Geologists discover ancient buried canyon in South Tibet

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. -  Ping Wang
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. – Ping Wang

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.

“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.

“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.”

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The other lead author on the paper, “Tectonic control of the Yarlung Tsangpo Gorge, revealed by a 2.5 Myr old 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.

Re-learning how to read a genome

New research has revealed that the initial steps of reading DNA are actually remarkably similar at both the genes that encode proteins (here, on the right) and regulatory elements (on the left). The main differences seem to occur after this initial step. Gene messages are long and stable enough to ensure that genes become proteins, whereas regulatory messages are short and unstable, and are rapidly 'cleaned up' by the cell. -  Adam Siepel, Cold Spring Harbor Laboratory
New research has revealed that the initial steps of reading DNA are actually remarkably similar at both the genes that encode proteins (here, on the right) and regulatory elements (on the left). The main differences seem to occur after this initial step. Gene messages are long and stable enough to ensure that genes become proteins, whereas regulatory messages are short and unstable, and are rapidly ‘cleaned up’ by the cell. – Adam Siepel, Cold Spring Harbor Laboratory

There are roughly 20,000 genes and thousands of other regulatory “elements” stored within the three billion letters of the human genome. Genes encode information that is used to create proteins, while other genomic elements help regulate the activation of genes, among other tasks. Somehow all of this coded information within our DNA needs to be read by complex molecular machinery and transcribed into messages that can be used by our cells.

Usually, reading a gene is thought to be a lot like reading a sentence. The reading machinery is guided to the start of the gene by various sequences in the DNA – the equivalent of a capital letter – and proceeds from left to right, DNA letter by DNA letter, until it reaches a sequence that forms a punctuation mark at the end. The capital letter and punctuation marks that tell the cell where, when, and how to read a gene are known as regulatory elements.

But scientists have recently discovered that genes aren’t the only messages read by the cell. In fact, many regulatory elements themselves are also read and transcribed into messages, the equivalent of pronouncing the words “capital letter,” “comma,” or “period.” Even more surprising, genes are read bi-directionally from so-called “start sites” – in effect, generating messages in both forward and backward directions.

With all these messages, how does the cell know which one encodes the information needed to make a protein? Is there something different about the reading process at genes and regulatory elements that helps avoid confusion? New research, published today in Nature Genetics, has revealed that the initial steps of the reading process itself are actually remarkably similar at both genes and regulatory elements. The main differences seem to occur after this initial step, in the length and stability of the messages. Gene messages are long and stable enough to ensure that genes becomes proteins, whereas regulatory messages are short and unstable, and are rapidly “cleaned up” by the cell.

To make the distinction, the team, which was co-led by CSHL Professor Adam Siepel and Cornell University Professor John Lis, looked for differences between the initial reading processes at genes and a set of regulatory elements called enhancers. “We took advantage of highly sensitive experimental techniques developed in the Lis lab to measure newly made messages in the cell,” says Siepel. “It’s like having a new, more powerful microscope for observing the process of transcription as it occurs in living cells.”

Remarkably, the team found that the reading patterns for enhancer and gene messages are highly similar in many respects, sharing a common architecture. “Our data suggests that the same basic reading process is happening at genes and these non-genic regulatory elements,” explains Siepel. “This points to a unified model for how DNA transcription is initiated throughout the genome.”

Working together, the biochemists from Lis’s laboratory and the computer jockeys from Siepel’s group carefully compared the patterns at enhancers and genes, combining their own data with vast public data sets from the NIH’s Encyclopedia of DNA Elements (ENCODE) project. “By many different measures, we found that the patterns of transcription initiation are essentially the same at enhancers and genes,” says Siepel. “Most RNA messages are rapidly targeted for destruction, but the messages at genes that are read in the right direction – those destined to be a protein – are spared from destruction.” The team was able to devise a model to mathematically explain the difference between stable and unstable transcripts, offering insight into what defines a gene. According to Siepel, “Our analysis shows that the ‘code’ for stability is, in large part, written in the DNA, at enhancers and genes alike.”

This work has important implications for the evolutionary origins of new genes, according to Siepel. “Because DNA is read in both directions from any start site, every one of these sites has the potential to generate two protein-coding genes with just a few subtle changes. The genome is full of potential new genes.”

This work was supported by the National Institutes of Health.

“Analysis of transcription start sites from nascent RNA identifies a unified architecture of initiation regions at mammalian promoters and enhancers.” appears online in Nature Genetics on November 10, 2014. The authors are: Leighton Core, André Martins, Charles Danko, Colin Waters, Adam Siepel, and John Lis. The paper can be obtained online at: http://dx.doi.org/10.1038/ng.3142

About Cold Spring Harbor Laboratory

Founded in 1890, Cold Spring Harbor Laboratory (CSHL) has shaped contemporary biomedical research and education with programs in cancer, neuroscience, plant biology and quantitative biology. CSHL is ranked number one in the world by Thomson Reuters for the impact of its research in molecular biology and genetics. The Laboratory has been home to eight Nobel Prize winners. Today, CSHL’s multidisciplinary scientific community is more than 600 researchers and technicians strong and its Meetings & Courses program hosts more than 12,000 scientists from around the world each year to its Long Island campus and its China center. For more information, visit http://www.cshl.edu.

