Past temperature in Greenland adjusted

The revised Greenland temperature history (black curve, grey uncertainties) for the period 18,000 to 10,000 before present. This temperature history is based on temperature interpretation from nitrogen measurements (green curve) and O18 diffusion measurements (red curve). The blue curve is from a previous study, based on nitrogen measurements. -  Niels Bohr Institute
The revised Greenland temperature history (black curve, grey uncertainties) for the period 18,000 to 10,000 before present. This temperature history is based on temperature interpretation from nitrogen measurements (green curve) and O18 diffusion measurements (red curve). The blue curve is from a previous study, based on nitrogen measurements. – Niels Bohr Institute

One of the common perceptions about the climate is that the amount of carbon dioxide in the atmosphere, solar radiation and temperature follow each other – the more solar radiation and the more carbon dioxide, the hotter the temperature. This correlation is also seen in the Greenland ice cores that are drilled through the approximately three kilometer thick ice sheet. But during a period of several thousand years up until the last ice age ended approximately 12,000 years ago, this pattern did not fit and this was a mystery to researchers. Now researchers from the Niels Bohr Institute have solved this mystery using new analytical techniques. The results are published in the prestigious scientific journal Science.

The Greenland ice sheet is an archive of knowledge about the Earth’s climate more than 125,000 years back in time. The ice was formed by the precipitation that fell as snow from the clouds and remained year after year, gradually being compressed into ice. By drilling down through the approximately three kilometer thick ice sheet, the researchers draw up ice cores, which provide detailed knowledge of the climate of the past annual layer after annual layer. By measuring the content of the special oxygen isotope O18 in the ice cores, you can get information about the temperature in the past climate, year by year.

But something didn’t fit. In Greenland, the end of the Ice Age started 15,000 years ago and the temperature rose quickly. Then it became colder again until 12,000 years ago, when there was again a rapid rise in temperature. The first rise in temperature is called the Bølling-Allerød interstadial and the second is called the Holocene interglacial.

Temperatures contrary to expectations

“We could see that the concentration of carbon dioxide and solar radiation was higher during the cold period between the two warm periods compared with the cold period before the first warming 15,000 years ago. But the temperature measurements based on the oxygen isotope O18 showed that the period between the two warm periods was colder than the cold period before the first warming 15,000 years ago. This was the exact opposite of what you would expect,” explains postdoc Vasileios Gkinis, Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen.

The researchers investigated ice cores from three different Greenland ice cores: the NEEM project, the NGRIP project and the GISP 2 project. But amount of the oxygen isotope O18 was not enough to reconstruct period temperatures in detail or their geographic distribution.

To get more detailed temperature data, the researchers used two relatively new methods of investigation, both of which examine the layer of compressed granular snow that is formed between the top layer of soft and fluffy snow and the layer deeper down in the ice sheet, where the compressed snow has been turned into ice. This process of transforming the fluffy snow into hard ice is physical and both the thickness and the movement of the water molecules are dependent on the temperature.

“With the first method, we measured the nitrogen content and by measuring the relationship between the two isotopes of nitrogen, N15 and N14, we could reconstruct the thickness of the compressed snow 19,000 years back in time,” explains Vasileios Gkinis.

The second method involved measuring the spread of air with water molecules with different isotope composition in the layers with the compressed snow. This process of smoothing the original water isotope variations from precipitation is dependent on the temperature, as the water molecules in vapour form are more mobile at warmer temperatures.

Temperatures ‘fall into place’

Data for the spread of the water molecules in the individual annual layers in the Greenland ice cores has thus made it possible to calculate the temperature in the layers with compressed snow 19,000 years back in time.

“What we discovered was that the previous temperature curve, which was only based on the measurements of the oxygen isotope O18, was inaccurate. The oxygen temperature curve said that the climate in central Greenland was colder around 12,000 years ago than around 15,000 years ago, despite the fact that two key climate drivers – carbon dioxide in the atmosphere and solar radiation – would suggest the opposite. With our new, more direct reconstruction, we have been able to show that the climate in central Greenland was actually warmer around 12,000 years ago compared to 15,000 years ago. So the temperatures actually follow the solar radiation and the amount of carbon dioxide in the atmosphere. We estimate that the temperature difference was 2-6 degrees,” says Bo Vinther, Associate Professor at the Centre for Ice and Climate at the Niels Bohr Institute, University of Copenhagen.

