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Our future on Earth may also be our past. In a study published in the Proceedings of the National Academy of Sciences, researchers show that humans are reversing a long-term cooling trend tracing back at least 50 million years. And it's taken just two centuries.

Epihippus gracilis, one of the many early horses found in the Hancock Mammal Quarry in Oregon, depicted around 30 million years ago. Their ancestors would have gotten their start in the Eocene [Credit: National Park Services]

By 2030, Earth's climate is expected to resemble that of the mid-Pliocene, going back more than 3 million years in geologic time. Without reductions in our greenhouse gas emissions, our climates by 2150 could compare to the warm and mostly ice-free Eocene, an epoch that characterized the globe 50 million years ago.

"If we think about the future in terms of the past, where we are going is uncharted territory for human society," says the study's lead author, Kevin Burke, who conducted the work while a graduate student in the lab of paleoecologist John "Jack" Williams, professor of geography at the University of Wisconsin-Madison. "We are moving toward very dramatic changes over an extremely rapid time frame, reversing a planetary cooling trend in a matter of centuries."

All of the species on Earth today had an ancestor that survived the Eocene and the Pliocene, but whether humans and the flora and fauna we are familiar with can adapt to these rapid changes remains to be seen. The accelerated rate of change appears to be faster than anything life on the planet has experienced before.

The new study builds upon work Williams and colleagues first published in 2007, which compared future climate projections to historical climate data from the early 20th century. The new study relies on extensive data about climate conditions to probe much deeper in Earth's geologic past and expand those comparisons.

"We can use the past as a yardstick to understand the future, which is so different from anything we have experienced in our lifetimes," says Williams. "People have a hard time projecting what the world will be like five or 10 years from now. This is a tool for predicting that -- how we head down those paths, and using deep geologic analogs from Earth's history to think about changes in time."

During the Eocene, Earth's continents were packed more closely together and global temperatures averaged 23.4 degrees Fahrenheit (13 degrees Celsius) warmer than they are today. Dinosaurs had recently gone extinct and the first mammals, like ancestral whales and horses, were spreading across the globe. The Arctic was occupied by swampy forests like those found today in the southern U.S.

Future climate analogs for the years 2020, 2050, 2100 and 2200 according to three well-established models. If greenhouse gas emissions are not curbed, the study says, the climate will continue to warm until it begins to resemble the Eocene in 2100 [Credit: Burke et al. 2018]

In the Pliocene, North and South America joined tectonically, the climate was arid, land bridges allowed animals to spread across continents and the Himalayas formed. Temperatures were between 3.2 and 6.5 degrees Fahrenheit (1.8 to 3.6 degrees Celsius) warmer than they are today.

For the study, Burke and Williams -- along with colleagues at the University of Bristol, Columbia University, University of Leeds, NASA Goddard Institute for Space Studies and the National Center for Atmospheric Research -- examined the similarities between future climate projections as set forth by the Intergovernmental Panel on Climate Change Fifth Assessment Report and several periods of geologic history.

These included the Early Eocene, the mid-Pliocene, the Last Interglacial (129 to 116 thousand years ago), the mid-Holocene (6,000 years ago), the pre-industrial era (before A.D. 1850) and the early 20th century.

They used Representative Concentration Pathway 8.5 (RCP8.5), which represents a future climate scenario in which we do not mitigate greenhouse gas emissions, and RCP4.5, a scenario in which we moderately reduce greenhouse gas emissions, and climate simulations using three different but well-established models: the Hadley Centre Coupled Model version 3, the Goddard Institute for Space Studies ModelE2-R and the Community Climate System Model.

While not without their flaws, each of these models represents the best available data and state-of-the-art techniques.

Under both scenarios and across each model, compared to previous eras, the Earth's climate most closely resembled the mid-Pliocene by 2030 (under RCP8.5) or 2040 (under RCP4.5). Under the greenhouse gas stabilization scenario of RCP4.5, the climate then stabilizes at mid-Pliocene-like conditions, but under the higher greenhouse gas emissions of RCP8.5, the climate continues to warm until it begins to resemble the Eocene in 2100, achieving Eocene-like conditions more broadly by 2150.

The models showed these deep-geological climates emerging first from the center of continents and then expanding outward over time. Temperatures rise, precipitation increases, ice caps melt and climates become temperate near the Earth's poles.

