Silurian Magic

Finally, a Foothold on Land

Published in The EarthSphere Blog

The Forgotten Origins series moves to the Silurian, where life gains a foothold on land.

The Ordovician-Silurian mass extinction was one of the biosphere’s historic low points, so the Silurian Period came in on a down note. When the Silurian recovery started 443.8 million years ago, only 15 percent of the species present during the Ordovician remained. Fortunately, the tide turned for life and things were on the upswing. The ecological void left by a catastrophic mass extinction provided evolution with plenty of opportunities to innovate.

The Gondwana supercontinent still covered much of the southern hemisphere in-and-around the South Pole. Still, warmth slowly returned to the planet, causing the magnificent southern ice sheet to shrink. Rising temperatures and melting ice led to a significant sea-level rise.

Perhaps the massive chemical weathering from plants’ initial invasion of continental landmasses had run its course, reducing carbon dioxide uptake from weathering. Such a change may have led to a net accumulation of CO2 in the atmosphere. Silurian carbon dioxide levels were higher than our modern levels, with estimates ranging from three to ten times higher.

Despite the causes of warming, life benefited from Silurian environmental conditions and thrived in the warm shallow seas and on land.

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