Trinity geologists re-write Earth’s evolutionary history books

The study site landscape is shown with boulders of the paleosol in the foreground. -  Quentin Crowley
The study site landscape is shown with boulders of the paleosol in the foreground. – Quentin Crowley

Geologists from Trinity College Dublin have rewritten the evolutionary history books by finding that oxygen-producing life forms were present on Earth some 3 billion years ago – a full 60 million years earlier than previously thought. These life forms were responsible for adding oxygen (O2) to our atmosphere, which laid the foundations for more complex life to evolve and proliferate.

Working with Professors Joydip Mukhopadhyay and Gautam Ghosh and other colleagues from the Presidency University in Kolkata, India, the geologists found evidence for chemical weathering of rocks leading to soil formation that occurred in the presence of O2. Using the naturally occurring uranium-lead isotope decay system, which is used for age determinations on geological time-scales, the authors deduced that these events took place at least 3.02 billion years ago. The ancient soil (or paleosol) came from the Singhbhum Craton of Odisha, and was named the ‘Keonjhar Paleosol’ after the nearest local town.

The pattern of chemical weathering preserved in the paleosol is compatible with elevated atmospheric O2 levels at that time. Such substantial levels of oxygen could only have been produced by organisms converting light energy and carbon dioxide to O2 and water. This process, known as photosynthesis, is used by millions of different plant and bacteria species today. It was the proliferation of such oxygen-producing species throughout Earth’s evolutionary trajectory that changed the composition of our atmosphere – adding much more O2 – which was as important for the development of ancient multi-cellular life as it is for us today.

Quentin Crowley, Ussher Assistant Professor in Isotope Analysis and the Environment in the School of Natural Sciences at Trinity, is senior author of the journal article that describes this research which has just been published online in the world’s top-ranked Geology journal, Geology. He said: “This is a very exciting finding, which helps to fill a gap in our knowledge about the evolution of the early Earth. This paleosol from India is telling us that there was a short-lived pulse of atmospheric oxygenation and this occurred considerably earlier than previously envisaged.”

The early Earth was very different to what we see today. Our planet’s early atmosphere was rich in methane and carbon dioxide and had only very low levels of O2. The widely accepted model for evolution of the atmosphere states that O2 levels did not appreciably rise until about 2.4 billion years ago. This ‘Great Oxidation Event’ event enriched the atmosphere and oceans with O2, and heralded one of the biggest shifts in evolutionary history.

Micro-organisms were certainly present before 3.0 billion years ago but they were not likely capable of producing O2 by photosynthesis. Up until very recently however, it has been unclear if any oxygenation events occurred prior to the Great Oxidation Event and the argument for an evolutionary capability of photosynthesis has largely been based on the first signs of an oxygen build-up in the atmosphere and oceans.

“It is the rare examples from the rock record that provide glimpses of how rocks weathered,” added Professor Crowley. “The chemical changes which occur during this weathering tell us something about the composition of the atmosphere at that time. Very few of these ‘paleosols’ have been documented from a period of Earth’s history prior to 2.5 billion years ago. The one we worked on is at least 3.02 billion years old, and it shows chemical evidence that weathering took place in an atmosphere with elevated O2 levels.”

There was virtually no atmospheric O2 present 3.4 billion years ago, but recent work from South African paleosols suggested that by about 2.96 billion years ago O2 levels may have begun to increase. Professor Crowley’s finding therefore moves the goalposts back at least 60 million years, which, given humans have only been on the planet for around a tenth of that time, is not an insignificant drop in the evolutionary ocean.

Professor Crowley concluded: “Our research gives further credence to the notion of early and short-lived atmospheric oxygenation.

This particular example is the oldest known example of oxidative weathering from a terrestrial environment, occurring about 600 million years before the Great Oxidation Event that laid the foundations for the evolution of complex life.”

