Permian-Triassic mass extinction was caused by ocean acidification

New findings of scientists from several universities published in Science show that the Permian-Triassic mass extinction (~ 252 million years ago), the greatest extinction event of all time, was caused by ocean acidification. The researchers studied boron isotopes from marine sediments in order to reconstruct seawater pH and subsequently combined these data with quantitative modeling techniques to develop a scenario for the mass extinction. Their results show that seawater pH remained relatively stable during the first phase of the extinction, but rapidly shifted to more acidic values during the second phase, which lasted ~ 10 thousand years. This acidification of the oceans had dramatic consequences for life on Earth and is thought to be associated with the release of massive amounts of carbon, related to the volcanism of the Siberian Traps. Up to 96 % of living marine species became extinct during the Permian-Triassic mass extinction and now, it has been shown for the first time that ocean acidification was the responsible mechanism.

Journal reference: Clarkson, M. O., Kasemann, S. A., Wood, R. A., Lenton, T. M., Daines, S. J., Richoz, S., … & Tipper, E. T. (2015). Ocean acidification and the Permo-Triassic mass extinction. Science348(6231), 229-232.

Image: Eruption of the Tavurvur volcano on February 13, 2009 near Rabaul, New Britain, Papua New Guinea. Source: Taro Taylor, Wikimedia Commons.

Rise of animals on Earth delayed by insufficient oxygen

Geologists of different universities have found that insufficient levels of atmospheric oxygen during the mid-Proterozoic (~ 1.8 billion to 800 million years ago) delayed the evolutionary rise of animals on Earth. They studied chromium isotope data from shallow marine Proterozoic sediments and compared them to younger Phanerozoic sediments deposited in similar environments. Their findings suggest that chromium oxidation in the Proterozoic was very limited and that oxygen levels were at most 0.1 % of present atmospheric levels. Previous estimates of atmospheric concentrations have varied greatly, but it was generally accepted that oxygen existed at Earth’s surface during the Proterozoic. The late appearance and diversification of metazoans was therefore long thought to be limited by genetic advancements and ecological innovation, but now it appears that their evolution was instead delayed by low levels of oxygen.

Journal reference: Planavsky, N. J., Reinhard, C. T., Wang, X., Thomson, D., McGoldrick, P., Rainbird, R. H., … & Lyons, T. W. (2014). Low Mid-Proterozoic atmospheric oxygen levels and the delayed rise of animals. Science346(6209), 635-638.

Image: Cirrus clouds above Warsaw, Poland. Source: Przemyslaw Idzkiewicz, Wikimedia Commons.

New details on the uplift history of the Tibetan Plateau

Research of geologists published in GSA Bulletin has revealed new information regarding the uplift history of the Tibetan Plateau, at present the highest elevated mountain range on Earth (~ 4.5 km). The scientists have reconstructed lake paleotemperatures for the Miocene and Pliocene by using clumped isotope thermometry, based on carbonate shells from gastropods in two well-studied basins in central and southwestern Tibet. Their results show that between the late Miocene and early Pliocene, paleotemperatures were up to 9 °C colder than during the mid-Pliocene and younger. Since paleotemperature records reflect changes in both climate and elevation, the scientists estimate that the Tibetan Plateau must have reached an even higher paleoelevation (~ 5.4 km) than at present. This fits well with paleontological and isotopic data from the Miocene-Pliocene indicating the presence of cold-adapted mammals in a cold, high-elevation climate.

Journal reference: Huntington, K. W., Saylor, J., Quade, J., & Hudson, A. M. (2015). High late Miocene–Pliocene elevation of the Zhada Basin, southwestern Tibetan Plateau, from carbonate clumped isotope thermometry. Geological Society of America Bulletin127(1-2), 181-199.

Image: North face of Mount Everest as seen from Tibet, China. Source: Luca Galuzzi, Wikimedia Commons.