Earth has seen five mass extinction events. What can we learn from them? | Daniel H Rothman

How such catastrophes occur remains mysterious. But research suggests that Earth may experience a cascade of disruptions when stressed

Five times in the last 500m years, more than three-fourths of marine animal species perished in mass extinctions. Each of these events is associated with a major disruption of Earth's carbon cycle. How such catastrophes occur remains mysterious. But recent research increasingly points to the possibility that the Earth system - that is, life and the environment - may experience a cascade of disruptions when stressed beyond a tipping point.

As world leaders gather at Cop26 in Glasgow, it makes sense to rally behind concrete goals such as limiting warming to 1.5C. If we don't meet such a goal, we'll know it soon. Mass extinctions, on the other hand, may require tens of thousands of years or more to reach their peak. But if they are indeed the result of a disruptive cascade, we must act now to prevent such a runaway process from starting.

Daniel H Rothman is a professor of geophysics at the Massachusetts Institute of Technology. He co-directs MIT's Lorenz Center, which is devoted to learning how climate works