Eocene

The Eocene (IPA: /ˈiːəsiːn, ˈiːoʊ-/ EE-ə-seen, EE-o-) is a geological epoch from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era.

During the Eocene, Earth had warm climates and many plants and animals changed.

The Eocene came after the Paleocene Epoch and before the Oligocene Epoch. The start of the Eocene is marked by a time when the amount of the carbon isotope ¹³C in the air was very low. The Earth's temperature was about 27 degrees Celsius, much warmer than today.

The end of the Eocene is marked by a big change called the Grande Coupure or the Eocene–Oligocene extinction event. This change might be linked to one or more large bolides hitting Siberia and Chesapeake Bay. The rocks that mark the start and end of the Eocene are well known, but their exact dates are not exact.

Etymology

The word "Eocene" comes from two Ancient Greek words: ἠώς (ēṓs), meaning 'dawn', and καινός (kainós), meaning 'new'. This name shows that this time began many modern forms of life.

Scottish geologist Charles Lyell first used the term "Eocene" in 1833. Later, scientists like British geologist John Phillips and Austrian paleontologist Moritz Hörnes helped us learn more about this time in Earth's history. Experts later made these terms standard to study Earth's past more clearly.

Geology

The Eocene was a time of big climate changes on Earth. It started with a very warm spell called the Paleocene–Eocene Thermal Maximum. Later, the climate cooled down, but there were still warm times in the middle of the Eocene.

Scientists split the Eocene into three parts: early, middle, and late. They study rocks from this time to learn more about Earth's history. In North America, scientists use special names for plant fossils to understand how forests changed.

Palaeogeography and tectonics

During the Eocene, the continents moved closer to where they are today. At the start, Australia and Antarctica were still connected, and warm ocean currents kept Earth's climate warm. Later, Australia split from Antarctica, changing the ocean currents and making the planet cooler.

The northern supercontinent Laurasia started to break apart, with Europe, Greenland, and North America moving away from each other. In western North America, large lakes formed between rising mountains, creating important places for fossils. Meanwhile, India bumped into Asia, starting the formation of the Himalayas.

Climate

The Eocene epoch had many different climate conditions. It was one of the warmest times in Earth’s history, with very little ice at the poles. Temperatures were almost the same everywhere, unlike today when it is much colder at the poles.

The climate began to warm after the end of the Paleocene-Eocene Thermal Maximum about 56 million years ago. It reached its warmest point around 49 million years ago, called the Eocene Optimum. During this time, the oceans were about 150 meters higher than they are today because there was so little ice.

After the Eocene Optimum, the climate began to cool, and ice started to form again at the poles. By about 34 million years ago, the climate had shifted to what is called an “icehouse” climate, with large ice sheets forming in Antarctica.

Flora

During the Eocene epoch, forests covered much of the Earth, even near the poles. Tropical forests grew across Africa, South America, India, Southeast Asia, and China. Paratropical forests spread over North America, Europe, and Russia.

Polar areas also had forests. Fossils of trees like swamp cypress and dawn redwood have been found in the Arctic. Palm trees grew as far north as Alaska and northern Europe during the early Eocene.

By the end of this time, the climate cooled and dried. This caused forests to thin in some places. Grasses began to spread. Deciduous trees became more common in northern regions. Rainforests stayed only in equatorial areas such as South America, Africa, India, and Australia.

• Nuphar seeds, Nymphaeaceae, Ypresian

• Iodes tree seed, Icacinaceae, London Clay

• Mastixia tree seed, Nyssaceae, London Clay

• Ocotea tree seed, Lauraceae, London clay

• Macginitiea leaf, Platanaceae, Clarno Formation, Oregon

• Flower, Florissant Formation, Colorado

Fauna

During the Eocene, plants and marine life looked very modern. Many modern bird groups first appeared then, and the oceans were warm and full of fish and other sea creatures.

The Eocene period had the oldest known fossils of most modern mammal groups. New mammal groups came to North America, including artiodactyls, perissodactyls, and primates. These mammals had long, thin legs and hands that could grasp, along with teeth for chewing. Most Eocene mammals were small, under 10 kg, because the hot weather was easier for smaller animals. Rodents were common, and early forms of many modern mammals like horses, bats, elephants, and rodents appeared. Important fossils from this time have been found in western North America, Europe, Patagonia, Egypt, and southeast Asia. Whales became very diverse, and the first manatees and dugongs began to evolve.