Rethinking the scientific theorys behind mass extinctions

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As researchers continued to probe the data in recent years, however, they found that some things did not add up. New fossil analyses indicated that the Permian and Triassic extinctions were drawn-out processes spanning hundreds of thousands of years. And newly obtained evidence of the rise and fall of atmospheric carbon, known as carbon cycling, also seemed to suggest that the biosphere suffered a long-running series of environmental insults rather than a single, catastrophic strike.

That is because photosynthesis largely drives changes in the 12C-13C ratio. Plants use energy from the sun to split carbon dioxide (CO2) into organic carbon, which they exploit to build cells and provide energy; happily for us animals, free oxygen is their waste product. But plants are finicky, and they preferentially choose CO2 containing 12C. Thus, when plant life--whether in the form of photosynthesizing microbes, floating algae or tall trees--is abundant, a higher proportion of CO2 remaining in the atmosphere contains 13C, and atmospheric 12C is measurably lower.

n today's oceans, oxygen is present in essentially equal concentrations from top to bottom because it dissolves from the atmosphere into the water and is carried downward by ocean circulation. Only under unusual circumstances, such as those that exist in the Black Sea, do anoxic conditions below the surface permit a wide variety of oxygen-hating organisms to thrive in the water column. Those deep-dwelling anaerobic microbes churn out copious amounts of hydrogen sulfide, which also dissolves into the seawate





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