"Madison (Wisconsin) warms up more than Seattle (Washington) does, even though they're at the same latitude," Williams explains. "When you read that the world is expected to warm by 3 degrees Celsius this century, in Madison we should expect to roughly double the global average."


The study also showed that under RCP8.5, "novel" climates emerge across nearly 9 percent of the planet. These are conditions that do not have known geologic or historical precedent and they concentrate in eastern and southeastern Asia, northern Australia and the coastal Americas.

"Based on observational data, we are tracking on the high end of the emissions scenarios, but it's too soon to tell," says Burke. "We may be somewhere between RCP4.5 and RCP8.5, though if we increase our climate mitigation efforts -- like switching to renewable energy -- we could find ourselves closer to the low end."

About a decade ago, Swedish scientist Johan Rockström and colleagues introduced the idea of "safe operating space," referring to the climate conditions under which modern agricultural societies developed. By comparing to the deep past, Williams and Burke say, we are able to better understand the planetary boundaries and thresholds that delineate this space.

"The further we move from the Holocene, the greater the potential that we move out of safe operating space," says Williams, a faculty affiliate with the UW-Madison Nelson Institute Center for Climatic Research. "In the roughly 20 to 25 years I have been working in the field, we have gone from expecting climate change to happen, to detecting the effects, and now, we are seeing that it's causing harm. People are dying, property is being damaged, we're seeing intensified fires and intensified storms that can be attributed to climate change. There is more energy in the climate system, leading to more intense events."

In their paper, the researchers try to strike a balance between alarm and optimism. On the one hand, Earth is headed into the unknown in our children's and grandchildren's lifetimes. On the other, life has long proven to be resilient. And, Williams says, in many places we are moving away from fossil fuels toward more sustainable and carbon-free energy sources. But more needs to be done.

"We've seen big things happen in Earth's history -- new species evolved, life persists and species survive. But many species will be lost, and we live on this planet," says Williams. "These are things to be concerned about, so this work points us to how we can use our history and Earth's history to understand changes today and how we can best adapt."

Author: Kelly April Tyrrell | Source: University of Wisconsin-Madison [December 10, 2018]

The largest extinction in Earth's history marked the end of the Permian period, some 252 million years ago. Long before dinosaurs, our planet was populated with plants and animals that were mostly obliterated after a series of massive volcanic eruptions in Siberia.

This illustration shows the percentage of marine animals that went extinct at the end of the Permian era by latitude, from the model (black line) and from the fossil record (blue dots). A greater percentage of marine animals survived in the tropics than at the poles. The color of the water shows the temperature change, with red being most severe warming and yellow less warming. At the top is the supercontinent Pangaea, with massive volcanic eruptions emitting carbon dioxide. The images below the line represent some of the 96 percent of marine species that died during the event. Includes  fossil drawings by Ernst Haeckel/Wikimedia; Blue crab photo by Wendy Kaveney/Flickr; Atlantic cod photo by Hans-Petter Fjeld/Wikimedia; Chambered nautilus photo by ©2010 John White/CalPhotos [Credit: Justin Penn and Curtis Deutsch/University of Washington]

Fossils in ancient seafloor rocks display a thriving and diverse marine ecosystem, then a swath of corpses. Some 96 percent of marine species were wiped out during the "Great Dying," followed by millions of years when life had to multiply and diversify once more.

What has been debated until now is exactly what made the oceans inhospitable to life - the high acidity of the water, metal and sulfide poisoning, a complete lack of oxygen, or simply higher temperatures.

New research from the University of Washington and Stanford University combines models of ocean conditions and animal metabolism with published lab data and paleoceanographic records to show that the Permian mass extinction in the oceans was caused by global warming that left animals unable to breathe. As temperatures rose and the metabolism of marine animals sped up, the warmer waters could not hold enough oxygen for them to survive.

"This is the first time that we have made a mechanistic prediction about what caused the extinction that can be directly tested with the fossil record, which then allows us to make predictions about the causes of extinction in the future," said first author Justin Penn, a UW doctoral student in oceanography.

