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Stratigraphy, Sedimentology and Palaeontology

GeoTalk: Hellishly hot period contributed to one of the most catastrophic mass extinctions of Earth’s history

GeoTalk: Hellishly hot period contributed to one of the most catastrophic mass extinctions of Earth’s history

Geotalk is a regular feature highlighting early career researchers and their work. Following the EGU General Assembly, we spoke to Yadong Sun, the winner of a 2017 Arne Richter Award for Outstanding Early Career Scientists, about his work on understanding mass-extinctions. Using a unique combination of sedimentological, palaeontological and geochemical techniques Yadong was able to identify some of the causes of the end-Permian mass extinction, which saw the most catastrophic diversity loss of the Phanerozoic. 

Thank you for talking to us today! Could you introduce yourself and tell us a little more about your career path so far?

Many thanks for inviting me here. I am currently working at the GeoZentrum Nordbayern, University of Erlangen-Nuremberg as a post-doc researcher.

I grew up in a small coastal town called Haiyang, east to the major city Tsingtao in North China. I moved to central China for university and majored in Geology at the China University of Geosciences (Wuhan) in 2004-2008.

This was followed by an exciting, 5 years split-site PhD program in which I spent two and a half years in China for field work and palaeontological training; half a year at Erlangen Germany for stable isotope and geochemical studies and the final 2 years at the University of Leeds, UK for training in sedimentology.

After my PhD, I successfully applied a fellowship from the Alexander von Humboldt Foundation and become an honourable Humboldtian.

In late 2015, two years after my PhD, I had 31 peer-reviewed papers including two in Science but was not fully prepared for the job market. It was already near the end of my fellowship. I only applied for one job—the O.K. Earl postdoc fellowship at the California Institute of Technology, US, but I didn’t get it. Completely unprepared for the situation, I was unemployed for about half a year.

I considered this the first setback in my early career. It taught me a valuable lesson; since I applied various research funding and fellowships and have never failed.

In early 2016, I was offered a postdoc position in a big project from the German Science Foundation (DFG forschergruppe) at Erlangen. I am very happy to be involved in the project and work again with many German and European colleagues.

Meet Yadong, pictured on fieldwork in the Himalayas. Credit: Yadong Sun.

During EGU 2017, you received an Arne Richter Award for Outstanding Early Career Scientists for your work understanding the end-Permian mass extinction. Could you tell us a little bit more about this period during Earth’s history?

The end-Permian mass extinction, which happened 252 million years ago, is the most devastating crisis seen in the Phanerozoic (the period of time during which there has seen life on Earth). However, the ultimate killing (or triggering) mechanism of this mass extinction is not fully understood and has been intensely debated for years.

Many fossil groups, in the ocean and on land were completely wiped out. The end-Permian mass extinction had profound influence on the evolution of life on Earth; such was the scale of the dying at this time. Extinction losses appear non-selective; virtually no groups escaped unscathed.

In the oceans some of the most abundant organisms such as the brachiopods (two-shelled organisms), radiolaria and foraminifera were almost (but not quite) eliminated whilst the rugose corals, tabulate corals, goniatites and trilobites were forever lost.

On land, the dominant herbivorous animals, the pareiasaurs, together with the gorgonopsids, the top predators, were lost. They lived in a world in which the dominant trees were the seed-bearing gymnosperms (e.g. glossopterids, gigantopterids, cordaites). All these groups, together with many other animals, including diverse insect groups, failed to survive the extinction.

After the mass extinction, the Early Triassic world was a time of extraordinary low diversity with the same monotonous communities found everywhere. For example, there is a 5 million year gap during which corals are not found in the rock record.

On land this included assemblages dominated by a shrub-like tree fern called Dicroidium, whilst the dominant animal was Lystrosaurus a pig-sized herbivore, belonging to a group called the dicynodonts.

In the world’s oceans, in the immediate aftermath of the extinction, it was the mollusks which occurred in the greatest numbers; a bivalve called Claraia was prolifically abundant just about everywhere.