Ancient shellfish remains rewrite 10,000-year history of El Nino cycles

The middens are ancient dumping sites that typically contain a mix of mollusk shells, fish and bird bones, ceramics, cloth, charcoal, maize and other plants. -  M. Carré / Univ. of Montpellier
The middens are ancient dumping sites that typically contain a mix of mollusk shells, fish and bird bones, ceramics, cloth, charcoal, maize and other plants. – M. Carré / Univ. of Montpellier

The planet’s largest and most powerful driver of climate changes from one year to the next, the El Niño Southern Oscillation in the tropical Pacific Ocean, was widely thought to have been weaker in ancient times because of a different configuration of the Earth’s orbit. But scientists analyzing 25-foot piles of ancient shells have found that the El Niños 10,000 years ago were as strong and frequent as the ones we experience today.

The results, from the University of Washington and University of Montpellier, question how well computer models can reproduce historical El Niño cycles, or predict how they could change under future climates. The paper is now online and will appear in an upcoming issue of Science.

“We thought we understood what influences the El Niño mode of climate variation, and we’ve been able to show that we actually don’t understand it very well,” said Julian Sachs, a UW professor of oceanography.

The ancient shellfish feasts also upend a widely held interpretation of past climate.

“Our data contradicts the hypothesis that El Niño activity was very reduced 10,000 years ago, and then slowly increased since then,” said first author Matthieu Carré, who did the research as a UW postdoctoral researcher and now holds a faculty position at the University of Montpellier in France.

In 2007, while at the UW-based Joint Institute for the Study of the Atmosphere and Ocean, Carré accompanied archaeologists to seven sites in coastal Peru. Together they sampled 25-foot-tall piles of shells from Mesodesma donacium clams eaten and then discarded over centuries into piles that archaeologists call middens.

While in graduate school, Carré had developed a technique to analyze shell layers to get ocean temperatures, using carbon dating of charcoal from fires to get the year, and the ratio of oxygen isotopes in the growth layers to get the water temperatures as the shell was forming.

The shells provide 1- to 3-year-long records of monthly temperature of the Pacific Ocean along the coast of Peru. Combining layers of shells from each site gives water temperatures for intervals spanning 100 to 1,000 years during the past 10,000 years.

The new record shows that 10,000 years ago the El Niño cycles were strong, contradicting the current leading interpretations. Roughly 7,000 years ago the shells show a shift to the central Pacific of the most severe El Niño impacts, followed by a lull in the strength and occurrence of El Niño from about 6,000 to 4,000 years ago.

One possible explanation for the surprising finding of a strong El Niño 10,000 years ago was that some other factor was compensating for the dampening effect expected from cyclical changes in Earth’s orbit around the sun during that period.

“The best candidate is the polar ice sheet, which was melting very fast in this period and may have increased El Niño activity by changing ocean currents,” Carré said.

Around 6,000 years ago most of the ice age floes would have finished melting, so the effect of Earth’s orbital geometry might have taken over then to cause the period of weak El Niños.

In previous studies, warm-water shells and evidence of flooding in Andean lakes had been interpreted as signs of a much weaker El Niño around 10,000 years ago.

The new data is more reliable, Carré said, for three reasons: the Peruvian coast is strongly affected by El Niño; the shells record ocean temperature, which is the most important parameter for the El Niño cycles; and the ability to record seasonal changes, the timescale at which El Niño can be observed.

“Climate models and a variety of datasets had concluded that El Niños were essentially nonexistent, did not occur, before 6,000 to 8,000 years ago,” Sachs said. “Our results very clearly show that this is not the case, and suggest that current understanding of the El Niño system is incomplete.

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.

Antarctic ice sheet is result of CO2 decrease, not continental breakup

Climate modelers from the University of New Hampshire have shown that the most likely explanation for the initiation of Antarctic glaciation during a major climate shift 34 million years ago was decreased carbon dioxide (CO2) levels. The finding counters a 40-year-old theory suggesting massive rearrangements of Earth’s continents caused global cooling and the abrupt formation of the Antarctic ice sheet. It will provide scientists insight into the climate change implications of current rising global CO2 levels.

