About 50 million years ago the climate of our planet changed faster than at any other time in our geological record. The period lasted ... known as the Palaeocene-Eocene Thermal Maximum (PETM ...

But as the Paleocene epoch gave way to the Eocene ... labored to document the Paleocene-Eocene transition, most scientists saw it simply as a time when one set of fossils gave way to another.

If emissions continue unabated, carbon dioxide levels could meet or exceed values associated with past warm climates, such as the Cretaceous period (100 million years ago) or the Eocene epoch (50 ...