It took an unusually long time (around 4-5 million years) for the biosphere to start recovering from the end-Permian mass extinction. This is much longer than after other mass extinctions and has lead scientists to speculate that the harsh conditions, responsible for the extinction in the first place, may have persisted for long afterwards.

At the same time, ocean chemistry was probably very different to modern day Earth. The oxygen levels in seawater were very low.

Despite the debate, what do scientists know about the causes of the end-Permian extinction?

The causes of the end-Permian mass extinction are, as a matter of fact, not perfectly understood. There are many different hypotheses. The key is to test the different hypotheses.

At the moment, we know with quite some certainty that anoxia (no free oxygen in seawater) and high temperatures both likely contributed to the end-Permian mass extinction.

Around the time of the extinction, there was massive volcanic activity in present day Siberia, known as the Siberian Traps. The lavas they left behind are known as the Siberian flood basalts. The eruption of the super volcano triggered global warming, voluminous volcanic CO2 inject to the atmosphere could lead to ocean acidification. This is because CO2 reacts with water and becomes carbonic acid (CO2 + H2O ↔ H2CO3). This is a very new and popular hypothesis to explain the mass extinction.

However, I myself am not fully convinced by the ocean acidification theory for the end-Permian mass extinction because there is a lot of evidence for carbonate over-saturated conditions at this time too. Carbonate saturated conditions mean that seawater contains very high concentrations of species such as CO32- and HCO3. They easily combine with Ca2+ and precipice as limestone and calcite cements. High concentrations CO32- and HCO3 have a buffering effect which inhibit the reaction forming carbonic acid. Therefore, it is not really possible to have ocean acidification and carbonate over-saturation at the same time. More detailed studies are needed to investigate this paradox.

In the past, some scientists proposed a sudden cooling or bolide impact as potential causes for the extinction, but these theories are no longer popular because of a lack of evidence.

In your presentation at EGU 2017 you spoke about how the extinction was accompanied by a rapid temperature rise, from 25 °C to 32 °C. How were you able to establish that such a significant temperature rise occurred?

I use oxygen isotope thermometry from conodonts: an extinct eel-like creature. Oxygen has two isotopes—18O and 16O. The ratio of the two isotopes in an animal is proportional to temperature from the oxygen isotope ratio of the water they ingest.

Reconstruction of temperatures for the end-Permian mass extinction is not easy since most shelly fossils died out. Those preserved are often subject to burial changes and therefore no longer preserve the original environmental information.

On the other hand, conodonts survived the end-Permian mass-extinction and are ideal for oxygen isotope analyses. They are very tiny (typically ~300 micro meter long) and consist of biogenic apatite. Apatite has 4 very robust P-O chemical bonds and very difficult to be altered after burial. Therefore, measuring oxygen isotope ratio of conodonts could help solved the problem.

However, because conodonts are so small and rare in rocks, I had to collect 2 tons of carbonate rocks dissolve the rock in acetic acid and pick the conodonts one by one under a binocular microscope, to get a big enough sample! It was a lot of work and required a lot of patience.

A Triassic conodont from south China. Credit: Yadong Sun.

That certainly sounds like painstaking work! Once the tedious task was completed, how were you able to link the temperature records you deciphered from the conodonts with the mass extinction?

All living creatures have a thermal threshold, also called thermal tolerance – the temperature range which they are able to tolerate to survive. It varies significantly amongst different groups. Most animals, on land or in the oceans, cannot live in environments that are consistently hotter than 47 °C. However, certain groups of desert ants and scorpions have developed special mechanisms and can survive 53 °C for a very brief time. Another example is the elevated seawater temperatures which contribute to high death rates of corals.

High temperatures supress photosynthesis. In most C3 plants, at temperatures above 35°C, photorespiration exceeds photosynthesis, wasting the energy generated by the plants.  in most C3 plants. Under such circumstances, C3 plants will stop growing and probably die shortly after. Maximum growth rates of single-celled algae in the ocean are normally achieved below 40°C.

