Over millions of years, most living organisms suffocated in oxygen-deprived oceans. In the aftermath, modern vertebrates conquered the world.

ByCody CottierJanuary 23, 2021 9:00 AM

(Credit: Rich Carey/Shutterstock)

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We think of mass extinctions as brief moments of havoc — profoundly devastating but over within a geologic instant. The Devonian, the second of the so-called “Big Five,” defies this notion. If the other great die-offs are short stories of death and destruction, this one is an epic akin toWar and Peace. Even that paradoxical title seems fitting: The Devonian extinction ravaged Earth on and off for 25 million years, and although it ultimately killed three-quarters of all species, it also cleared the way for a new balance of animal life that endures to this day.

The extinction began roughly 380…