This fossilized spiraling shark tooth is from the Helicoprion, an unusual shark that lived during the Permian. The tooth whorl was located inside the shark’s lower jaw. The fossil is on display at the Idaho Museum of Natural History [Credit: James St. John/Flickr]

Researchers ran a climate model with Earth's configuration during the Permian, when the land masses were combined in the supercontinent of Pangaea. Before ongoing volcanic eruptions in Siberia created a greenhouse-gas planet, oceans had temperatures and oxygen levels similar to today's. The researchers then raised greenhouse gases in the model to the level required to make tropical ocean temperatures at the surface some 10 degrees Celsius (20 degrees Fahrenheit) higher, matching conditions at that time.

The model reproduces the resulting dramatic changes in the oceans. Oceans lost about 80 percent of their oxygen. About half the oceans' seafloor, mostly at deeper depths, became completely oxygen-free.

To analyze the effects on marine species, the researchers considered the varying oxygen and temperature sensitivities of 61 modern marine species -- including crustaceans, fish, shellfish, corals and sharks -- using published lab measurements. The tolerance of modern animals to high temperature and low oxygen is expected to be similar to Permian animals because they had evolved under similar environmental conditions. The researchers then combined the species' traits with the paleoclimate simulations to predict the geography of the extinction.

"Very few marine organisms stayed in the same habitats they were living in -- it was either flee or perish," said second author Curtis Deutsch, a UW associate professor of oceanography.

A fossil from Morocco of a Diademaproetus, one of the trilobites that were plentiful in the world’s oceans but went extinct at the end of the Permian [Credit: Géry Parent/Flickr]

The model shows the hardest hit were organisms most sensitive to oxygen found far from the tropics. Many species that lived in the tropics also went extinct in the model, but it predicts that high-latitude species, especially those with high oxygen demands, were nearly completely wiped out.

To test this prediction, co-authors Jonathan Payne and Erik Sperling at Stanford analyzed late-Permian fossil distributions from the Paleoceanography Database, a virtual archive of published fossil collections. The fossil record shows where species were before the extinction, and which were wiped out completely or restricted to a fraction of their former habitat.

The fossil record confirms that species far from the equator suffered most during the event.

"The signature of that kill mechanism, climate warming and oxygen loss, is this geographic pattern that's predicted by the model and then discovered in the fossils," Penn said. "The agreement between the two indicates this mechanism of climate warming and oxygen loss was a primary cause of the extinction."

A fossil of a Paramblypterus, a species of fish that went extinct during the Permian. This fossil is on display at the State Museum of Natural History in Karlsruhe, Germany [Credit: H. Zell/WikiCommons]

The study builds on previous work led by Deutsch showing that as oceans warm, marine animals' metabolism speeds up, meaning they require more oxygen, while warmer water holds less. That earlier study shows how warmer oceans push animals away from the tropics.

The new study combines the changing ocean conditions with various animals' metabolic needs at different temperatures. Results show that the most severe effects of oxygen deprivation are for species living near the poles.

"Since tropical organisms' metabolisms were already adapted to fairly warm, lower-oxygen conditions, they could move away from the tropics and find the same conditions somewhere else," Deutsch said. "But if an organism was adapted for a cold, oxygen-rich environment, then those conditions ceased to exist in the shallow oceans."

The so-called "dead zones" that are completely devoid of oxygen were mostly below depths where species were living, and played a smaller role in the survival rates. "At the end of the day, it turned out that the size of the dead zones really doesn't seem to be the key thing for the extinction," Deutsch said. "We often think about anoxia, the complete lack of oxygen, as the condition you need to get widespread uninhabitability. But when you look at the tolerance for low oxygen, most organisms can be excluded from seawater at oxygen levels that aren't anywhere close to anoxic."

This roughly 1.5-foot slab of rock from southern China shows the Permian-Triassic boundary. The bottom section is pre-extinction limestone. The upper section is microbial limestone deposited after the extinction [Credit: Jonathan Payne/Stanford University]

Warming leading to insufficient oxygen explains more than half of the marine diversity losses. The authors say that other changes, such as acidification or shifts in the productivity of photosynthetic organisms, likely acted as additional causes.

The situation in the late Permian -- increasing greenhouse gases in the atmosphere that create warmer temperatures on Earth -- is similar to today.