A significant rise in seawater temperatures has many negative effects. One of them is that the amount of oxygen dissolved in seawater decreases as temperature rises, while animals use up more energy to perform even the simplest tasks. . This is one reason for which most marine groups prefer environments < 35°C.

These observations tie mass extinctions with temperature increase.

For our study, once the oxygen isotope ratios of conodonts are measured, we can use it in an equation to calculate the absolute temperature of the seawater at the time. The results show significantly higher ocean temperatures than today. We know the equation explains the relationship accurately because it was established in aquariums where scientists raise fishes in controlled temperatures. As temperatures are known, they measure the oxygen isotope of the water and fish teeth and established the oxygen isotope—temperature equation.

What do your findings mean for the current understanding of the causes of the mass-extinction?

This is an excellent question. There are quite some studies which postulate global warming as a potential killing mechanism for the end-Permian mass extinction. There is a link between the timing of the massive eruptions of the Siberia Large Igneous Province and the end-Permian mass extinction, which has led scientists to propose different warming scenarios. They are all correct, but they are not able to show direct evidence for their hypotheses or quantify the temperature change.

Our data show the worst-case scenario in terms of temperature rise and the mass mortality of species. This does not necessarily imply high temperatures killed everything because many adverse environmental conditions could trigger synergetic effects (for example low oxygen levels). Our study set an example for comparison.

Our results mean that rapid warming, such as what we are encountering at present, is truly worrying.

Yadong, thank you for speaking to me about your reasearch. As an award winner with an impressive career so far, what advice do you have for early career scientists?

Europe is probably the best place in the world for young scientists. It provides considerable fair funding opportunities and many possibilities to work with other scientists in the EU.

However, it is undeniable that fixed positions in academia are rare and highly competitive. It is always the best to go to meetings/conferences at least once a year to showcase your research, meet colleagues and seek collaboration opportunities.

Research projects nowadays are much more complex. Many tasks cannot be done by one person or one team. The success of a young scientist cannot be achieved without the support of senior scientists as well as the community.

Also don’t be shy to contact people and always be prepared for the job market. In the post-doc stage, if your project is very challenging, the best strategy is to work on some small projects on the side and keep publishing.

Interview by Laura Roberts Artal (EGU Communications Officer)

References

Sun, Y. Climate warming during and in the aftermath of the End-Permian mass extinction, Geophysical Research Abstracts, Vol. 19, EGU2017-2304, 2017, EGU General Assembly, 2017

How certain plants survive mass extinction events: study

How certain plants survive mass extinction events: study

We often read about Earth’s mass extinction events and how they wiped out vast numbers of animal species, leaving survivors to evolve and repopulate the planet. But it’s rarer to hear about how plants managed these catastrophes.

A new study published last month by a team at University College Dublin, Ireland, in the journal Nature Plants shows how plants with thicker, heavier leaves were more likely to survive the Triassic-Jurassic mass extinction caused by an episode of global warming 200 million years ago – around the time when dinosaurs came to dominate the planet. The extinction event is known to have had a massive impact on life, both on land and in the oceans, with an estimated half of species on Earth going extinct at the time.

“Previously we knew a bit about plant survival in terms of their abundance – whether they are present or absent in fossil record,” says the study’s lead author Wuu Kuang Soh, of University College Dublin, “but we didn’t know how they survived or the intrinsic factors of plants that contributed to their survival.”

By looking at fossilized leaves of two plant groups uncovered in Greenland, the authors suggest that the reason for some plants’ survival is that those with heavier leaves were more resilient to environmental stressors such as high air temperature and rising carbon dioxide.

According to Barry Lomax, a lecturer in Environmental Science at the University of Nottingham, UK, who was not involved in the research, “being able to establish that different plant groups respond differently to stress, and that their capacity to adapt to this stress is reflected in their propensity for survival, is a great piece of detective work.”