In a paper published today in Nature, Matthew Huber of the UNH Institute for the Study of Earth, Oceans, and Space and department of Earth sciences provides evidence that the long-held, prevailing theory known as “Southern Ocean gateway opening” is not the best explanation for the climate shift that occurred during the Eocene-Oligocene transition when Earth’s polar regions were ice-free.

“The Eocene-Oligocene transition was a major event in the history of the planet and our results really flip the whole story on its head,” says Huber. “The textbook version has been that gateway opening, in which Australia pulled away from Antarctica, isolated the polar continent from warm tropical currents, and changed temperature gradients and circulation patterns in the ocean around Antarctica, which in turn began to generate the ice sheet. We’ve shown that, instead, CO2-driven cooling initiated the ice sheet and that this altered ocean circulation.”

Huber adds that the gateway theory has been supported by a specific, unique piece of evidence-a “fingerprint” gleaned from oxygen isotope records derived from deep-sea sediments. These sedimentary records have been used to map out gradient changes associated with ocean circulation shifts that were thought to bear the imprint of changes in ocean gateways.

Although declining atmospheric levels of CO2 has been the other main hypothesis used to explain the Eocene-Oligocene transition, previous modeling efforts were unsuccessful at bearing this out because the CO2 drawdown does not by itself match the isotopic fingerprint. It occurred to Huber’s team that the fingerprint might not be so unique and that it might also have been caused indirectly from CO2 drawdown through feedbacks between the growing Antarctic ice sheet and the ocean.

Says Huber, “One of the things we were always missing with our CO2 studies, and it had been missing in everybody’s work, is if conditions are such to make an ice sheet form, perhaps the ice sheet itself is affecting ocean currents and the climate system-that once you start getting an ice sheet to form, maybe it becomes a really active part of the climate system and not just a passive player.”

For their study, Huber and colleagues used brute force to generate results: they simply modeled the Eocene-Oligocene world as if it contained an Antarctic ice sheet of near-modern size and shape and explored the results within the same kind of coupled ocean-atmosphere model used to project future climate change and across a range of CO2 values that are likely to occur in the next 100 years (560 to 1200 parts per million).

“It should be clear that resolving these two very different conceptual models for what caused this huge transformation of the Earth’s surface is really important because today as a global society we are, as I refer to it, dialing up the big red knob of carbon dioxide but we’re not moving continents around.”

Just what caused the sharp drawdown of CO2 is unknown, but Huber points out that having now resolved whether gateway opening or CO2 decline initiated glaciation, more pointed scientific inquiry can be focused on answering that question.

Huber notes that despite his team’s finding, the gateway opening theory won’t now be shelved, for that massive continental reorganization may have contributed to the CO2 drawdown by changing ocean circulation patterns that created huge upwellings of nutrient-rich waters containing plankton that, upon dying and sinking, took vast loads of carbon with them to the bottom of the sea.

Studies show movements of continents speeding up after slow ‘middle age’

Two studies show that the movement rate of plates carrying the Earth’s crust may not be constant over time. This could provide a new explanation for the patterns observed in the speed of evolution and has implications for the interpretation of climate models. The work is presented today at Goldschmidt 2014, the premier geochemistry conference taking place in Sacramento, California, USA.

The Earth’s continental crust can be thought of as an archive of Earth’s history, containing information on rock formation, the atmosphere and the fossil record. However, it is not clear when and how regularly crust formed since the beginning of Earth history, 4.5 billion years ago.

Researchers led by Professor Peter Cawood, from the University of St. Andrews, UK, examined several measures of continental movement and geologic processes from a number of previous studies. They found that, from 1.7 to 0.75 billion years ago (termed Earth’s middle age), Earth appears to have been very stable in terms of its environment, with little in the way of crust building activity, no major fluctuations in atmospheric composition and few major developments seen in the fossil record. This contrasts markedly with the time periods either side of this, which contained major ice ages and changes in oxygen levels. Earth’s middle age also coincides with the formation of a supercontinent called Rodinia, which appears to have been stable throughout this time.