"Under a business-as-usual emissions scenarios, by 2100 warming in the upper ocean will have approached 20 percent of warming in the late Permian, and by the year 2300 it will reach between 35 and 50 percent," Penn said. "This study highlights the potential for a mass extinction arising from a similar mechanism under anthropogenic climate change."

The study is published in the journal Science.

Author: Hannah Hickey | Source: University of Washington [December 06, 2018]

Surface melting across Greenland's mile-thick ice sheet began increasing in the mid-19th century and then ramped up dramatically during the 20th and early 21st centuries, showing no signs of abating, according to new research published in the journal Nature. The study provides new evidence of the impacts of climate change on Arctic melting and global sea level rise.

Large rivers form on the surface of Greenland each summer, rapidly moving meltwater from the ice sheet to the ocean [Credit: Sarah Das, Woods Hole Oceanographic Institution]

"Melting of the Greenland Ice Sheet has gone into overdrive. As a result, Greenland melt is adding to sea level more than any time during the last three and a half centuries, if not thousands of years," said Luke Trusel, a glaciologist at Rowan University's School of Earth & Environment and former post-doctoral scholar at Woods Hole Oceanographic Institution, and lead author of the study. "And increasing melt began around the same time as we started altering the atmosphere in the mid-1800s."

"From a historical perspective, today's melt rates are off the charts, and this study provides the evidence to prove this" said Sarah Das, a glaciologist at Woods Hole Oceanographic Institution (WHOI) and co-author of the study. "We found a fifty percent increase in total ice sheet meltwater runoff versus the start of the industrial era, and a thirty percent increase since the 20th century alone."

Ice loss from Greenland is one of the key drivers of global sea level rise. Icebergs calving into the ocean from the edge of glaciers represent one component of water re-entering the ocean and raising sea levels. But more than half of the ice-sheet water entering the ocean comes from runoff from melted snow and glacial ice atop the ice sheet. The study suggests that if Greenland ice sheet melting continues at "unprecedented rates" -- which the researchers attribute to warmer summers -- it could accelerate the already fast pace of sea level rise.

"Rather than increasing steadily as climate warms, Greenland will melt increasingly more and more for every degree of warming. The melting and sea level rise we've observed already will be dwarfed by what may be expected in the future as climate continues to warm," said Trusel.


To determine how intensely Greenland ice has melted in past centuries, the research team used a drill the size of a traffic light pole to extract ice cores from the ice sheet itself and an adjacent coastal ice cap, at sites more than 6,000 feet above sea level. The scientists drilled at these elevations to ensure the cores would contain records of past melt intensity, allowing them to extend their records back into the 17th century. During warm summer days in Greenland, melting occurs across much of the ice sheet surface. At lower elevations, where melting is the most intense, meltwater runs off the ice sheet and contributes to sea level rise, but no record of the melt remains. At higher elevations, however, the summer meltwater quickly refreezes from contact with the below-freezing snowpack sitting underneath. This prevents it from escaping the ice sheet in the form of runoff. Instead, it forms distinct icy bands that stack up in layers of densely packed ice over time.

The core samples were brought back to ice core labs at the U.S. National Science Foundation Ice Core Facility in Denver, Colo., WHOI in Woods Hole, Mass., Wheaton College in Norton, Mass., and the Desert Research Institute in Reno, Nev. where the scientists measured physical and chemical properties along the cores to determine the thickness and age of the melt layers. Dark bands running horizontally across the cores, like ticks on a ruler, enabled the scientists to visually chronicle the strength of melting at the surface from year to year. Thicker melt layers represented years of higher melting, while thinner sections indicated years with less melting.

Combining results from multiple ice cores with observations of melting from satellites and sophisticated climate models, the scientists were able to show that the thickness of the annual melt layers they observed clearly tracked not only how much melting was occurring at the coring sites, but also much more broadly across Greenland. This breakthrough allowed the team to reconstruct meltwater runoff at the lower-elevation edges of the ice sheet -- the areas that contribute to sea level rise.

Study lead author and WHOI post-doc Dr. Luke Trusel (now at Rowan University) takes field measurements of a section of ice core from Greenland before packing it for transport home [Credit: Sarah Das, Woods Hole Oceanographic Institution]

Ice core records provide critical historical context because satellite measurements -- which scientists rely on today to understand melting rates in response to changing climate -- have only been around since the late 1970s, said Matt Osman, a graduate student in the MIT-WHOI Joint Program and co-author of the study.