Asian monsoon much older than previously thought

University of Arizona geoscientist Alexis Licht (bottom left) and his colleagues from the French-Burmese Paleontological Team led by Jean-Jacques Jaeger of the University of Poitiers, France (center with hiking staff) used fossils they collected in Myanmar to figure out that the Asian monsoon started at least 40 million years ago. -  French-Burmese Paleontological Team 2012
University of Arizona geoscientist Alexis Licht (bottom left) and his colleagues from the French-Burmese Paleontological Team led by Jean-Jacques Jaeger of the University of Poitiers, France (center with hiking staff) used fossils they collected in Myanmar to figure out that the Asian monsoon started at least 40 million years ago. – French-Burmese Paleontological Team 2012

The Asian monsoon already existed 40 million years ago during a period of high atmospheric carbon dioxide and warmer temperatures, reports an international research team led by a University of Arizona geoscientist.

Scientists thought the climate pattern known as the Asian monsoon began 22-25 million years ago as a result of the uplift of the Tibetan Plateau and the Himalaya Mountains.

“It is surprising,” said lead author Alexis Licht, now a research associate in the UA department of geosciences. “People thought the monsoon started much later.”

The monsoon, the largest climate system in the world, governs the climate in much of mainland Asia, bringing torrential summer rains and dry winters.

Co-author Jay Quade, a UA professor of geosciences, said, “This research compellingly shows that a strong Asian monsoon system was in place at least by 35-40 million years ago.”

The research by Licht and his colleagues shows the earlier start of the monsoon occurred at a time when atmospheric CO2 was three to four times greater than it is now. The monsoon then weakened 34 million years ago when atmospheric CO2 then decreased by 50 percent and an ice age occurred.

Licht said the study is the first to show the rise of the monsoon is as much a result of global climate as it is a result of topography. The team’s paper is scheduled for early online publication in the journal Nature on Sept. 14.

“This finding has major consequences for the ongoing global warming,” he said. “It suggests increasing the atmospheric CO2 will increase the monsoonal precipitation significantly.”

Unraveling the monsoon’s origins required contributions from three different teams of scientists that were independently studying the environment of 40 million years ago.

All three investigations showed the monsoon climate pattern occurred 15 million years earlier than previously thought. Combining different lines of evidence from different places strengthened the group’s confidence in the finding, Licht said. The climate modeling team also linked the development of the monsoon to the increased CO2 of the time.

Licht and his colleagues at Poitiers and Nancy universities in France examined snail and mammal fossils in Myanmar. The group led by G. Dupont-Nivet and colleagues at Utrecht University in the Netherlands studied lake deposits in Xining Basin in central China. J.-B. Ladant and Y. Donnadieu of the Laboratory of Sciences of the Climate and Environment (LSCE) in Gif-sur-Yvette, France, created climate simulations of the Asian climate 40 million years ago.

A complete list of authors of the group’s publication, “Asian monsoons in a late Eocene greenhouse world,” is at the bottom of this release, as is a list of funding sources.

Licht didn’t set out to study the origin of the monsoon.

He chose his study site in Myanmar because the area was rich in mammal fossils, including some of the earliest ancestors of modern monkeys and apes. The research, part of his doctoral work at the University of Poitiers, focused on understanding the environments those early primates inhabited. Scientists thought those primates had a habitat like the current evergreen tropical rain forests of Borneo, which do not have pronounced differences between wet and dry seasons.

To learn about the past environment, Licht analyzed 40-million-year-old freshwater snail shells and teeth of mammals to see what types of oxygen they contained. The ratio of two different forms of oxygen, oxygen-18 and oxygen-16, shows whether the animal lived in a relatively wet climate or an arid one.

“One of the goals of the study was to document the pre-monsoonal conditions, but what we found were monsoonal conditions,” he said.

To his surprise, the oxygen ratios told an unexpected story: The region had a seasonal pattern very much like the current monsoon – dry winters and very rainy summers.

“The early primates of Myanmar lived under intense seasonal stress – aridity and then monsoons,” he said. “That was completely unexpected.”

The team of researchers working in China found another line of evidence pointing to the existence of the monsoon about 40 million years ago. The monsoon climate pattern generates winter winds that blow dust from central Asia and deposits it in thick piles in China. The researchers found deposits of such dust dating back 41 million years ago, indicating the monsoon had occurred that long ago.

