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The Eocene-Oligocene Boundary 33.9 million years ago was the transition from the last greenhouse period to the present icehouse climate. [17] [18] [10] At this point, when ~25% more of Antarctica's surface was above sea level and able to support land-based ice sheets relative to today, [19] CO 2 levels had dropped to 750 ppm. [20]
The Eocene–Oligocene extinction event, also called the Eocene-Oligocene transition (EOT) or Grande Coupure (French for "great cut"), is the transition between the end of the Eocene and the beginning of the Oligocene, an extinction event and faunal turnover occurring between 33.9 and 33.4 million years ago. [1]
The Drake Passage opened 33.9 million years ago (the Eocene-Oligocene transition), severing Antarctica from South America. The Antarctic Circumpolar Current could then flow through it, isolating Antarctica from warm waters and triggering the formation of its huge ice sheets.
The Oligocene is preceded by the Eocene Epoch and is followed by the Miocene Epoch. The Oligocene is the third and final epoch of the Paleogene Period. The Oligocene is often considered an important time of transition, a link between the archaic world of the tropical Eocene and the more modern ecosystems of the Miocene. [9]
Following the maximum was a descent into an icehouse climate from the Eocene Optimum to the Eocene–Oligocene transition at 34 Ma. During this decrease, ice began to reappear at the poles, and the Eocene–Oligocene transition is the period of time when the Antarctic ice sheet began to rapidly expand. [52]
The position of the Gebel-Qatrani Formation proved to be particularly problematic, which, depending on the study, belonged either entirely to the Upper Eocene or the Lower Oligocene or dated to the transition between the two time periods. [146] [147] [17] Nevertheless, a relative age position could be derived from individual fossil groups.
c. 33.9 Ma – End of Eocene, start of Oligocene epoch. c. 35 Ma – Grasslands first appear. Glyptodonts, ground sloths, peccaries, dogs, eagles, and hawks evolve. c. 33 Ma – First thylacinid marsupials evolve. c. 30 Ma – Brontotheres go extinct. Pigs evolve. South America separates from Antarctica, becoming an island continent.
It is generally accepted to have occurred during the Eocene-Oligocene climate transition (33.9 Ma onwards). [46] The onset mechanism has long been debated and remained poorly understood. On one hand, it is believed that the uplift of the Himalayas and Tibetan Plateau is the major trigger of South Asian monsoon onset, since only such elevated ...