"We have had a sense that there's been a great deal of melting in recent decades, but we previously had no basis for comparison with melt rates going further back in time," he said. "By sampling ice, we were able to extend the satellite data by a factor of 10 and get a clearer picture of just how extremely unusual melting has been in recent decades compared to the past."

Trusel said the new research provides evidence that the rapid melting observed in recent decades is highly unusual when put into a historical context.

"To be able to answer what might happen to Greenland next, we need to understand how Greenland has already responded to climate change," he said. "What our ice cores show is that Greenland is now at a state where it's much more sensitive to further increases in temperature than it was even 50 years ago."

One noteworthy aspect of the findings, Das said, was how little additional warming it now takes to cause huge spikes in ice sheet melting.

"Even a very small change in temperature caused an exponential increase in melting in recent years," she said. "So the ice sheet's response to human-caused warming has been non-linear." Trusel concluded, "Warming means more today than it did in the past."

Additional co-authors are: Matthew B. Osman, MIT/WHOI Joint Program in Oceanography; Matthew J. Evans, Wheaton College; Ben E. Smith, University of Washington; Xavier Fettweis, University of Leige; Joseph R. McConnell, Desert Research Institute; and Brice P. Y. Noël and and Michiel R. van den Broeke Utrecht University.

This research was funded by the US National Science Foundation, institutional support from Rowan University and Woods Hole Oceanographic Institution, the US Department of Defense, the Netherlands Organization for Scientific Research, the Netherlands Earth System Science Center, and the Belgian National Fund for Scientific Research.

Source: Woods Hole Oceanographic Institution [December 05, 2018]

Ancient wildfires played a crucial role in the formation and spread of grasslands like those that now cover large parts of the Earth, according to scientists at Penn State and the Smithsonian National Museum of Natural History.

Outcrops in Pakistan provided paleosol, or fossil soil samples, used to test the role of fire in the spread of grasslands nearly 10 million years ago [Credit: Anna K. Behrensmeyer]

A new study links a large rise in wildfires nearly 10 million years ago, in the late Miocene, with a major shift in vegetation on land, as indicated by carbon isotopes of plant biomarkers found in the fossil record. Frequent, seasonal fires helped turn forested areas into open landscapes, and drove the expansion of grasslands, the researchers said.

The team developed an innovative approach to test the role of fire in the rise of early grasslands. They analyzed tracers of ancient leaves and of burned organic matter left behind in paleosols, or fossil soils, in northern Pakistan.

"The tools we use are molecules and biomarkers produced by organisms in Earth history and preserved in rocks," said Allison Karp, a graduate student in geosciences at Penn State and lead author on the paper. "We can use these as clues to figure out what was happening with climate and ecology in the past."

The new technique has broad implications as a tool for scientists seeking to answer questions about past vegetation and climate change, the researcher said.

This shows that the tool can pinpoint the location of a fire where it occurred, according to Karp. "In a paleosol record you are really capturing an integrated picture of what was happening when the soil was forming," she said.

The researchers recently reported their findings in the Proceedings of the National Academy of Sciences. Katherine Freeman, Evan Pugh University Professor of Geosciences at Penn State and Karp's adviser, is a co-author on the paper.

"This is one of the biggest ecological changes in the last 66 million years," said Karp. "None of the open grassland systems we have today existed before this transition. It was a very different looking world, especially in sub-tropical places like Pakistan."

Scientists have long studied the rise of C4 grasslands, named after plants that evolved a new way to handle photosynthesis that allows them to thrive in dry, tropical conditions and with lower amounts of carbon dioxide. These plants include modern crops like corn and sugarcane.

A drop in global carbon dioxide levels was once believed to be behind the rise of C4 grasslands. More recent research has shown that the grasses spread at different rates on different continents, indicating that regional factors, like rain patterns -- and potentially fire -- played important roles. But there had been little direct evidence that linked a rise in wildfires to this transition.

"We were interested in reconstructing fire and the expansion of grasslands in the same geologic record to see if we could find proxy evidence of the role fire played," Karp said. "We now have a nice line of observational evidence to compare to what the models have said."

