The Eocene Period, birds ruling a warm world

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Article 30: In the Early Eocene, the Earth is a greenhouse world. Life is small and living in cramped jungles. There is nothing over the weight of 10 kilograms. At the top of the food chains are huge birds.

The Eocene Period of the Earth’s history spans 22 million years, from 56 to 34 million years ago.

Eocene ecosystem
Eocene ecosystem, digital art. Credit: Emilio Rolandi

The Early Eocene is thought to have had the highest mean annual temperatures of the last 65 million years, with temperatures about 30° C, relatively low temperature gradients from pole to pole, and high precipitation in a world that is essentially ice-free. The Eocene oceans are warm and teeming with fish and other sea life.

The Earth is a greenhouse world.

Greenhouse gases, in particular carbon dioxide and methane, play a significant role during the Eocene in controlling the surface temperature. Methane is a greenhouse gas that has a drastic effect on the climate. In comparison to carbon dioxide, methane has much higher consequences with regards to temperature, as methane has ~34 times more effect per molecule than carbon dioxide on a 100-year scale: it has a higher global warming potential.

Due to the warmer climate and the sea level rise associated with the early Eocene, more wetlands, more forests and more coal deposits are available for methane release. Comparing the early Eocene production of methane to current levels of atmospheric methane, the early Eocene is able to produce triple the amount of the current methane production.

A Sunday afternoon in the Eocene. Credit: Kim Thompson, artist

In the Early Eocene, life is small and living in cramped jungles, much like in the Paleocene. There is nothing over the weight of 10 kilograms. Among them are early primates, whales and horses along with many other early forms of mammals.

At the top of the food chains are huge birds, such as Gastornis. It is the only time in recorded history that birds rule the world.

The Eocene bird Gastornis was neither a predator nor a worm catcher, but a gentle, herbivorous giant.

Eocene fauna
Restoration of Eocene fauna of North America, on a mural made for the Smithsonian Museum. Credit: Jay Matternes

It is an important time of plate boundary rearrangement, causing significant effects on oceanic and atmospheric circulation and temperature. The northern supercontinent of Laurasia begins to break up, as Europe, Greenland and North America drift apart.

Middle Eocone
50 – 55 million years ago India begins to collide with Asia, forming the Tibetan plateau and the Himalayas. Australia, which was attached to Antarctica, begins to move rapidly northward.

In the middle of the Eocene, the separation of Antarctica and Australia creates a deep water passage between those two continents, the CircumAntarctic Current. This changes oceanic circulation patterns and global heat transport, resulting in a global cooling event at the end of the Eocene. Following the maximum of the highest mean annual temperatures is a descent into an icehouse climate. During this decrease, ice begins to reappear at the poles and the Eocene-Oligocene transition is the period of time where the Antarctic ice sheet begins to rapidly expand. The lower temperatures cause a shift towards increasingly open savannah-like vegetation, with a corresponding reduction in forests.

Thanks to the University of California, Berkeley, Museum of Paleontology

ShantiShanti is a regular contributor to Osho News
All essays of this series can be found in: At Home in the Universe
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