New proxy development

The work presented in this study – a joint research effort by University College Dublin and Macquarie University, Australia – relied heavily on the development of a new proxy i.e. a physical characteristic which is used to infer details about some related, but immeasurable, trait. By showing how the thickness of a plant’s leaf cuticle (the protective layer covering a leaf) is related to the leaf mass per unit area (LMA) in modern leaves, the team were able to use their fossils to identify how heavy the paleo leaves were for their size.

Macrofossil of 200 million years old Triassic ginkgo, Sphenobaiera spectabilis. Used with permission of the study authors (Credit: Mark Wildham).

For some scientists, this development itself is the study’s highlight. “I think the key finding of the work is that it gives us another set of tools to unpick how plants have responded to large scale perturbations in the carbon cycle which have influenced climate,” says Lomax.

By using the new proxy for LMA the authors were able to look at changes in two plant groups – Ginkoales (an gymnosperm order – see image) and Bennettitales (a now extinct order of seed plant)– across the Triassic-Jurassic mass extinction, and discover their opposing fates; the former flourishing and the latter experiencing sharp ecological decline.

“We found that plants with higher LMA had a higher chance of survival than plants with lower LMA during this global warming induced mass extinction event” says lead author Soh.

Commenting on the study, Charilaos Yiotis, a plant physiologist at University College Dublin who did not participate in the research, says that “under the greenhouse conditions of the Triassic-Jurassic Boundary – or, may I add, under near-future greenhouse conditions – plants with fast leaf turnover rates (low LMA) are outcompeted by those adopting more “conservative” strategies like robust, low turnover leaves (high LMA).” The turnover rate Yiotis refers to is the time taken for leaves to be produced and then fall.

“The spectrum describes how “fast” or “slow” the plant is turning over its nutrient resources,” adds Dana Royer, a paleobotanist at Weslayan University, Connecticut, who peer-reviewed the paper for Nature. “At the fast-return end (low LMA), plants have high photosynthetic rates, high nutrient contents, short-lived (deciduous, for example) and cheaply built leaves. This is the live-fast-die-young strategy. At the slow-return end (high LMA), plants show the reverse.”

The current mass extinction

The study’s findings are important in relation to the sixth mass extinction event which is currently underway. Scientists believe that a similar extinction process to those in the past is now taking place, as the variety of life on land gives way to the seemingly unstoppable human developments of agriculture, industry, and urbanisation. By looking at the paleo-evidence the authors tentatively suggest that today’s plant communities which host thicker, heavier leaves (high LMA) may be better adapted to deal with the current episode of anthropogenic warming, and therefore have a better chance of future ecological success than plants with lighter leaves (low LMA).

“More specifically, plants that can have leaves with both low and high LMA appear to do well after surviving a catastrophic mass extinction episode,” says Soh. “Our finding is important because it means that plants with flexibility in LMA will be the favourite to flourish during future global warming.”

“A shift to higher LMA is common for plants when they are exposed to high CO2” says Royer, “so the fact that the authors are finding the same response in a “natural” experiment – albeit 200 million years ago – lends support to the idea that we should expect a similar response in our own future.”

Further looking to the future, University College Dublin’s Charilaos Yiotis finds it alarming that most plants of economic importance today would probably never have made it through the Triassic-Jurassic Boundary.

“At a time where humanity’s biggest challenge is to feed an ever-growing human population,” he says, “this study should make us think again about how big a threat climate change is to future food security.”

By Conor Purcell, a Science & Nature Writer with a PhD in Earth Science.

Conor has previously worked with the authors of this paper, but not on the project itself. He can be found on twitter @ConorPPurcell and some of his other articles at cppurcell.tumblr.com.

References

Soh, W.K., Wright, K.L, Bacon, T.I., et al., Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event, Nature Plants, 3, doi:10.1038/nplants.2017.104, 2017.