Professor Cawood suggests this stability may have been due to the gradual cooling of the earth’s crust over time. “Before 1.7 billion years ago, the Earth’s crust would have been substantially hotter, meaning that continental plate movement may have been governed by different rules to those that operate today,” said Professor Cawood. “0.75 billion years ago, the crust reached a point where it had cooled sufficiently to allow modern day plate tectonics to start working, in particular allowing subduction zones to form (where one plate of the crust moves under another). This increase in activity could have kick-started a myriad of changes including the break-up of Rodinia and changes to levels of key elements in the atmosphere and seas, which in turn may have induced evolutionary changes in the life forms present.”

This view is backed up by work from Professor Kent Condie from New Mexico Tech, USA, which suggests the movement rate of the Earth’s crust is not constant but may be speeding up over time. Professor Condie examined how supercontinents assemble and break up. “Our results challenge the view that the rate of plate movement is stable over time,” said Professor Condie. “The interpretation of data from many other disciplines such as stable isotope geochemistry, palaeontology and paleoclimatology in part rely on the assumption that the movement rate of the Earth’s crust is constant.”

Results from these fields may now need to be re-examined in light of Condie’s findings. “We now urgently need to collect further data on critical time periods to understand more about the constraints on plate speeds and the frequency of collision between continental blocks,” concluded Professor Condie.

Geologists confirm oxygen levels of ancient oceans

Assistant Professor Zunli Lu co-authored the study. -  Syracuse University News Services
Assistant Professor Zunli Lu co-authored the study. – Syracuse University News Services

Geologists in the College of Arts and Sciences have discovered a new way to study oxygen levels in the Earth’s oldest oceans.

Zunli Lu and Xiaoli Zhou, an assistant professor and Ph.D. student, respectively, in the Department of Earth Sciences, are part of an international team of researchers whose findings have been published by the journal Geology (Geological Society of America, 2014). Their research approach may have important implications for the study of marine ecology and global warming.

“More than 2.5 billion years ago, there was little to no oxygen in the oceans, as methane shrouded the Earth in a haze,” says Lu, a member of Syracuse University’s Low-Temperature Geochemistry Research Group. “Organisms practicing photosynthesis eventually started to overpower reducing chemical compounds [i.e., electron donors], and oxygen began building up in the atmosphere. This period has been called the Great Oxidation Event.”

Using a novel approach called iodine geochemistry, Lu, Zhou and their colleagues have confirmed the earliest appearance of dissolved oxygen in the ocean’s surface waters.

Central to their approach is iodate, a form of iodine that exists only in oxygenated waters. When iodate is detected in carbonate rocks in a marine setting, Lu and company are able to measure the elemental ratio of iodine to calcium. This measurement, known as a proxy for ocean chemistry, helps them figure out how much oxygen has dissolved in the water.

“Iodine geochemistry enables us to constrain oxygen levels in oceans that have produced calcium carbonate minerals and fossils,” says Lu, who developed the proxy. “What we’ve found in ancient rock reinforces the proxy’s reliability. Already, we’re using the proxy to better understand the consequences of ocean deoxygenation, due to rapid global warming.”

New isotopic evidence supporting moon formation via Earth collision with planet-sized body

A new series of measurements of oxygen isotopes provides increasing evidence that the Moon formed from the collision of the Earth with another large, planet-sized astronomical body, around 4.5 billion years ago. This work will be published in Science* on 6th June, and will be presented to the Goldschmidt geochemistry conference in California on 11th June.

Most planetary scientists believe that the Moon formed from an impact between the Earth and a planet-sized body, which has been given the name Theia. Efforts to confirm that the impact had taken place had centred on measuring the ratios between the isotopes of oxygen, titanium, silicon and others. These ratios are known to vary throughout the solar system, but their close similarity between Earth and Moon conflicted with theoretical models of the collision that indicated that the Moon would form mostly from Theia, and thus would be expected to be compositionally different from the Earth.

