Geology Tackles an Earlier Time That It Got Hot

About 56 million years ago, the Earth experienced something called the Paleocene-Eocene Thermal Maximum (PETM). The Earth’s atmosphere warmed by about 6.5° C, and sea surface temperatures by about 5° C. There was serious ocean acidification, which is associated with very high CO₂ levels in the atmosphere. It’s too long after the Dinosaur Killer’s cataclysmic arrival 9 million years earlier for that catastrophe to have played a role. After the PETM, it took about 170,000 years for the planet to cool back down to pre-PETM levels.

Geologists have suspected that the contemporaneous opening of the northern Atlantic Ocean by rifting might…