Editor’s note: This blog post provides a summary to a research paper that is paywalled, unlike other scientific articles featured on GeoLog. The EGU supports and promotes open access, publishing 17 open access journals and having endorsed Open Access 2020, an initiative to promote the large-scale transition to open access publishing. Since research in the realm of palaeontology and evolutionary biology is rarely featured on GeoLog, an exception was made on this occasion to publish a story on a scientific paper not accessible to all. The lead author of the study is happy to be contacted with questions about the research; if you’d like to find out more please email Wuu Kuang Soh (wuukuang@gmail.com).

 

 

September GeoRoundUp: the best of the Earth sciences from around the web

September GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major story and what you might have missed

This month has been an onslaught of  Earth and space science news; the majority focusing on natural hazards. Hurricanes, earthquakes and volcanic eruptions have been dominating headlines, but here we also highlight some other natural disasters which have attracted far fewer reports. Quickly recap on an action-packed month with our overview, complete with links:

Hurricanes

Thought the Atlantic hurricane season is far from over, 2017 has already shattered records: since 1st June 13 storms have been named, of which seven have gone onto become hurricanes and two registered as a category 5 storm on the Saffir-Simpson Hurricane Wind Scale. In September, Hurricanes Irma, Katia and Jose batter Caribbean islands, Mexico and the Southern U.S.; hot on the heels of the hugely destructive Hurricane Harvey which made landfall in Texas and Louisiana at the end of August. Images captured by NASA’s Operational Land Imager (OLI) on the Landsat 8 satellite show the scale of the damage caused by Hurricane Irma; while photos reveal the dire situation unfolding in Puerto Rico after Hurricane Maria.  OCHA, the United Nations Office for the coordinate of Human Affairs, released an infographic showing the impact the 2017 hurricane season has had on Caribbean islands (correct of 22nd September).

Earthquakes

At the same time, two powerful earthquakes shook Mexico in the space of 12 days causing chaos, building collapse and hundreds of fatalities.

Rumbling volcanoes

In the meantime, all eyes on the Indonesian island of Bali have been on Mount Agung which has already forced the evacuation of almost 100,000 people as the volcano threatens to erupt for the first time in 54 years. Unprecedented seismic activity around the volcano has been increasing, though no eruptive activity has been recorded yet.

Further south, the government of Vanuatu, a South Pacific Ocean nation, declared a state of emergency and ordered the evacuation of all 11,000 residents of Ambae island, as activity of its volcano, Manaro, increased. The New Zealand Defence Force (NZDF) sent an aircraft to fly over the volcano on Tuesday and discovered plumes of smoke, ash and volcanic rocks erupting from the crater.

Map of volcanic hazards for Ambae in Vanuatu. Credit: Vanatu Meteorology & Geo-hazard Department (vmgd).

The rainy season floods

The summer months mark the onset of the rainy season in regions of Sub-Saharan Africa which experience a savanna climate. Across the Arabian Sea, including the Indian subcontinent and Southeast Asia, also sees the onset of the monsoon.

Since June, widespread flooding brought on by heavy rainfall has left 56 dead and more than 185,000 homeless in Niger, one of the world’s poorest countries. But the crisis is not restricted to Niger, throughout the summer floods (and associated land and mudslides) in Africa are thought to have claimed 25 times more lives than Hurricane Harvey did.

Meanwhile Mumbai struggled when the heaviest rainfall since 2005 was recorded on 29th August, with most of Northern India experiencing widespread flooding. So far, the UN estimates that 1,200 people have lost their lives across Nepal, India and Bangladesh as a result of the rains. The Red Cross estimates that at least 41 million people have been affected by the flooding and causing the onset of a humanitarian crisis.

Record breaking temperatures and fires

Australia’s record-breaking spring heat (Birdsville, in Queensland’s outback, broke a weather record as temperatures hit 42.5C and Sydney recorded its hottest ever September day) combined with an unusually dry winter means the country is bracing itself for a particularly destructive bushfire season. Already fires rage, uncontrolled (at the time of writing), in New South Wales.