Karp and her collaborators used polycyclic aromatic hydrocarbons (PAHs), found in paleosols, as fire proxies. PAHs are chemicals that are created by the burning of organic matter like wood and plants. They also are naturally found in coal and crude oil.

PAHs increased five-fold across the study area while evidence of conifer trees declined and ultimately disappeared. The heavily forested landscape opened up in two stages. Around 10 million years ago, forests were replaced by more fire-prone, open woodlands or grasslands, and between six and eight million years ago, C4 grasslands became dominant just as the quantity of fire signatures sharply increased.

Modern fire ecology can explain the process. Grasses grow faster than trees after a fire and they also help create conditions ripe for subsequent fires, promoting open landscapes. In the late Miocene, wet seasons brought on by monsoon conditions encouraged plant growth, which in turn created more fuel for fires during hot, dry seasons in Pakistan.

"The role fire played in the expansion and evolution of grassland systems in deep time is important because understanding how fire has maintained systems in the past can help us predict what may happen to these important systems in the future as climate continues to change," Karp said.

The new fire marker approach could be used to examine landscape-scale interactions between fire and vegetation for other geographic regions and climactic transitions, like glacial-interglacial transitions or catastrophic climate-change events, researchers said.

Author: Matthew James Carroll | Source: Pennsylvania State University [November 28, 2018]

Earth scientists are able to travel far back in time to reconstruct the geological past and paleoclimate to make better predictions about future climate conditions. Scientists at the Netherlands Institute for Sea Research (NIOZ) and Utrecht University succeeded in developing a new indicator (proxy) of ancient CO2-levels, using the organic molecule phytane, a debris product of chlorophyll. This new organic proxy not only provides the most continuous record of CO2-concentrations ever, it also breaks a record in its time span, covering half a billion years. The data show the present idea that rises in CO2-levels that used to take millions of years, are now happening in a century. These findings are published in Science Advances.

Cells of coccolithophore genera Gephyrocapsa grown in laboratory culture [Credit: ERC]

As CO2 increases today, it's vital to understand what impact these changes will have. To better predict the future, we must understand long-term changes in CO2 over geologic history. Direct measurements of past CO2 are available, e.g. bubbles in ice cores containing ancient gases. However, ice cores have a limited time span of one million years. To go farther back in time, earth scientists have developed various indirect measurements of CO2 from proxies e.g. from algae, leaves, ancient soils and chemicals stored in ancient sediments to reconstruct past environmental conditions.

Phytane, a new way to travel in time

A new proxy, using a degradation product of chlorophyll, allows geochemists to infer a continuous record of historic CO2-levels in deep time. Scientists at NIOZ have recently developed phytane as a promising new organic proxy that uncovers half a billion years of CO2-levels in the oceans, from the Cambrian until recent times.

Using the new proxy, they were able to make the most continuous record of ancient carbon dioxide levels ever. "We developed and validated a new way to time travel -- going farther back in time and to more places," says NIOZ-scientist Caitlyn Witkowski. "With phytane, we now have the longest CO2-record with one single marine proxy. This new data is invaluable to modelers who can now more accurately make predictions of the future."

Witkowski and colleagues selected more than 300 samples of marine sediments from deep sea cores and oils from all over the globe, reflecting the majority of geological periods in the last 500 million years.

Fossil molecules

Past chemical reactions can be 'stored' in fossil molecules, and so they may reflect various ancient environmental conditions. Geochemists are able to 'read' these conditions, such as seawater temperature, pH, salinity and CO2-levels. Organic matter, such as phytane, reflects the pressure of CO2 in ocean water or the atmosphere (pCO2).

For her research Witkowski collected seawater with fresh, modern algae to test potential indicators of the past [Credit: Caitlyn Witkowski]

Little green miracles

Although all organic matter has the potential to reflect CO2, phytane is special. Phytane is the pigment responsible for our green world. Anything that uses photosynthesis to absorb sunlight, including plants, algae, and some species of bacteria, has chlorophyll from which phytane comes. Plants and algae take in CO2 and produce oxygen. Without these little green miracles, our world just wouldn't be the same.

Because chlorophyll is found all around the world, phytane is also everywhere and is a major constituent of decayed and fossilized biomass. "Phytane doesn't chemically change over the course of time, even if it is millions of years old," Witkowski says.

