Paleocene–Eocene Thermal Maximum

The most extreme change in Earth surface conditions during the Cenozoic Era began at the temporal boundary between the Paleocene and Eocene epochs 55.8 million years ago. This event, the Paleocene–Eocene Thermal Maximum (PETM, alternatively "Eocene thermal maximum 1" (ETM1), and formerly known as the "Initial Eocene" or "Late Paleocene Thermal Maximum",[1] (IETM/LPTM)), was associated with rapid (in geological terms) global warming, profound changes in ecosystems, and major perturbations in the carbon cycle.
Global temperatures rose by about 6 °C (11 °F) over a period of approximately 20,000 years. Many benthic foraminifera and terrestrial mammals went extinct, but numerous modern mammalian orders emerged. The event is linked to a prominent negative excursion in carbon stable isotope (δ13C) records from across the globe, and dissolution of carbonate deposited on all ocean basins. The latter observations strongly suggest that a massive input of 13C-depleted carbon entered the hydrosphere or atmosphere at the start of the PETM. Recently, geoscientists have begun to investigate the PETM in order to better understand the fate and transport of increasing greenhouse-gas emissions over millennial time scales.