EGU2014 Thursday: “Volcanism, Impacts, Mass extinctions and Global environmental change” – a brief review of two talks.

Thursday afternoon at the EGU2014 was totally dedicated to the session “Volcanism, Impacts, Mass extinctions and Global environmental change” in which I also presented a talk. The session contained a total of eleven oral presentations covering various subject within the above mentioned topics. The first four talks were on the volcanism of the Siberian Traps and the end-Permian mass extinction event.

In the first talk, Seth Burgess presented new high-resolution geochronological data for the intrusives of the Siberian Traps. Burgess and his colleagues had used the same analysis and standards on not only zircons from the Siberian Traps, but also on zircons from the ash-layers bracketing the end-Permian mass extinction level at the GSSP Meishan in China. According to these new datings all the dated intrusives post-date the end-Triassic mass extinction event. Seth Burgess stated that although these data could be taken as “the nail in the coffin for the theory that the intrusive activity caused the mass extinction” he didn’t believe that they did. He then went on to explain that the majority of the intrusives of the Siberian Traps are situated at depths and those that have been dated are the ones that are accessible, probably producing a biased record.

This was good news for the second speaker, Henrik Svensen, who presented a talk on the sill-induced evaporite and coal metamorphism of the Siberian Traps. Svensen and colleagues showed that the Siberian Traps contain very thick sills that have been emplaced into both coal-bearing sediments and salt deposits, with the potential for degassing of both green house gases (CH4, CO2), aerosols (SO2), and ozone destructive gases (CH3Cl, CH3Br), which could explain the end-Permian biotic crisis.

A fuzzy picture of Henrik Svensen and his audience.

 

Triassic news February 2014: Origin of vivipary in marine reptiles

Vivipary, the development of an embryo inside the mother’s uterus and eventually leading to live birth, has for marine reptiles traditionally been considered to have developed in the aquatic environment. However, a new open access paper published February 12th 2014 in PLOS One by Motani et al. 2014: “Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils” provides evidence that the oldest known marine reptiles belonging to the genus Chaohusaurus (Reptilia, Ichthyopterygia) gave birth to their young through head-first birth posture, in contrast to younger (and more derived) ichtyosaurs who gave birth tail-first, just like modern whales.

Chaohusaurus, the oldest known genus of the Ichtyopterygia, inhabited the oceans during the Early Triassic, som 248 million years ago. Motani et al. 2014 found 80 new fossil skeletons of Chaohusaurus in a quarry in China. One of the specimens shows the partial skeleton of a female Chaohusaurus with three embryos, of which one is in birth position. The beautiful and exceptional fossil is pictured below, but I highly recommend reading the original paper and viewing its high resolution figures!

Figure 2 in Motani et al. 2014. The maternal specimen with three embryos.
Color coding indicates: black, maternal vertebral column, including neural and haemal spines; blue, maternal pelvis and hind flipper; green, maternal ribs and gastralia. Embryos 1 and 2 are in orange and yellow, respectively, whereas neonate 1 is in red. Scale bar is 1 cm. Abbreviations: i-v, metatarsals; 4, fourth distal tarsal; a, astragalus; c, calcaneum; cr, caudal rib; cv, caudal vertebra; d, dentary; fe, femur; fi, fibula; h, haemal spine; il, ilium; is, ischium; pb, pubis; pm, premaxilla; sr, sacral rib; sv, sacral vertebra; and ti, tibia. doi:10.1371/journal.pone.0088640.g002

The authors argue that because one of the Chaohusaurus-babies (1) lies outside the maternal body in the present specimen, this suggests that the mother had already given birth to at least one offspring before it died. They conclude that the mother likely died in labor, and because the rock containing the fossil is marine, birth most likely occurred underwater. Because the skull orientation of the embryos is head-first this suggests that viviparity in Ichthyopterygia most likely evolved in an ancestor on land, where head-first position during birth is the norm.

The authors conclude that both marine reptiles belonging to Ichthyopterygia and also Sauropterygia most likely evolved from viviparous land ancestors in the Early Triassic, at least as early as 248 million years ago. Therefore, viviparity may have already been common among terrestrial reptiles during the recovery phase from the end-Permian mass extinction.

 

 

Global warming, ocean acidification and mass extinctions

On-going anthropogenic carbon emissions has reached levels 40% higher than pre-industrial ones in 1750, due to human burning of fossil fuels. Despite international discussions and various national efforts to decrease carbon emissions, the amount of heat-trapping carbon dioxide in the atmosphere reached a record 390.9 parts per million (ppm) in 2011, according to a report recently released by the UN’s World Meteorological Organization (WMO). As a result, 30% more  atmospheric heat was kept from escaping to space than in 1990. The increased amounts of CO2 in the atmosphere has lead to a 1°C increase in average temperatures worldwide. This may not sound much, but with the long retention time of CO2 in the atmosphere the average temperature will continue to rise for a long time even if we should manage to limit our carbon emissions extensively. The World bank estimates an average temperature rise to as much as 4°C by 2060 unless we start reducing our carbon emissions significantly! The effects of such a dramatic global warming would mean serious threats to the human civilization, with extreme weather, heat waves and sea-level rise, but that is not all…