Now a group of German researchers, led by Dr. Daniel Herwartz, have used more refined techniques to compare the ratios of 17O/16O in lunar samples, with those from Earth. The team initially used lunar samples which had arrived on Earth via meteorites, but as these samples had exchanged their isotopes with water from Earth, fresher samples were sought. These were provided by NASA from the Apollo 11, 12 and 16 missions; they were found to contain significantly higher levels of 17O/16O than their Earthly counterparts.

Dr Herwartz said
“The differences are small and difficult to detect, but they are there. This means two things; firstly we can now be reasonably sure that the Giant collision took place. Secondly, it gives us an idea of the geochemistry of Theia. Theia seems to have been similar to what we call E-type chondrites**.If this is true, we can now predict the geochemical and isotopic composition of the Moon, because the present Moon is a mixture of Theia and the early Earth. The next goal is to find out how much material of Theia is in the Moon”.

Most models estimate that the Moon it is composed of around 70% to 90% material from Theia, with the remaining 10% to 30% coming from the early Earth. However, some models argue for as little as 8% Theia in the Moon. Dr Herwartz said that the new data indicate that a 50:50 mixture seems possible, but this needs to be confirmed.

The team used an advanced sample preparation technique before measuring the samples via stable isotope ratio mass spectrometry, which showed a 12 parts per million (± 3 ppm) difference in 17O/16O ratio between Earth and Moon.

Australia’s deadly eruptions the reason for the first mass extinction

A Curtin University researcher has shown that ancient volcanic eruptions in Australia 510 million years ago significantly affected the climate, causing the first known mass extinction in the history of complex life.

Published in prestigious journal Geology, Curtin’s Associate Professor Fred Jourdan, along with colleagues from several Australian and international institutions, used radioactive dating techniques to precisely measure the age of the eruptions of the Kalkarindji volcanic province.

Dr Jourdan and his team were able to prove the volcanic province occurred at the same time as the Early-Middle Cambrian extinction from 510-511 million years ago – the first extinction to wipe out complex multicellular life.

“It has been well-documented that this extinction, which eradicated 50 per cent of species, was related to climatic changes and depletion of oxygen in the oceans, but the exact mechanism causing these changes was not known, until now,” Dr Jourdan said.

“Not only were we able to demonstrate that the Kalkarindji volcanic province was emplaced at the exact same time as the Cambrian extinction, but were also able to measure a depletion of sulphur dioxide from the province’s volcanic rocks – which indicates sulphur was released into the atmosphere during the eruptions.

“As a modern comparison, when the small volcano Pinatubo erupted in 1991, the resulting discharge of sulphur dioxide decreased the average global temperatures by a few tenths of a degree for a few years following the eruption.

“If relatively small eruptions like Pinatubo can affect the climate just imagine what a volcanic province with an area equivalent to the size of the state of Western Australia can do.”

The team then compared the Kalkarindji volcanic province with other volcanic provinces and showed the most likely process for all the mass extinctions was a rapid oscillation of the climate triggered by volcanic eruptions emitting sulphur dioxide, along with greenhouse gases methane and carbon dioxide.

“We calculated a near perfect chronological correlation between large volcanic province eruptions, climate shifts and mass extinctions over the history of life during the last 550 million years, with only one chance over 20 billion that this correlation is just a coincidence,” Dr Jourdan said.

Dr Jourdan said the rapid oscillations of the climate produced by volcanic eruptions made it difficult for various species to adapt, ultimately resulting in their demise. He also stressed the importance of this research to better understand our current environment.

“To comprehend the long-term climatic and biological effects of the massive injections of gas in the atmosphere by modern society, we need to recognise how climate, oceans and ecosytems were affected in the past,” he said.

Taking the pulse of mountain formation in the Andes

Sedimentary deposits near Cerdas in the Altiplano plateau of Bolivia are shown. These rocks contain ancient soils used to decipher the surface temperature and surface uplift history of the southern Altiplano. -  Photo by Carmala Garzione/University of Rochester.
Sedimentary deposits near Cerdas in the Altiplano plateau of Bolivia are shown. These rocks contain ancient soils used to decipher the surface temperature and surface uplift history of the southern Altiplano. – Photo by Carmala Garzione/University of Rochester.