Carbon isotope fractionation

CO2 of the past is estimated from organic matter, such as phytane, through the phenomenon of carbon isotope fractionation during photosynthesis. When taking up CO2, plants and algae prefer the light carbon isotope (12C) over the heavy carbon isotope (13C). They only use the heavy carbon isotope when CO2-levels in the surrounding water or atmosphere are low. The proportion between these two isotopes therefore reflects the level of carbon dioxide in the environment at the moment of growth.

This also explains why Witkowski didn't use terrestrial plants as a source for her research, exclusively using phytane from (fossilized) marine sources. The plant world is divided into so-called C3- and C4-plants, each with their own unique ratio of light-to-heavy carbon. Phytoplankton all have very similar ratios compared to their plant counterparts. Witkowski: "By choosing only marine sources, we could limit uncertainty of the phytane source in the dataset."

"In our data, we see high levels of carbon dioxide, reaching 1000 ppm as opposed to today's 410 ppm. In this respect, present day levels are not unique, but the speed of these changes have never been seen before. Changes that typically take millions of years are now happening in a century. This additional CO2-data may help us understand the future of our planet." In future research, phytane can be used to go even further back in time than the Phanerozoic, the earliest found in two billion-year-old samples.

Source: Royal Netherlands Institute for Sea Research [November 28, 2018]

New research has shed light on the origin and extinction of a giant, shaggy Ice Age rhinoceros known as the Siberian unicorn because of its extraordinary single horn.

Australian scientists believe the Siberian unicorn was a victim of climate change [Credit: WikiCommons]

An international team of researchers from Adelaide, Sydney, London, the Netherlands, and Russia, have settled a long-standing debate about the relationship of the Siberian unicorn to living rhinos, and revealed that it survived much later than previously believed, overlapping in time with modern humans.

Published in the journal Nature Ecology and Evolution and led by London's Natural History Museum, the researchers say the Siberian unicorn became extinct around 36,000 years ago. This was most likely because of reduction in steppe grassland where it lived – due to climate change rather than the impact of humans.

Today there are just five surviving species of rhino, although in the past there have been as many as 250 species.

Weighing up to 3.5 tonnes with a single enormous horn, the Siberian unicorn (Elasmotherium sibiricum), which roamed the steppe of Russia, Kazakhstan, Mongolia, and Northern China, was undoubtedly one of the most impressive.

Skeleton of the rhino at the Stavropol Museum [Credit: Igor Doronin]

Genetic analyses performed at the University of Adelaide's Australian Centre for Ancient DNA (ACAD), however, have shown that the Siberian unicorn was the last surviving member of a unique family of rhinos.

"The ancestors of the Siberian unicorn split from the ancestors of all living rhinos over 40 million years ago," says co-author and ACAD researcher Dr. Kieren Mitchell, who analysed the DNA of the Siberian unicorn. It is the first time DNA has ever been recovered from E. sibiricum.

"That makes the Siberian unicorn and the African white rhino even more distant cousins than humans are to monkeys."

This new genetic evidence overturns previous studies that suggested the Siberian unicorn was a very close relative of the extinct woolly rhino and living Sumatran rhino.

It had long been assumed that the Siberian unicorn went extinct well before the last Ice Age, perhaps as much as 200,000 years ago.

Artist’s impression of Elasmotherium [Credit: © W. S. Van der Merwe/Natural History Museum]

In this study 23 Siberian unicorn bone specimens were dated, confirming that the species survived until at least 39,000 years ago, and possibly as late as 35,000 years ago. The Siberian unicorn's final days were shared with early modern humans and Neanderthals.

"It is unlikely that the presence of humans was the cause of extinction," says co-author Professor Chris Turney, climate scientist at the University of New South Wales.

"The Siberian unicorn appears to have been badly hit by the start of the ice age in Eurasia when a precipitous fall in temperature led to an increase in the amount of frozen ground, reducing the tough, dry grasses it lived on and impacting populations over a vast region."

Other species that shared the Siberian unicorn's environment were either less reliant on grass – like the woolly rhino – or more flexible in their diet – like the saiga antelope – and escaped the Siberian unicorn's fate, though the woolly rhino eventually became extinct 20,000 years later.

Author: Robyn Mills | Source: University of Adelaide [November 27, 2018]