The geological record testifies to the effects of global warming. Numerous scientific articles dealing with the causes and consequences of the mass extinctions at the end-Permian (252 million years ago) and end-Triassic (201 million years ago) have provided evidence of the dire effects of intense global warming. Both events are linked to massive volcanism from large igneous provinces (LIPs) that emitted huge amounts of CO2 and methane to the Earth’s atmosphere. As discussed by Payne and Clapham (Annual Review of Earth and Planetary Sciences, May 2012) such mass extinction events in the geological record may serve as an important ancient analog for the twenty-first century! Climate change and increased temperatures, possibly coupled with destruction of the ozone layer, can account for the extinctions on land, whereas changes in ocean oxygen levels, CO₂, ocean acidification, and temperature made life difficult for marine animals, resulting in the demise of as much as 96% and 80% of all species for the end-Permian and end-Triassic events, respectively.

Recent scientific reports provide warning signals. One of the most well documented consequences of the increased CO2-levels at the end-Permian and end-Triassic events is referred to as the biocalcification crisis. The increased CO2-levels caused upper ocean acidification due to lowering of the pH of surface waters, causing problems for calcareous organisms such as calcareous phytoplankton and reef-building organisms, e.g. bivalves and corals. Scientists have long discussed the on-going coral bleeching as one result of our anthropogenic carbon emissions, but now Bednarsek et al. (Nature Geoscience, advanced on-line publication 2012) report alarming evidence of dissolution of shells on living pteropods (shell-bearing free-swimming sea-snails) in the Southern Ocean, providing further warning signals of on-going ocean acidification.

In addition, Arneborg et al. (Nature Geoscience, advanced on-line publication 2012) show increased inflow of warm and salty bottom waters to the central Amundsen shelf in Antarctica where the thinning of glaciers have persisted over the last decades. The Amundsen shelf is part of the West Antarctic Ice Sheet that contains enough ice to raise global sea level by several metres and, because it is grounded mainly below sea level, it is extra sensitive to ocean warming.

These reports, among many others, should serve as serious warning signals to world leaders that we need to take immediate action to reduce carbon emissions. So far, we have not managed to act efficiently on reducing emissions. At the UN-sponsored climate meeting in Copenhagen in 2009 the relatively weak agreement was to a non-binding target of limiting the world’s greenhouse-gas-triggered temperature increase to no more than 2°C (3.6°F) above preindustrial levels to limit the potential damage. The 2011 numbers provided by  the UN’s World Meteorological Organization (WMO) clearly show that we are failing to keep even that!

Everybody’s talking about methane…

It actually started 16 years ago when Gerald R. Dickens and his colleagues published their paper on oceanic methane hydrate dissociation and the Palaeocene-Eocene Thermal Maximum (PETM). Their hypothesis that release of methane gas stored in oceanic sediments was the cause of the negative carbon-isotope excursion at the end of the Palaeocene and hence the trigger of the global warming recorded at the PETM, got scientists working on climate change and mass extinction around the world to suddenly set their old theories aside and focus on this new one.

Burning natural gas which consists of methane to 80% (Left) and a methane molecule (right).

Today, it seems, everybody’s talking about methane, CH₄, this very potent greenhouse gas. From methane stored in clathrates underneath the ocean floor, or frozen by permafrost in the circum- Arctic or Antarctic tundra ( e.g. De Conti et al. 2012), to cattle or even farting dinosaurs during the Mesozoic, it poses a severe threat to life on Earth if released in large quantities. Hence, many scientific papers (see e.g. Payne et al. 2004 and references therein, and Ruhl et al. 2011) have argued that methane must have played a role in the end-Permian and end-Triassic mass extinctions, which are both associated with negative carbon-isotope excursions indicating input of light carbon (carbondioxide or methane from volcanoes or other sources).

My colleagues and I have studied the Triassic-Jurassic (T/J) boundary of the Denmark and compared that to a well known T/J boundary succession in England. In these two areas the carbon-isotope records exhibit three negative excursions separated by two intervals with more positive carbon-isotope values. What we have found is that the most profound floral changes on land and amongst organisms in the epicontinental sea that once covered these two areas, commenced within the first positive interval, i.e. between the first negative carbon-isotope peak and the second (most prominent) one. At the same level as the second negative carbon-isotope peak, which has been attributed to methane injection by e.g. Ruhl et al. 2011, the flora does not seem to be affected but is instead recovering, while organisms in the ocean continue to suffer. Hence our study suggests a more complex scenario…

You can read our paper (or just the abstract) or the press release.

Large herbivorous dinosaurs sustained Mesozoic greenhouse climate through flatulence?