Scientists have long been trying to understand how the Andes and other broad, high-elevation mountain ranges were formed. New research by Carmala Garzione, a professor of earth and environmental sciences at the University of Rochester, and colleagues sheds light on the mystery.

In a paper published in the latest Earth and Planetary Science Letters, Garzione explains that the Altiplano plateau in the central Andes-and most likely the entire mountain range-was formed through a series of rapid growth spurts.

“This study provides increasing evidence that the plateau formed through periodic rapid pulses, not through a continuous, gradual uplift of the surface, as was traditionally thought,” said Garzione. “In geologic terms, rapid means rising one kilometer or more over several millions of years, which is very impressive.”

It’s been understood that the Andes mountain range has been growing as the Nazca oceanic plate slips underneath the South American continental plate, causing the Earth’s crust to shorten (by folding and faulting) and thicken. But that left two questions: How quickly have the Andes risen to their current height, and what was the actual process that enabled their rise?

Several years ago (2006-2008), Garzione and several colleagues provided the first estimates of the timing and rates of the surface uplift of the central Andes (“Mountain Ranges Rise Much More Rapidly than Geologists Expected”) by measuring the ancient surface temperatures and rainfall compositions preserved in the soils of the central Altiplano, a plateau in Bolivia and Peru that sits about 12,000 feet above sea level. Garzione concluded that portions of the dense lower crust and upper mantle that act like an anchor on the base of the crust are periodically detached and sink through the mantle as the thickened continental plate heats up. Detachment of this dense anchor allows the Earth’s low density upper crust to rebound and rise rapidly.

More recently, Garzione and Andrew Leier, an assistant professor of Earth and Ocean Sciences at the University of South Carolina, used a relatively new temperature-recording technique in two separate studies in different regions of the Andes to determine whether pulses of rapid surface uplift are the norm, or the exception, for the formation of mountain ranges like the Andes.

Garzione and Leier (“Stable isotope evidence for multiple pulses of rapid surface uplift in the Central Andes, Bolivia”) both focused on the bonding behavior of carbon and oxygen isotopes in the mineral calcite that precipitated from rainwater; their results were similar.

Garzione worked in the southern Altiplano, collecting climate records preserved in ancient soils at both low elevations (close to sea level), where temperatures remained warm over the history of the Andes, and at high elevations where temperatures should have cooled as the mountains rose. The calcite found in the soil contains both the lighter isotopes of carbon and oxygen-12C and 16O-as well as the rare heavier isotopes-13C and 18O. Paleo-temperature estimates from calcite rely on the fact that heavy isotopes form stronger bonds. At lower temperatures, where atoms vibrate more slowly, the heavy isotope 13C-18O bonds would be more difficult to break, resulting in a higher concentration of 13C-18O bonds in calcite, compared to what is found at warmer temperatures. By measuring the abundance of heavy isotope bonds in both low elevation (warm) sites and high elevation (cooler) sites over time, Garzione used the temperature difference between the sites to estimate the elevation of various layers of ancient soils at specific points in time.

She found that the southern Altiplano region rose by about 2.5 kilometers between 16 million and 9 million years ago, which is considered a rapid rate in geologic terms. Garzione speculates that the pulsing action relates to a dense root that grows at the boundary of the lower crust and upper mantle. As the oceanic plate slips under the continental plate, the continental plate shortens and thickens, increasing the pressure on the lower crust. The basaltic composition of the lower crust converts to a very high-density rock called eclogite, which serves as an anchor to the low-density upper crust. As this root is forced deeper into the hotter part of the mantle, it heats to a temperature where it can be rapidly removed (over several million years), resulting in the rapid rise of the mountain range.

“What we are learning is that the Altiplano plateau formed by pulses of rapid surface uplift over several million years, separated by long periods (several tens of million years) of stable elevations,” said Garzione. “We suspect this process is typical of other high-elevation ranges, but more research is needed before we know for certain.”