During these periods, our global temperature also increased at rapid paces, due to volcanic eruptions and asteroid impacts.
The team of researchers from around the world examined numerous other paleocoeanographic studies to reach their conclusions.
According to the study, the level of acidity in the oceans today has only been found once in Earth's past, during the Paleocene-Eocene Thermal Maximum, which occurred about 56 million years ago.
The Paleocene-Eocene Thermal Maximum (PETM) is a period of time in Earth's past - during the Cenozoic Era, just after the boundary between the Paleocene and the Eocene epochs -- in which the global temperature of Earth increased by about 11 degrees Fahrenheit (6 deg. C) over a period of about 20,000 years.
This relates to about 0.00055 degrees (F), or 0.0003 degrees (C), per year.
National Geographic talks about the PETM in its article 'Hothouse Earth: Earth has been through this before'.
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