Not long after the dawn of complex animal life, tens of millions of years before the first of the “Big Five” mass extinctions, a rash of die-offs struck the world’s oceans.
Not long after the dawn of complex animal life, tens of millions of years before the first of the “Big Five” mass extinctions, a rash of die-offs struck the world’s oceans. Then, for reasons that scientists have debated for at least 40 years, extinctions slowed down.
A new Stanford University study shows rising oxygen levels may explain why global extinction rates slowed down throughout the Phanerozoic Eon, which began 541 million years ago. The results, published Oct. 4 in Proceedings of the National Academy of Sciences, point to 40 percent of present atmospheric oxygen levels as a key threshold beyond which viable ocean habitat expands and the global extinction rate sharply falls.
“There’s a whole set of high-magnitude extinctions earlier in the history of animal life, and then they taper off until there’s just these huge mass extinctions. And there’s never been an explanation for why we have all those high-magnitude extinctions early on,” said senior study author Erik Sperling, an assistant professor of geological sciences at Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth).
The new study reveals that even five degrees of warming – extreme for our current climate but common in Earth’s deep past – would be more than enough to trigger mass die-offs early in the Phanerozoic. The research shows this is because, in a low oxygen world, marine animals were already on the razor’s edge of their ability to breathe and maintain their body temperatures. The finding has implications for understanding the fate of ocean creatures in today’s warming world.
Read more at Stanford University
Image: Brachiopod and crinoid fossils from the Late Ordovician, about 445 million years ago. (Credit: Seth Finnegan)
