brought about by the release of carbon en masse into the atmosphere and ocean systems, which led to a mass extinction of 30-50% of benthic foraminifera (single-celled species which are used as bioindicators of the health of a marine ecosystem)--one of the largest in the Cenozoic. This event happened around 55.8 Ma, and was one of the most significant periods of global change during the Cenozoic.

The middle Eocene was characterized by the shift towards a cooler