The third team’s climate simulations indicated strong Asian monsoons 40 million years ago. The simulations showed the level of atmospheric CO2 was connected to the strength of the monsoon, which was stronger 40 million years ago when CO2 levels were higher and weakened 34 million years ago when CO2 levels dropped.

Licht’s next step is to investigate how geologically short-term increases of atmospheric CO2 known as hyperthermals affected the monsoon’s behavior 40 million years ago.

“The response of the monsoon to those hyperthermals could provide interesting analogs to the ongoing global warming,” he said.

Sea-level spikes, volcanic risk, volcanos cause drought

Unforeseen, short-term increases in sea level caused by strong winds, pressure changes and fluctuating ocean currents can cause more damage to beaches on the East Coast over the course of a year than a powerful hurricane making landfall, according to a new study. The new research suggests that these sea-level anomalies could be more of a threat to coastal homes and businesses than previously thought, and could become higher and more frequent as a result of climate change, according to a new study accepted for publication in Geophysical Research Letters, a journal of the American Geophysical Union.

From this week’s Eos: Assessing Volcanic Risk in Saudi Arabia: An Integrated Approach


The Kingdom of Saudi Arabia has numerous large volcanic fields, known locally as “harrats.” The largest of these, Harrat Rahat, produced a basaltic fissure eruption in 1256 A.D. with lava flows traveling within 20 kilometers of the city Al-Madinah, which has a current population of 1.5 million plus an additional 3 million pilgrims annually. With more than 950 visible vents and periodic seismic swarms, an understanding of the risk of future eruptions in this volcanic field is vital. The Volcanic Risk in Saudi Arabia (VORISA) project was developed as a multidisciplinary international research collaboration that integrates geological, geophysical, hazard, and risk studies in this important area.

From AGU’s journals: Large volcanic eruptions cause drought in eastern China


In most cases, the annual East Asian Monsoon brings heavy rains and widespread flooding to southeast China and drought conditions to the northeast. At various points throughout history, however, large volcanic eruptions have upset the regular behavior of the monsoon.

Sulfate aerosols injected high into the atmosphere by powerful eruptions can lower the land-sea temperature contrast that powers the monsoon circulation. How this altered aerosol forcing affects precipitation is not entirely clear, however, as climate models do not always agree with observations of the nature and scale of the effect.

Using two independent records of historical volcanic activity along with two different measures of rainfall, including one 3,000-year long record derived from local flood and drought observations, Zhuo et al. analyzes how large volcanic eruptions changed the conditions on the ground for the period 1368 to 1911. Understanding the effect of sulfate aerosols on monsoon behavior is particularly important now, as researchers explore aerosol seeding as a means of climate engineering.

The authors find that large Northern Hemispheric volcanic eruptions cause strong droughts in much of eastern China. The drought begins in the north in the second or third summer following an eruption and slowly moves southward over the next 2 to 3 years. They find that the severity of the drought scales with the amount of aerosol injected into the atmosphere, and that it takes 4 to 5 years for precipitation to recover. The drying pattern agrees with observations from three large modern eruptions.

China’s northeast is the country’s major grain-producing region. The results suggest that any geoengineering schemes meant to mimic the effect of a large volcanic eruption could potentially trigger devastating consequences for China’s food supply.

Burrowing animals may have been key to stabilizing Earth’s oxygen

This image depicts a 530-million-year-old fossil of burrow activity in sediment. -  Martin Brasier, University of Oxford
This image depicts a 530-million-year-old fossil of burrow activity in sediment. – Martin Brasier, University of Oxford

Evolution of the first burrowing animals may have played a major role in stabilizing the Earth’s oxygen reservoir, according to a new study in Nature Geoscience.

Around 540 million years ago, the first burrowing animals evolved. When these worms began to mix up the ocean floor’s sediments (a process known as bioturbation), their activity came to significantly influence the ocean’s phosphorus cycle and as a result, the amount of oxygen in Earth’s atmosphere.

“Our research is an attempt to place the spread of animal life in the context of wider biogeochemical cycles, and we conclude that animal activity had a decreasing impact on the global oxygen reservoir and introduced a stabilizing effect on the connection between the oxygen and phosphorus cycles”, says lead author Dr. Richard Boyle from the Nordic Center for Earth Evolution (NordCEE) at the University of Southern Denmark.

The computer modelling study by Dr. Richard Boyle and colleagues from Denmark, Germany, China and the UK, published in Nature Geoscience, links data from the fossil record to well established connections between the phosphorus and oxygen cycles.

Marine organic carbon burial is a source of oxygen to the atmosphere, and its rate is proportional to the amount of phosphate in the oceans. This means that (over geologic timescales) anything that decreases the size of the ocean phosphate reservoir also decreases oxygen. The study focuses on one such removal process, burial of phosphorus in the organic matter in ocean sediments.

