Eocene

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The Eocene Epoch, lasting from about 56 to 34 million years ago (55.8 ± 0.2 to 33.9 ± 0.1 Ma), is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Paleocene Epoch to the beginning of the Oligocene Epoch. The start of the Eocene is marked by the emergence of the first modern mammals. The end is set at a major extinction event called Grande Coupure (the "Great Break" in continuity), which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay. As with other geologic periods, the strata that define the start and end of the epoch are well identified,[1] though their exact dates are slightly uncertain.

The name Eocene comes from the Greek ἠώς (eos, dawn) and καινός (kainos, new) and refers to the "dawn" of modern ('new') mammalian fauna that appeared during the epoch.

Contents

Subdivisions

The Eocene epoch is usually broken into Early and Late, or - more usually - Early, Middle, and Late subdivisions. The corresponding rocks are referred to as Lower, Middle, and Upper Eocene. The Faunal stages from youngest to oldest are:

The Ypresian and occasionally the Lutetian constitute the Early, the Priabonian and sometimes the Bartonian the Late state; alternatively, the Lutetian and Bartonian are united as the Middle Eocene.

Climate

Earth's surface temperatures generally rose from the late Paleocene through the Early Eocene (~59 - 50 Ma), reaching maximum Cenozoic temperatures during the Early Eocene Climatic Optimum (EECO). Superimposed on this warming were a series of "hyperthermals". These are best described as geologically brief (<200 kyr) events characterized by rapid (in geological terms; it was far slower than either the warming predicted for the coming century or even the warming associated with the end of the last ice age) global warming and massive carbon input to the ocean and atmosphere. The most prominent of these events was the Paleocene-Eocene Thermal Maximum or Initial Eocene Thermal Maximum (PETM or IETM), which began at the Paleocene-Eocene Boundary. During this episode. Earth surface temperatures rose by 5-7 °C.[2] The PETM coincided with a major mammalian turnover on land (that distinguishes Eocene fauna from Paleocene fauna), and an extinction of many benthic foraminifera species in the deep sea. Less extreme but nonetheless pronounced hyperthermals followed the PETM, including Eocene Thermal Maximum 2 at ca. 53.7 Ma. Another hot interval occurred ~40 Ma, during the Middle Eocene Climatic Optimum (MECO) when deep sea temperatures rose about 4 °C. Coincident with MECO was a peak in CO2 and the formation of the Himilayas.[3]

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