About 444 million years ago

The end-Ordovician extinction

Ice spread, seas cooled and shallow waters drained. One of the largest extinctions in the history of animal life struck the oceans.

Deep history See it on the atlas

What happened

At the end of the Ordovician period, glaciers grew over the southern continent of Gondwana. Almost all animal life still lived in the sea, and much of it in shallow waters over the continents. As the climate cooled and sea levels changed, many of those habitats disappeared.

What the evidence shows

Modelling that combines climate cooling with the arrangement of continents at the time helps explain why this extinction was so severe for marine life.

What is uncertain

No fossil records how any particular ancestor of ours survived. A story about one animal finding new water would be fiction built on the wider evidence.
Geological change of this kind unfolds over many generations, not one lifetime.

Sources

Saupe et al. 2019. Extinction intensity during Ordovician and Cenozoic glaciations explained by cooling and palaeogeography. Nature Geoscience. (opens the publisher’s site)
What it supports: Modelling that links the severity of the end-Ordovician marine extinction to global cooling combined with the arrangement of the continents. It does not describe any particular animal’s survival.

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