The authors hypothesize the following sequence of events: Around 540 million years ago, the evolution of the first burrowing animals significantly increased the extent to which oxygenated waters came into contact with ocean sediments. Exposure to oxygenated conditions caused the bacteria that inhabit such sediments to store phosphate in their cells (something that is observed in modern day experiments). This caused an increase in phosphorus burial in sediments that had been mixed up by burrowing animals. This in turn triggered decreases in marine phosphate concentrations, productivity, organic carbon burial and ultimately oxygen. Because an oxygen decrease was initiated by something requiring oxygen (i.e. the activity burrowing animals) a net negative feedback loop was created.

Boyle states: “It has long been appreciated that organic phosphorus burial is greater from the kind of well oxygenated, well-mixed sediments that animals inhabit, than from poorly mixed, low oxygen “laminated” sediments. The key argument we make in this paper is that this difference is directly attributable to bioturbation. This means that (1) animals are directly involved in an oxygen-regulating cycle or feedback loop that has previously been overlooked, and (2) we can directly test the idea (despite the uncertainties associated with looking so far back in time) by looking for a decrease in ocean oxygenation in conjunction with the spread of bioturbation. My colleague, Dr Tais Dahl from University of Copenhagen, compiled data on ocean metals with oxygen-sensitive burial patterns, which does indeed suggest such an oxygen decrease as bioturbation began – confirming the conclusions of the modelling. It is our hope that wider consideration of this feedback loop and the timing of its onset, will improve our understanding of the extent to which Earth’s atmosphere-ocean oxygen reservoir is regulated.”

Co-author Professor Tim Lenton of the University of Exeter adds: “We already think this cycle was key to helping stabilise atmospheric oxygen during the Phanerozoic (the last 542 million years) – and that oxygen stability is a good thing for the evolution of plants and animals. What is new in this study is it attributes the oxygen stabilisation to biology – the presence or absence of animals stirring up the ocean sediments.”

Earlier this year, researchers from the Nordic Center for Earth Evolution showed that early animals may have needed surprisingly little oxygen to grow, supporting the theory that rising oxygen levels were not crucial for animal life to evolve on Earth.

Geologists prove early Tibetan Plateau was larger than previously thought

This is Syracuse University professor Gregory Hoke. -  Syracuse University
This is Syracuse University professor Gregory Hoke. – Syracuse University

Earth scientists in Syracuse University’s College of Arts and Sciences have determined that the Tibetan Plateau-the world’s largest, highest, and flattest plateau-had a larger initial extent than previously documented.

Their discovery is the subject of an article in the journal Earth and Planetary Science Letters (Elsevier, 2014).

Gregory Hoke, assistant professor of Earth sciences, and Gregory Wissink, a Ph.D. student in his lab, have co-authored the article with Jing Liu-Zeng, director of the Division of Neotectonics and Geomorphology at the Institute for Geology, part of the China Earthquake Administration; Michael Hren, assistant professor of chemistry at the University of Connecticut; and Carmala Garzione, professor and chair of Earth and environmental sciences at the University of Rochester.

“We’ve determined the elevation history of the southeast margin of the Tibetan Plateau,” says Hoke, who specializes in the interplay between the Earth’s tectonic and surface processes. “By the Eocene epoch (approximately 40 million years ago), the southern part of the plateau extended some 600 miles more to the east than previously documented. This discovery upends a popular model for plateau formation.”

Known as the “Roof of the World,” the Tibetan Plateau covers more than 970,000 square miles in Asia and India and reaches heights of over 15,000 feet. The plateau also contains a host of natural resources, including large mineral deposits and tens of thousands of glaciers, and is the headwaters of many major drainage basins.

Hoke says he was attracted to the topography of the plateau’s southeast margin because it presented an opportunity to use information from minerals formed at the Earth’s surface to infer what happened below them in the crust.

“The tectonic and topographic evolution of the southeast margin has been the subject of considerable controversy,” he says. “Our study provides the first quantitative estimate of the past elevation of the eastern portions of the plateau.”

Historically, geologists have thought that lower crustal flow- a process by which hot, ductile rock material flows from high- to low-pressure zones-helped elevate parts of the plateau about 20 million years ago. (This uplift model has also been used to explain watershed reorganization among some of the world’s largest rivers, including the Yangtze in China.)

But years of studying rock and water samples from the plateau have led Hoke to rethink the area’s history. For starters, his data indicates that the plateau has been at or near its present elevation since the Eocene epoch. Moreover, surface uplift in the southernmost part of the plateau-in and around southern China and northern Vietnam-has been historically small.

“Surface uplift, caused by lower crustal flow, doesn’t explain the evolution of regional river networks,” says Hoke, referring to the process by which a river drainage system is diverted, or captured, from its own bed into that of a neighboring bed. “Our study suggests that river capture and drainage reorganization must have been the result of a slip on the major faults bounding the southeast plateau margin.”

Hoke’s discovery not only makes the plateau larger than previously thought, but also suggests that some of the topography is millions of years younger.