In our society today we are very much aware of the effects of greenhouse gases on the climate. Global warming due to anthropogenic pollution has been discussed vigorously over the last decade. We spend enormous amounts of money on research and development of Carbon Capture and Storage, i.e. the possibilities of storing excess carbondioxide underground.

Geologists discuss the causes and effects massive release of carbondioxide or the four times more potent greenhouse gas methane possibly had on the climate and on life on Earth during the end-Permian and end-Triassic mass extinction events.

In a quest to find out what is normal and not normal when it comes to carbondioxide levels in the atmosphere, and the circulation of carbon on Earth, researchers have found out that our domestic cows produce some 50-100 million tonnes methane per year by gases formed in their guts.

Sheep are also environmental bad guys… 😉

Now a team of researchers lead by David Wilkinson have calculated how much methane may have been produced by large herbivorous dinosaurs, the so called sauropods including e.g. Apatosaurus, and their best estimates suggest 520 million tonnes of methane per year. A truly staggering amount as this equals the total combined methane emissions per year from all sources on Earth, i.e. from all animals and all human activities. 

     Sauropods probably had big guts containing lots of methane producing microbes!

The mean global temperature during the Mesozoic is estimated to have been 10 degrees Celsius warmer than today. Interestingly the Jurassic and Cretaceous periods are in general considered to have been periods of high diversity and productivity, both at sea and on land, despite the high levels of carbondioxide in the atmosphere.

So how come we fear carbondioxide and methane emissions today?

The key issue is probably time. Our planet; its interacting animals and plants, minerals and rocks, needs time to adapt to environmental changes. Fast injection of huge amounts of greenhouse gases to the atmosphere, whether from massive volcanism or from anthropogenic emissions, can shift climatic zones and cause major disruptions in ecosystems.

Perhaps the methane farts from the herbivorous dinosaur populations only sustained the greenhouse climate that was initiated at the end-Triassic?

Perhaps they didn’t really make things worse…just kept things normal?

Mercury new culprit in end-Permian event?

In a new paper in Geology Sanei et al. (abstract) address the potential impact of mercury loading from the Siberian Traps during the end-Permian event. Mercury is one of the most toxic elements on our planet, and one that cause much concern from an environmental perspective seing as it is very persistent and has long-ranging impact on biota.

Coupling new mercury data with their previously published carbon-isotope and coal-fly-ash events in the Permian-Triassic boundary succession of the Sverdrup Basin (Grasby et al., 2011) they propose that suppressed organic productivity due to deteriorating environmental conditions in the basin lead to catastrophic build-up of dissolved mercury in the sea.

The excess dissolved mercury could not be removed until conditions turned extreme euxinic and sulfide-mercury drawdown commenced.

It will be interesting to see if mercury-toxicity events are associated with other major volcanic events in Earth’s history!  

End-Permian extinction interval lasted <200.000 years

Super-interesting news from Science express (abstract):

High-precision U-Pb daiting of several well preserved Permian-Triassic boundary sections in South China, by Shu-zhong Shen and colleagues, show that after a 2‰ in δ¹³C over 90.000 years the extinction peak occurred just before 252.28 ± 0,08 Ma. It coincided with a -5‰ δ¹³C excursion that is estimated to have lasted up to 20.000 years. According to this study the extinctions in the terrestrial and marine realms were synchronous, and the most probable cause was massive release of thermogenic carbon dioxide and/or methane. Contemporaneous charcoal and soot-bearing layers provide evidence of widespread wildfires on land.

The entire extinction interval was according to Shen et al. less than 200.000 years, by far the shortest duration calculated for the end-Permian event so far.

End-Permian mass extinction: No problem for Parareptiles?

The end-Permian mass extinction event 250 million years ago was probably the most severe crisis in Earth history. Estimates suggest that more than 95% of life on Earth perished during this event. Marine life was hit hard. Besides the extinction of the trilobites and the tabulate and rugose corals, many other marine groups suffered near extinction including brachiopods, gastropods, cephalopods and crinoids. On land, the glossopterids, the dominant plant group in Gondwana (the southern Hemisphere) perished, and major floral changes occurred on a global scale. More than 70% of land-living vertebrate species died out.

But one group of land-living vertebrates appear almost unaffected by the end-Permian crisis, namely the parareptiles, an extinct group of reptiles, consisting of small to large tetrapods.

In a new paper in Palaeontology (read the abstract here) a group of researchers headed by Marcello Ruta recently presented various statistical analyses on diversity patterns of the Parareptilia. Their conclusion is that extinction rates for the parareptiles during the end-Permian event were no higher than before or after. However, only one clade of parareptiles crossed the Permian-Triassic boundary, and this accounted for all the Triassic parareptiles. So basically, all the other clades of parareptiles actually did die out prior to or during the end-Permian event, but as a group the parareptiles were hardly affected. It is not clear why this particular clade within the parareptiles was not affected by the end-Permian event when so many other terrestrial vertebrates were. 

The parareptiles finally did go extinct – In the Rhaetian…