To See the Fate of the Oceans, Look Back a Half-Billion Years

Too Much Carbon and Not Enough Oxygen Devastated Marine Life in Ancient Times

What can the deep geological history of the oceans tell us about the future?

This question is a difficult one. In fact, it is considerably easier to start with the opposite question: What can the deep history of the oceans not tell us about the future? Understanding what ocean history is unable to tell us—and then what it can reveal—establishes the limits of our current knowledge and provides a window onto what may lie ahead.

The deep history of the oceans definitely cannot tell us about the consequences of human-caused pollution with …