During most of the Devonian Period, the climate was relatively mild and the continent of Euramerica, which straddled the equator at the time, set the scene for the spread of tropical and equatorial forests. The position of this land mass also meant that many communities of vertebrate animals were concentrated near the equator where the warm climate encouraged their growth and evolution.

But the end of the Devonian was marked by a period of global cooling, and severe glaciations caused the extinction of many species. This cooler period lasted for 100 million years until the beginning of the Triassic Period, when dinosaurs rose up to reign over the world.

The cooling episode may be partly explained by the emergence of photosynthetic plants in Earth’s first forests. Photosynthetic plants remove carbon dioxide – a greenhouse gas – from the atmosphere, and this may have contributed to the lower temperatures. But the “big chill” can also be explained by the positions of the continents themselves. With the major remodelling of a landmass like that involved in the formation of Pangea, oceans are closed and water currents drastically modified. Ocean currents are important temperature regulators because they redistribute heat around the planet, so a change in ocean current circulation inevitably leads to a change in the climate.
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