| Research Abstract |
Mass extinction occurred at the end of the Ordovician (440 Ma). In China, we found that a rapid decrease in biomass coincided with a significant increase in typical pyrosynthetic PAHs such as coronene.
Paleozoic life on this planet was almost lost by double mass extinction events at the Guadalupian-Lopingian (G-L) boundary (258 Ma) and the end Permian (251 Ma). We clarify coincidence of negative excursions of sulfate sulfur, some anoxic evidences, and significant decreases in marine invertebrate fossils and possible proxies for biomass including phosphorous at the end Guadalupian (〜258 Ma) in southern China. The coincidence suggests that massive release of isotopically right sulfur from the mantle, crust, or sediments to the ocean-atmosphere system, leading to significant oxygen consumption, oceanic anoxia, and the severe biotic crisis.
Our studies in southern China have revealed a remarkable sulfur and strontium isotope excursion at the end of the Permian, along with a coincident concen
… More
tration of impact-metamorphosed grains and kaolinite and a significant decrease in manganese, phosphorous, calcium, and microfossils (foraminifera). These data suggest that an asteroid or a comet hit the ocean at the end of the Permian and caused a rapid and massive release of sulfur from the mantle to the ocean-atmosphere system, leading to significant oxygen consumption, acid rain, and the most severe biotic crisis in the history of life on Earth. We also found coincidental decreases in the stable carbon isotope ratio of n-C_<27> alkane (originated from terrestrial higher plant) and marine carbonate (bulk and brachiopod shell) and coincidental increases in the strontium isotope ratio of clastics and organic carbon content during the period immediately following the end-Permian mass extinction. The data suggest that a gradual release of CO_2 occurred during the 10^4 to 10^5 years after the event due to (1) decomposition of methane hydrate caused by warming and (2) denudation of soil and sediments caused by the collapse of forests at the end of the Permian. Less
|
