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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere
The Permian extinction came during the greatest relative drop in oxygen (and was also accompanied by a shorter-term rise in atmospheric carbon dioxide, one of the largest in Earth’s history). Both of these events took place amid the amalgamation of the largest continental landmass and the greatest volcanic event (the flood basalt eruptions left lava fields the size of Alaska). Are all of these things coincidental? That it was catastrophic is undeniable. It is certainly portrayed as the most catastrophic of the five largest mass extinctions of the past 600 million years by virtually every measure by which extinctions are compared: the percent of the fauna dying out and the effect it had on the nature of the planet’s biota.
The study of this mass extinction is ongoing. New work on Permian and Triassic strata in the Karoo of South Africa was instigated by the possibility that meteor impact was indeed the primary or contributing cause. Yet in spite of searching for impact, no evidence for impact has been discovered. Major atmospheric and oceanic oxygen-level changes coupled with global warming remain a hypothesis favored here. We will look at how those twin effects radically changed the nature of life on Earth. First, though, let’s go back to a time some 251 million years ago, in the midst of the great Permian extinction.
A voyage 251 million years ago would put us at the very end of the Permian Period. Even at the poles there is no ice. The world is hot and desert-like. There is little plant life, so little, in fact, that soil erosion has caused great dune fields of sand to form. The river systems look like those we saw in our Cambrian voyage where there were no meandering rivers, only ephemeral braided streams—the kind of sheetwash and streamflow that today is found at the bottom of glaciers of alluvial fans—places without vegetation, for it is the roots of plants that allow rivers to have bank stability, which is required for meandering rivers. This place is akin to the time before land plants. Harsh, hot winds, filled with grit, only make the atmosphere seem hotter. And hot it is—a place of high carbon dioxide and low oxygen. And it reeks of rotten eggs. Great bubbles of hydrogen sulfide are periodically emerging from the sea and larger lakes, for we will find that both of these are filled with bacteria producing this deadly gas.