“Our data provides the first direct documentation of the magnitude and geographic extent of elevation change on the southeast margin of the Tibetan Plateau, tens of millions years ago,” Hoke adds. “Constraining the age, spatial extent, and magnitude of ancient topography has a profound effect on how we understand the construction of mountain ranges and high plateaus, such as those in Tibet and the Altiplano region in Bolivia.”

The Goldilocks principle: New hypothesis explains earth’s continued habitability

Researchers from USC and Nanjing University in China have documented evidence suggesting that part of the reason that the Earth has become neither sweltering like Venus nor frigid like Mars lies with a built-in atmospheric carbon dioxide regulator – the geologic cycles that churn up the planet’s rocky surface.

Scientists have long known that “fresh” rock pushed to the surface via mountain formation effectively acts as a kind of sponge, soaking up the greenhouse gas CO2. Left unchecked, however, that process would simply deplete atmospheric CO2 levels to a point that would plunge the Earth into an eternal winter within a few million years during the formation of large mountain ranges like the Himalayas – which has clearly not happened.

And while volcanoes have long been pointed to as a source of carbon dioxide, alone they cannot balance out the excess uptake of carbon dioxide by large mountain ranges. Instead, it turns out that “fresh” rock exposed by uplift also emits carbon through a chemical weathering process, which replenishes the atmospheric carbon dioxide at a comparable rate.

“Our presence on Earth is dependent upon this carbon cycle. This is why life is able to survive,” said Mark Torres, lead author of a study disclosing the findings that appears in Nature on March 20. Torres, a doctoral fellow at the USC Dornsife College of Letters, Arts and Sciences, and a fellow at the Center for Dark Energy Biosphere Investigations (C-DEBI), collaborated with Joshua West, professor of Earth Sciences at USC Dornsife, and Gaojun Li of Nanjing University in China.

While human-made atmospheric carbon dioxide increases are currently driving significant changes in the Earth’s climate, the geologic system has kept things balanced for million of years.

“The Earth is a bit like a big, natural recycler,” West said. Torres and West studied rocks taken from the Andes mountain range in Peru and found that weathering processes affecting rocks released far more carbon than previously estimated, which motivated them to consider the global implications of CO2 release during mountain formation.

The researchers noted that rapid erosion in the Andes unearths abundant pyrite – the shiny mineral known as “fool’s gold” because of its deceptive appearance – and its chemical breakdown produces acids that release CO2 from other minerals. These observations motivated them to consider the global implications of CO2 release during mountain formation.

Like many other large mountain ranges, such as the great Himalayas, the Andes began to form during the Cenozoic period, which began about 60 million years ago and happened to coincide with a major perturbation in the cycling of atmospheric carbon dioxide. Using marine records of the long-term carbon cycle, Torres, West, and Li reconstructed the balance between CO2 release and uptake caused by the uplift of large mountain ranges and found that the release of CO2 release by rock weathering may have played a large, but thus far unrecognized, role in regulating the concentration of atmospheric carbon dioxide over the last roughly 60 million years.

Giant mass extinction may have been quicker than previously thought

The largest mass extinction in the history of animal life occurred some 252 million years ago, wiping out more than 96 percent of marine species and 70 percent of life on land – including the largest insects known to have inhabited the Earth. Multiple theories have aimed to explain the cause of what’s now known as the end-Permian extinction, including an asteroid impact, massive volcanic eruptions, or a cataclysmic cascade of environmental events. But pinpointing the cause of the extinction requires better measurements of how long the extinction period lasted.

Now researchers at MIT have determined that the end-Permian extinction occurred over 60,000 years, give or take 48,000 years – practically instantaneous, from a geologic perspective. The new timescale is based on more precise dating techniques, and indicates that the most severe extinction in history may have happened more than 10 times faster than scientists had previously thought.

“We’ve got the extinction nailed in absolute time and duration,” says Sam Bowring, the Robert R. Shrock Professor of Earth and Planetary Sciences at MIT. “How do you kill 96 percent of everything that lived in the oceans in tens of thousands of years? It could be that an exceptional extinction requires an exceptional explanation.”

In addition to establishing the extinction’s duration, Bowring, graduate student Seth Burgess, and a colleague from the Nanjing Institute of Geology and Paleontology also found that, 10,000 years before the die-off, the oceans experienced a pulse of light carbon, which likely reflects a massive addition of carbon dioxide to the atmosphere. This dramatic change may have led to widespread ocean acidification and increased sea temperatures by 10 degrees Celsius or more, killing the majority of sea life.

But what originally triggered the spike in carbon dioxide? The leading theory among geologists and paleontologists has to do with widespread, long-lasting volcanic eruptions from the Siberian Traps, a region of Russia whose steplike hills are a result of repeated eruptions of magma. To determine whether eruptions from the Siberian Traps triggered a massive increase in oceanic carbon dioxide, Burgess and Bowring are using similar dating techniques to establish a timescale for the Permian period’s volcanic eruptions that are estimated to have covered over five million cubic kilometers.

