Eocene Epoch

Geologic Age

• 56.0–33.9 million years ago

Eon / Era / Period / Epoch

• Phanerozoic; Cenozoic; Paleogene

Subdivisions

• Priabonian: 37.71–33.9 Ma

• Bartonian:  41.2–37.71 Ma

• Lutetian:  47.8–41.2 Ma

• Ypresian: 56.0–47.8 Ma

What happened during this time?

Geophysical

• Carbon dioxide levels begin at ~700 ppm and increase to ~900 ppm

• Oxygen levels hover around 22.5%

• Earth's surface temperatures generally rose, peaking at the Paleocene-Eocene Thermal Maximum (PETM) around 55-56 Ma

  • "...elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2." (Kender et al. 2021)

• Cooling began mid-period

• "Mean annual temperatures in southeast Australia gradually declined from ~27 °C (±4.7 °C) during the middle Eocene to ~22–24 °C (±4.7 °C) during the late Eocene, followed by a ~2.4 °C-step cooling across the Eocene/Oligocene boundary" (Lauretano et al. 2021)

• Antarctica became much colder

Biological

Flora

• Changes in vegetation are limited to the migration of plants in response to climate changes

  • Moist, balmy environment, with forests spreading; Polar forests quite extensive

  • Palm trees grow as far north as Alaska

• Between 49-50 Ma (Ypresian), the Azolla Event begins to cool the planet

• End of Eocene, continental interiors had begun to dry out; forests thinned out considerably

  • Grasses are mostly confined to river banks and lake shores

  • Cooling brought seasonal changes

  • Deciduous trees began to overtake evergreen tropical species covered large parts of the northern continents

• Earliest known carnivorous plant macrofossils found in amber (Sadowski et al. 2014)

• Earliest evidence of an orchid found in baltic amber from 55 million years ago

  • Pollinia (the pollen packets of orchids) are found attached to the leg of a fungus gnat in amber

Fauna

• Earliest known fossil primate skeleton, Archicebus achilles

• Artiodactyls became smaller (dwarfism) around 55 Ma and 53 Ma due to global warming