

2.5 billion-year-old sedimentary strata exposed in the Northern Cape Province of South Africa. Credit: Jess Adkins/Caltech

Reef mounds formed of radiating calcium carbonate crystal fans on the Archean seafloor. Credit: Jess Adkins/Caltech

Cross-section view of calcium carbonate crystal fans that grew on the seafloor circa 2.6 billion years ago. Credit: Jess Adkins/Caltech

“Our new technique is 1,000 times more sensitive for making sulfur isotope measurements,” says Jess Adkins, professor of geochemistry and global environmental science at Caltech. “We used it to make measurements of sulfate groups dissolved in carbonate minerals deposited in the ocean more than 2.4 billion years ago, and those measurements show that we have been thinking about this part of the sulfur cycle and sulfur isotopes incorrectly.”

The team describes their results in the November 7 issue of the journal Science. The lead author on the paper is Guillaume Paris, an assistant research scientist at Caltech.

Nearly 15 years ago, a team of geochemists led by researchers at UC San Diego discovered there was something peculiar about the sulfur isotope content of rocks from the Archean era, an interval that lasted from 3.8 billion to about 2.4 billion years ago. In those ancient rocks, the geologists were analyzing the abundances of stable isotopes of sulfur.

When sulfur is involved in a reaction—such as microbial sulfate reduction, a way for microbes to eat organic compounds in the absence of oxygen—its isotopes are usually fractionated, or separated, from one another in proportion to their differences in mass. That is, 34S gets fractionated from 32S about twice as much as 33S gets fractionated from 32S. This process is called mass-dependent fractionation, and, scientists have found that it dominates in virtually all sulfur processes operating on Earth’s surface for the last 2.4 billion years.

However, in older rocks from the Archean era (i.e., older than 2.4 billion years), the relative abundances of sulfur isotopes do not follow the same mass-related pattern, but instead show relative enrichments or deficiencies of 33S relative to 34S. They are said to be the product of mass-independent fractionation (MIF).

The widely accepted explanation for the occurrence of MIF is as follows. Billions of years ago, volcanism was extremely active on Earth, and all those volcanoes spewed sulfur dioxide high into the atmosphere. At that time, oxygen existed at very low levels in the atmosphere, and therefore ozone, which is produced when ultraviolet radiation strikes oxygen, was also lacking. Today, ozone prevents ultraviolet light from reaching sulfur dioxide with the energy needed to fractionate sulfur, but on the early Earth, that was not the case, and MIF is the result. Researchers have been able to reproduce this effect in the lab by shining lasers onto sulfur dioxide and producing MIF.

Geologists have also measured the sulfur isotopic composition of sedimentary rocks dating to the Archean era, and found that sulfides—sulfur-bearing compounds such as pyrite (FeS2)—include more 33S than would be expected based on normal mass-dependent processes. But if those minerals are enriched in 33S, other minerals must be correspondingly lacking in the isotope. According to the leading hypothesis, those 33S-deficient minerals should be sulfates—oxidized sulfur-bearing compounds—that were deposited in the Archean ocean.

“That idea was put forward on the basis of experiment. To test the hypothesis, you’d need to check the isotope ratios in sulfate salts (minerals such as gypsum), but those don’t really exist in the Archean rock record since there was very little oxygen around,” explains Woody Fischer, professor of geobiology at Caltech and a coauthor on the new paper. “But there are trace amounts of sulfate that got trapped in carbonate minerals in seawater.”

However, because those sulfates are present in such small amounts, no one has been able to measure well their isotopic composition. But using a device known as a multicollector inductively-coupled mass spectrometer to precisely measure multiple sulfur isotopes, Adkins and his colleague Alex Sessions, a professor of geobiology, developed a method that is sensitive enough to measure the isotopic composition of about 10 nanomoles of sulfate in just a few tens of milligrams of carbonate material.

The authors used the method to measure the sulfate content of carbonates from an ancient carbonate platform preserved in present-day South Africa, an ancient version of the depositional environments found in the Bahamas today. Analyzing the samples, which spanned 70 million years and a variety of marine environments, the researchers found exactly the opposite of what had been predicted: the sulfates were actually enriched by 33S rather than lacking in it.

“Now, finally, we’re looking at this sulfur cycle and the sulfur isotopes correctly,” Adkins says.

What does this mean for the atmospheric conditions of the early Earth? “Our findings underscore that the oxygen concentrations in the early atmosphere could have been incredibly low,” Fischer says.

Knowledge of sulfate isotopes changes how we understand the role of biology in the sulfur cycle, he adds. Indeed, the fact that the sulfates from this time period have the same isotopic composition as sulfide minerals suggests that the sulfides may be the product of microbial processes that reduced seawater sulfate to sulfide (which later precipitated in sediments in the form of pyrite). Previously, scientists thought that all of the isotope fractionation could be explained by inorganic processes alone.

In a second paper also in the November 7 issue of Science, Paris, Adkins, Sessions, and colleagues from a number of institutions around the world report on related work in which they measured the sulfates in Indonesia’s Lake Matano, a low-sulfate analog of the Archean ocean.

At about 100 meters depth, the bacterial communities in Lake Matano begin consuming sulfate rather than oxygen, as do most microbial communities, yielding sulfide. The researchers measured the sulfur isotopes within the sulfates and sulfides in the lake water and sediments and found that despite the low concentrations of sulfate, a lot of mass-dependent fractionation was taking place. The researchers used the data to build a model of the lake’s sulfur cycle that could produce the measured fractionation, and when they applied their model to constrain the range of concentrations of sulfate in the Archean ocean, they found that the concentration was likely less than 2.5 micromolar, 10,000 times lower than the modern ocean.

“At such low concentration, all the isotopic variability starts to fit,” says Adkins. “With these two papers, we were able to come at the same problem in two ways—by measuring the rocks dating from the Archean and by looking at a model system today that doesn’t have much sulfate—and they point toward the same answer: the sulfate concentration was very low in the Archean ocean.”

Samuel M. Webb of the Stanford Synchrotron Radiation Lightsource is also an author on the paper, “Neoarchean carbonate-associated sulfate records positive Δ33S anomalies.” The work was supported by funding from the National Science Foundation’s Division of Earth Sciences, the Henry and Camille Dreyfus Foundation’s Postdoctoral Program in Environmental Chemistry, and the David and Lucile Packard Foundation.

Paris is also a co-lead author on the second paper, Sulfate was a trace constituent of Archean seawater. Additional authors on that paper are Sean Crowe and CarriAyne Jones of the University of British Columbia and the University of Southern Denmark; Sergei Katsev of the University of Minnesota Duluth; Sang-Tae Kim of McMaster University; Aubrey Zerkle of the University of St. Andrews; Sulung Nomosatryo of the Indonesian Institute of Sciences; David Fowle of the University of Kansas; James Farquhar of the University of Maryland, College Park; and Donald Canfield of the University of Southern Denmark. Funding was provided by an Agouron Institute Geobiology Fellowship and a Natural Sciences and Engineering Research Council of Canada Postdoctoral Fellowship, as well as by the Danish National Research Foundation and the European Research Council.

See the full article here.

The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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