“It is clear that whatever triggered extinction must have acted very quickly,” says Burgess, the lead author of a paper that reports the results in this week’s Proceedings of the National Academy of Sciences, “fast enough to destabilize the biosphere before the majority of plant and animal life had time to adapt in an effort to survive.”

Pinning dates on an extinction


In 2006, Bowring and his students made a trip to Meishan, China, a region whose rock formations bear evidence of the end-Permian extinction; geochronologists and paleontologists have flocked to the area to look for clues in its layers of sedimentary rock. In particular, scientists have focused on a section of rock that is thought to delineate the end of the Permian, and the beginning of the Triassic, based on evidence such as the number of fossils found in surrounding rock layers.

Bowring sampled rocks from this area, as well as from nearby alternating layers of volcanic ash beds and fossil-bearing rocks. After analyzing the rocks in the lab, his team reported in 2011 that the end-Permian likely lasted less than 200,000 years. However, this timeframe still wasn’t precise enough to draw any conclusions about what caused the extinction.

Now, the team has revised its estimates using more accurate dating techniques based on a better understanding of uncertainties in timescale measurements.

With this knowledge, Bowring and his colleagues reanalyzed rock samples collected from five volcanic ash beds at the Permian-Triassic boundary. The researchers pulverized rocks and separated out tiny zircon crystals containing a mix of uranium and lead. They then isolated uranium from lead, and measured the ratios of both isotopes to determine the age of each rock sample.

From their measurements, the researchers determined a much more precise “age model” for the end-Permian extinction, which now appears to have lasted about 60,000 years – with an uncertainty of 48,000 years – and was immediately preceded by a sharp increase in carbon dioxide in the oceans.

‘Spiraling toward the truth’


The new timeline adds weight to the theory that the extinction was triggered by massive volcanic eruptions from the Siberian Traps that released volatile chemicals, including carbon dioxide, into the atmosphere and oceans. With such a short extinction timeline, Bowring says it is possible that a single, catastrophic pulse of magmatic activity triggered an almost instantaneous collapse of all global ecosystems.

To confirm whether the Siberian Traps are indeed the extinction’s smoking gun, Burgess and Bowring plan to determine an equally precise timeline for the Siberian Traps eruptions, and will compare it to the new extinction timeline to see where the two events overlap. The researchers will investigate additional areas in China to see if the duration of the extinction can be even more precisely determined.

“We’ve refined our approach, and now we have higher accuracy and precision,” Bowring says. “You can think of it as slowly spiraling in toward the truth.”

Longmanshen fault zone still hazardous, suggest new reports

The 60-kilometer segment of the fault northeast of the 2013 Lushan rupture is the place in the region to watch for the next major earthquake, according to research published in Seismological Research Letters (SRL). Research papers published in this special section of SRL suggest the 2008 Wenchuan earthquake triggered the magnitude 6.6 Lushan quake.

Guest edited by Huajian Yao, professor of geophysics at the University of Science and Technology of China, the special section includes eight articles that present current data, description and preliminary analysis of the Lushan event and discuss the potential of future earthquakes in the region.

More than 87,000 people were killed or went missing as a result of the 2008 magnitude 7.9 Wenchuan earthquake in China’s Sichuan province, the largest quake to hit China since 1950. In 2013, the Lushan quake occurred ~90 km to the south and caused 203 deaths, injured 11,492 and affected more than 1.5 million people.

“After the 2008 magnitude 7.9 Wenchuan earthquake along the Longmenshan fault zone in western Sichuan of China, researchers in China and elsewhere have paid particular attention to this region, seeking to understand how the seismic hazard potential changed in the southern segment of the fault and nearby faults,” said Yao. “Yet the occurrence of this magnitude 6.6 Lushan event surprised many. The challenge of understanding where and when the next big quake will occur after a devastating seismic event continues after this Lushan event, although we now have gained much more information about this area.”

Preliminary rupture details

The southern part of the Longmenshan fault zone is complex and still only moderately understood. Similar to the central segment where the 2008 Wenchuan event occurred, the southern segment, which generated the Lushan rupture, includes the Wenchuan-Maoxian fault, Beichuan-Yingxiu fault, the Pengxian-Guanxian fault and Dayi faults, a series of sub-parallel secondary faults.