The western United States and Canada suffered one of its worst wildfire seasons to date. Earlier this month, NASA released a satellite image which showed much of the region covered in smoke. High-altitude aerosols from those fires were swept up by prevailing winds and carried across the east of the continent. By 7th September the particles were detected over Ireland, the U.K and northern France, including Paris.

Europe’s forest fire has been hugely devastating too. Much of the Mediterranean and the region North of the Black Sea continues to be in high danger of forest fires following a dry and hot summer. Fires are active in the Iberian Peninsula, Greece, and Germany (among others). Over 2,000 hectares were recently scorched by wildfires in the central mountainous area of Tejeda in Gran Canaria.

Links we liked

  • This month saw the end of NASA’s Cassini spacecraft and ESA’s Huygens probe’s spectacular journey to Saturn. After two decades of science, the mission ended on 15th September as the spacecraft crashed into the giant planet.
  • The last day of August marks the end of the Greenland snow melt season, so September was busy for scientists evaluating how the Greenland ice sheet fared in 2017.
  • “Few disciplines in today’s world play such a significant role in how society operates and what we can do to protect our future,” writes Erik Klemetti (Assoc. Prof. at Denison University), in his post on why college students should study geology.
  • The BBC launched The Prequel to its much anticipated Blue Planet II, a natural history progamme about the Earth’s oceans. Narrated by Sir Sir David Attenborough, the series will featured music by Hans Zimmer and Radiohead. The trailer is a true feast for the eyes. Don’t miss it!

The EGU story

Is it an earthquake, a nuclear test or a hurricane? How seismometers help us understand the world we live in.

Although traditionally used to study earthquakes, like the M 8.1 earthquake in Mexico,  seismometers have now become so sophisticated they are able to detect the slightest ground movements; whether they come from deep within the bowels of the planet or are triggered by events at the surface. But how, exactly, do earthquake scientists decipher the signals picked up by seismometers across the world? And more importantly, how do they know whether they are caused by an earthquake, nuclear test or a hurricane?

To find out we asked Neil Wilkins (a PhD student at the University of Bristol) and Stephen Hicks (a seismologist at the University of Southampton) to share some insights with our readers earlier on this month.

Imaggeo on Mondays: A prehistoric forest

Imaggeo on Mondays: A prehistoric forest

This stunning vista encompasses the south-western wilderness of Tasmania as seen from the Tahune air walk 60 m above the Huon river valley. In front lies the beginning of a huge UNESCO World Heritage Site, covering almost a fourth of the area of Tasmania. The site mostly consists of a pristine, temperate rainforest of Gondwanan origin that is home to the tallest flowering trees in the world; Eucalyptus spp. reach up to 100 m height in this region.

“I have never tasted the sense of a more remote place than this one. Give me more,” says Vytas Huth, who captured this stunning shot.

Gondwana was a supercontinent, consisting of present day Africa, South America, India, Madagascar, Australia and New Zealand. It formed when the even larger supercontinent of Pangaea broke up 250 million years ago.

Slowly, Gondwana started to break apart too. India tore away first, followed by Africa and then New Zealand. By the end of the Cretaceous, 65 million years ago, only South America, Australia and Antarctica remained joined.  It took a further 20 million years before Australia and Antarctica separated.

By the time Australia started being pulled northwards, the first glaciers were forming on Antarctica, as it began freezing over. Atop the old rocks which made up its bulk, animals and plants of ancient origin, travel northwards with the Land Down Under.

Because India and Africa broke away from the supercontinent so early on, few hallmarks of ancient Gondwana wildlife are left in their present biodiversity. In contrast, Australia and Tasmania remained connected to Antarctica and South America much longer and there are clear similarities in species across these continents.

“Fossil evidence suggests that temperate rainforest once extended across Australia, Antarctica, South America and New Zealand around 45 million years ago. Such fossils and the surviving species in Tasmania provide evidence of the ancient link to Gondwana”, reports the Tasmania Parks & Wildlife Service.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.