Paleocene–Eocene Thermal Maximum

The Paleocene–Eocene thermal maximum (PETM), alternatively ”Eocene thermal maximum 1 (ETM1)“ and formerly known as the "Initial Eocene" or “Late Paleocene thermal maximum", was a geologically brief time interval characterized by a 5–8 °C (9–14 °F) global average temperature rise and massive input of carbon into the ocean and atmosphere. The event began, now formally codified, at the precise time boundary between the Paleocene and Eocene geological epochs. The exact age and duration of the PETM remain uncertain, but it occurred around 55.8 million years ago (Ma) and lasted about 200 thousand years (Ka).

The PETM arguably represents our best past analogue for which to understand how global warming and the carbon cycle operate in a greenhouse world. The time interval is marked by a prominent negative excursion in carbon stable isotope (δ¹³C) records from around the globe; more specifically, a large decrease in the ¹³C/¹²C ratio of marine and terrestrial carbonates and organic carbon has been found and correlated across hundreds of locations. The magnitude and timing of the PETM (δ¹³C) excursion, which attest to the massive past carbon release to our ocean and atmosphere, and the source of this carbon remain topics of considerable current geoscience research.

What has become clear over the last few decades is that Stratigraphic sections across the PETM reveal numerous changes beyond warming and carbon emission. Consistent with an Epoch boundary, fossil records of many organisms show major turnovers. In the marine realm, a mass extinction of benthic foraminifera, a global expansion of subtropical dinoflagellates, and an appearance of excursion taxa, including within planktic foraminifera and calcareous nannofossils, all occurred during the beginning stages of the PETM. On land, many modern mammal orders (including primates) suddenly appear in Europe and in North America.