Wednesday, April 1, 2015

Were dinosaurs responsible for their own demise by initiating a runaway climate change?



Many scenarios have been put forward to explain the sudden disappearance in the fossil record of all non-avian dinosaurs, along with many other group of animals such as plesiosaurs, mosasaurs, ammonites and pterosaurs, at the very end of the Cretaceous period, 65 million years ago. Explanations such as starvation due to the rise of flowering plants that their stomach could not process, epidemic diseases of planetary proportion or loss of genetic diversity have long been discarded by scientific evidences. Today, most scientists adhere to the idea of a catastrophic event that caused global devastation of such magnitude many group of animals were unable to cope with. A large crater off the Yucatan peninsula (the Chicxulub crater) is believed to be the site of a massive asteroid/comet impact that wiped out the dinosaurs and 75% of life on Earth (Hildebrand et al., 1991). More recently, the Deccan traps theory, volcanic activity of unprecedented scale on the Indian subcontinent, gained ground when precise dating of the event shows it happened just before the so called K-Pg (Cretaceous-Paleogene) boundary (Schoene et al., 2015). A more exotic theory proposed dark matter in our galaxy as the prime culprit for the deed (Rampino, 2015).

However, in a new study that has just been published in the Journal of Supernatural Geological Studies, Dr. A. Zierste and co-workers came up with another plausible explanation (Zierste et al., 2015). It is well known that the Earth went through an episode of extreme “global warming” with high level of greenhouse gases during the Paleocene and Eocene periods of the Tertiary that followed the Cretaceous. The famous “Messel pit” in Germany with its exceptionally well preserved fossils of a rich tropical and subtropical fauna and flora is a vivid testimony of what the climate was at this high latitude. Zierste wondered about the mechanism that caused this greenhouse effect. Using a Tunable laser Spectrometer (TLS) similar to the one employed by the Mars Curiosity Mission (Webster et al., 2015), her team measured with high precision the isotopic ratio of light elements such as carbon and oxygen contained in sedimentary rocks from the end of the Cretaceous period to the beginning of the Eocene period. The data indicate a gradual increase in methane and carbon dioxide levels in the atmosphere that peaked right at the K-Pg boundary. But what is the origin of the high level of greenhouse gases? Zierste has a surprising answer to it: dinosaurs! These beasts were reaching gigantic proportions by the end of the Jurassic. The long-necked sauropods in particular were truly titanic, with some individuals attaining an estimated weight of 100 tons. To sustain their body mass, they have to eat tremendous amount of plants. Their stomachs were formidable fermentation chambers, producing colossal amount of methane gas that were naturally released in the Mesozoic atmosphere through gastric emanations. Methane is actually 20 times better at trapping heat than carbon dioxide. A 2006 United Nations' Food and Agricultural Organization report (http://www.fao.org/ag/magazine/0612sp1.htm ) has shown that the some 1.5 billion cows bred for milk and meat by the human population on Earth today have a non-negligible contribution to the current climate change, generating 18% more greenhouse gas than transport, in CO2 equivalent unit. Now imagine the amount of methane gas that dinosaurs could have produced. Bone histology studies have shown that the biggest dinosaurs lived to very old age, maybe 100 years and their population were most probably quite large, as they were social animals living in herds. It is difficult to estimate the total population of dinosaurs that lived on Earth at any moment of time during the Mesozoic but Zierste and her colleagues using a conservative number of about 1 billion sauropods and hadrosaurs calculated that they would have generated a staggering 20 billion metric tons of methane per year, enough to provoke a fast climate change and rapid rise of the Earth atmospheric temperature. In other words, dinosaurs perished because they induced a runaway global warming triggered by their own flatulence. Without the asteroid impact, that put an end to the continuous rise in temperature by provoking a global cooling, it is likely that the remaining 25% species of animals and plants would also have vanished and we would not be around to tell the tale.


References:

Avril Z., Peter S. G., Robert T. B., Ines L. P., Lambert J. B., Stewart M.T., Fernando E. N., Oviedo T. F., Oscar J., Lewis C. C. (2015)  Geochronological correlation of NH4 level with global atmospheric temperature at the Cretaceous/Paleogene boundary. J. of Supernatural Geological Studies, 90., 1-12.

Hildebrand, A. R., Penfield, G. T., Kring, D. A., Pilkington, M., Camargo, A., Jacobsen, S. B., & Boynton, W. V. (1991). Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico. Geology, 19(9), 867-871.

Rampino, M. R. (2015). Disc dark matter in the Galaxy and potential cycles of extraterrestrial impacts, mass extinctions and geological events. Monthly Notices of the Royal Astronomical Society, 448(2), 1816-1820.

Schoene, B., Samperton, K. M., Eddy, M. P., Keller, G., Adatte, T., Bowring, S. A., ... & Gertsch, B. (2015). U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction. Science, 347(6218), 182-184.

Webster, C. R., Mahaffy, P. R., Atreya, S. K., Flesch, G. J., Mischna, M. A., Meslin, P. Y., ... & Lemmon, M. T. (2015). Mars methane detection and variability at Gale crater. Science, 347(6220), 415-417.

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