The Unusual Climate at the Opening of the Triassic

Australia: The Land Where Time Began

The Unusual Climate at the Opening of the Triassic

Following the mass extinction event at the close of the Permian about 250 Ma, during which an estimated 95 % of all known species went extinct, life in the oceans and on the land took millions of years to begin to flourish once again. Following other mass extinctions the survivors radiated explosively to fill the niches left vacant by those species that didn't make it through the mass extinction event. In the Early Triassic something was different. According to the author¹ a new study suggests that as life was recovering from the end Permian mass extinction another occurred, the end-Smithian Crisis occurred that is suggested to have been the result of a time of global warming like none before.

High levels of atmospheric carbon dioxide, that is often blamed on the large amount of volcanic activity in Siberia at the close of the Permian, is commonly suggested as the cause of the mass extinction, but other factors were also involved. It is commonly accepted that there was some degree of greenhouse warming associated with the mass extinction, but other factors include loss of oxygen in the oceans and loss of ozone from the upper atmosphere that allowed dangerous levels of UV radiation to strike the surface of the globe, land and water, that would have made life very difficult for life on land and in the surface waters of the oceans and all water bodies on Earth.

Coal beds from this time indicate a scarcity of plant life, what there was being generally small, the phenomenon that has been called the Lilliput Effect. Even these small plants began to die out. Yadong Sun, of China University of Geosciences, Wuhan, lead a team to study the evolution of temperatures over this time frame, reporting their findings in Nature². The research was focused on conodont teeth from deposits in southern China, that are known from deposits spread over many millions of years. As with the teeth and hard parts of other marine organisms, teeth of the conodont animal incorporate various ratios of oxygen isotopes, depending on the temperature of the water they live in.

The study of thousands of conodont teeth showed that following the end-Permian event the ocean temperatures in the equatorial region rose to 40^oC or possibly more, and this temperature ranged from the surface through the entire water column. The author¹ suggests that only the hardiest of marine organisms could have withstood such high temperatures. As there would have been a similar situation on the land it could account for the lack of plant material in deposits from that time, as indicated from coal bed formation. The results reported by the team indicates that very few fish were present during the Smithian, further strengthening the suggested lethal-heat hypothesis. The authors suggest this lethal warming probably resulted from the initial catastrophic reduction of populations in the oceans and on land during the end-Permian extinction event. The draw-down of carbon dioxide by terrestrial and marine plants was crippled in the first round of dying, having a big effect on the carbon cycle that allowed the extreme accumulation of carbon dioxide in the atmosphere that resulted in prolonged heating, that led to more extinctions.

The authors² focused their work on the equatorial regions, but they expect similar increased temperatures to apply to the high latitudes, a proposal they plan to test . The author¹ suggests the work so far carried out points to that time in the history of the Earth being one of the worst times in the entire history of life on Earth.

Sources & Further reading

Schrope, Mark. "Heat and Death." Nature Geosci 5, no. 12 (12//print 2012): 843-43.
Sun, Yadong, Michael M. Joachimski, Paul B. Wignall, Chunbo Yan, Yanlong Chen, Haishui Jiang, Lina Wang, and Xulong Lai. "Lethally Hot Temperatures During the Early Triassic Greenhouse." Science 338, no. 6105 (October 19, 2012 2012): 366-70.

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