Although the Lushan earthquake’s mainshock did not break to the surface, the strong shaking still caused significant damage and casualties in the epicentral region. Three papers detail the rupture process of the Lushan quake. Libo Han from the China Earthquake Administration and colleagues provide a preliminary analysis of the Lushan mainshock and two large aftershocks, which appear to have occurred in the upper crust and terminated at a depth of approximately 8 km. While the Lushan earthquake cannot be associated with any identified surface faults, Han and colleagues suggest the quake may have occurred on a blind thrust fault subparallel to the Dayi fault, which lies at and partly defines the edge of the Chengdu basin. Based on observations from extensive trenching and mapping of fault activity after both the Wenchuan and Lushan earthquakes, Chen Lichun and colleagues from the China Earthquake Administration suggest the Lushan quake spread in a “piggyback fashion” toward the Sichuan basin, but with weaker activity and lower seismogenic potential than the Wenchuan quake. And Junju Xie, from the China Earthquake Administration and Beijing University of Technology, and colleagues examined the vertical and horizontal near-source strong motion from the Mw 6.8 Lushan earthquake. The vertical ground motion is relatively weak for this event, likely due to the fact that seismic energy dissipated at the depth of 12-25 km and the rupture did not break through the ground surface.

Possible link between Lushan and Wenchuan earthquakes

Were the Lushan and Wenchuan earthquakes related? And if so, what is the relationship? Some researchers consider the Lushan quake to be a strong aftershock of the Wenchuan quake, while others see them as independent events. In this special section, researchers tackled the question from various perspectives.

To discover whether the Lushan earthquake was truly independent from the Wenchuan quake, researchers need to have an accurate picture of where the Lushan quake originated. Yong Zhang from the GFZ German Research Centre for Geosciences and the China Earthquake Administration and colleagues begin this process by confirming a new hypocenter for Lushan. To find this place where the fault first began to rupture, the researchers analyze near-fault strong-motion data (movements that took place at a distance of up to a few tens of kilometers away from the fault) as well as long distance (thousands of kilometers ) teleseismic data.

Using their newly calculated location for the hypocenter, Zhang and colleagues now agree with earlier studies that suggest the initial Lushan rupture was a circular rupture event with no predominant direction. But they note that their calculations place the major slip area in the Lushan quake about 40 to 50 kilometers apart from the southwest end of the Wenchuan quake fault. This “gap” between the two faults may hold increased seismic hazards, caution Zhang and colleagues.

Ke Jia of Beijing University and colleagues explore the relationship of the two quakes with a statistical analysis of aftershocks in the region as well as the evolution of shear stress in the lower crust and upper mantle in the broader quake region. Their analyses suggest that the Wenchuan quake did affect the Lushan quake in an immediate sense by changing the overall background seismicity in the region. If these changes in background seismicity are taken into account, the researchers calculate a 62 percent probability that Lushan is a strong aftershock of Wenchuan.

Similarly, Yanzhao Wang from the China Earthquake Administration and colleagues quantified the stress loading of area faults due to the Wenchuan quake and suggest the change in stress may have caused the Lushan quake to rupture approximately 28.4 to 59.3 years earlier than expected. They conclude that the Lushan earthquake is at least 85 percent of a delayed aftershock of the Wenchuan earthquake, rather than due solely to long-term tectonic loading.

After the Wenchuan quake, researchers immediately began calculating stress changes on the major faults surrounding the rupture zone, in part to identify where dangerous aftershocks might occur and to test how well these stress change calculations might work to predict new earthquakes. As part of these analyses, Tom Parsons of the U.S. Geological Survey and Margarita Segou of GeoAzur compared data collected from the Wenchuan and Lushan quakes with data on aftershocks and stress change in four other major earthquakes, including the M 7.4 Landers and Izmit quakes in California and Turkey, respectively, and the M 7.9 Denali quake in Alaska and the M 7.1 Canterbury quake in New Zealand.

Their comparisons reveal that strong aftershocks similar to Lushan are likely to occur where there is highest overall aftershock activity, where stress change is the greatest and on well-developed fault zones. But they also note that by these criteria, the Lushan quake would only have been predicted by stress changes, and not the clustering of aftershocks following the 2008 Wenchuan event.

Future earthquakes in this region

After Wenchuan and Lushan, where should seismologists and other look for the next big quake in the region? After the 2008 Wenchuan quake, seismologists were primed with data to help predict where and when the next rupture might be in the region. The data suggested that the Wenchuan event would increase seismic stress in the southern Longmenshan fault that was the site of the 2013 Lushan quake. But that information alone could not predict that the southern Longmenshan fault would be the next to rupture after Wenchuan, say Mian Liu of the University of Missouri and colleagues, because the Wenchuan earthquake also increased the stress on numerous others faults in the region

Additional insights can be gained from seismic moment studies, according to Liu and colleagues. Moment balancing compares how much seismic strain energy is accumulated along a fault over a certain period with the amount of strain energy released over the same period. In the case of the Longmenshan fault, there had been a slow accumulation of strain energy without release by a major seismic event for more than a millennium. After the Wenchuan quake, the southern part of the Longmenshan fault became the fault with the greatest potential for a quake. And now, after Lushan, Liu and colleagues say that the 60 kilometer-long segment of the fault northeast of the Lushan rupture is the place in the region to watch for the next major earthquake.

