From Boston, at the annual meeting of the Geological Society of America.
Global warming kicked off the Eocene epoch about 55 million years ago, but new research shows that this greenhouse phase did little for North America's plants. In contrast, warming that began 18,000 years ago caused glaciers to retreat and brought rapid shifts in the continent's flora and fauna.
The transition from the Paleocene epoch to the Eocene was marked by a rise in average temperatures of 4 to 8C in just 10,000 to 20,000 years. That initiated the so-called Paleocene-Eocene Thermal Maximum (PETM), which lasted 200,000 years.
North America's menagerie changed dramatically during the PETM, yet plant life during the Paleocene and Eocene remained similar. However, a gap in the floral record during the PETM has left open the possibility that a transient greenhouse effect introduced a dramatic but short-lived flux in plant life.