Final answer:
The Paleocene-Eocene Thermal Maximum (PETM) occurred approximately 55.5 million years ago (Ma) and was a period of significant global warming. It is associated with changes in the diversity and distribution of organisms.
Step-by-step explanation:
The Paleocene-Eocene Thermal Maximum (PETM) occurred approximately 55.5 million years ago (Ma). This event was a short-lived period of significant global warming, characterized by a rapid release of carbon dioxide into the atmosphere. The PETM is associated with a prominent shift in the diversity and distribution of various organisms, including mammals and marine life.