Rising mountains dried out Central Asia, scientists say

A record of ancient rainfall teased from long-buried sediments in Mongolia is challenging the popular idea that the arid conditions prevalent in Central Asia today were caused by the ancient uplift of the Himalayas and the Tibetan Plateau.

Instead, Stanford scientists say the formation of two lesser mountain ranges, the Hangay and the Altai, may have been the dominant drivers of climate in the region, leading to the expansion of Asia’s largest desert, the Gobi. The findings will be presented on Thursday, Dec. 12, at the annual meeting of the American Geophysical Union (AGU) in San Francisco.

“These results have major implications for understanding the dominant factors behind modern-day Central Asia’s extremely arid climate and the role of mountain ranges in altering regional climate,” said Page Chamberlain, a professor of environmental Earth system science at Stanford.

Scientists previously thought that the formation of the Himalayan mountain range and the Tibetan plateau around 45 million years ago shaped Asia’s driest environments.

“The traditional explanation has been that the uplift of the Himalayas blocked air from the Indian Ocean from reaching central Asia,” said Jeremy Caves, a doctoral student in Chamberlain’s terrestrial paleoclimate research group who was involved in the study.

This process was thought to have created a distinct rain shadow that led to wetter climates in India and Nepal and drier climates in Central Asia. Similarly, the elevation of the Tibetan Plateau was thought to have triggered an atmospheric process called subsidence, in which a mass of air heated by a high elevation slowly sinks into Central Asia.

“The falling air suppresses convective systems such as thunderstorms, and the result is you get really dry environments,” Caves said.

This long-accepted model of how Central Asia’s arid environments were created mostly ignores, however, the existence of the Altai and Hangay, two northern mountain ranges.

Searching for answers


To investigate the effects of the smaller ranges on the regional climate, Caves and his colleagues from Stanford and Rocky Mountain College in Montana traveled to Mongolia in 2011 and 2012 and collected samples of ancient soil, as well as stream and lake sediments from remote sites in the central, southwestern and western parts of the country.

The team carefully chose its sites by scouring the scientific literature for studies of the region conducted by pioneering researchers in past decades.

“A lot of the papers were by Polish and Russian scientists who went there to look for dinosaur fossils,” said Hari Mix, a doctoral student at Stanford who also participated in the research. “Indeed, at many of the sites we visited, there were dinosaur fossils just lying around.”

The earlier researchers recorded the ages and locations of the rocks they excavated as part of their own investigations; Caves and his team used those age estimates to select the most promising sites for their own study.

At each site, the team bagged sediment samples that were later analyzed to determine their carbon isotope content. The relative level of carbon isotopes present in a soil sample is related to the productivity of plants growing in the soil, which is itself dependent on the annual rainfall. Thus, by measuring carbon isotope amounts from different sediment samples of different ages, the team was able to reconstruct past precipitation levels.

An ancient wet period


The new data suggest that rainfall in central and southwestern Mongolia had decreased by 50 to 90 percent in the last several tens of million of years.

“Right now, precipitation in Mongolia is about 5 inches annually,” Caves said. “To explain our data, rainfall had to decrease from 10 inches a year or more to its current value over the last 10 to 30 million years.”

That means that much of Mongolia and Central Asia were still relatively wet even after the formation of the Himalayas and the Tibetan Plateau 45 million years ago. The data show that it wasn’t until about 30 million years ago, when the Hangay Mountains first formed, that rainfall started to decrease. The region began drying out even faster about 5 million to 10 million years ago, when the Altai Mountains began to rise.

The scientists hypothesize that once they formed, the Hangay and Altai ranges created rain shadows of their own that blocked moisture from entering Central Asia.

“As a result, the northern and western sides of these ranges are wet, while the southern and eastern sides are dry,” Caves said.

The team is not discounting the effect of the Himalayas and the Tibetan Plateau entirely, because portions of the Gobi Desert likely already existed before the Hangay or Altai began forming.

“What these smaller mountains did was expand the Gobi north and west into Mongolia,” Caves said.

The uplift of the Hangay and Altai may have had other, more far-reaching implications as well, Caves said. For example, westerly winds in Asia slam up against the Altai today, creating strong cyclonic winds in the process. Under the right conditions, the cyclones pick up large amounts of dust as they snake across the Gobi Desert. That dust can be lofted across the Pacific Ocean and even reach California, where it serves as microscopic seeds for developing raindrops.

The origins of these cyclonic winds, as well as substantial dust storms in China today, may correlate with uplift of the Altai, Caves said. His team plans to return to Mongolia and Kazakhstan next summer to collect more samples and to use climate models to test whether the Altai are responsible for the start of the large dust storms.

“If the Altai are a key part of regulating Central Asia’s climate, we can go and look for evidence of it in the past,” Caves said.