Brutonyx

THE AGES OF THE EARTH CHAPTER FOUR SILURIAN The Ordovician ended about 444 million years ago in a mass extinction, likely a result of the cooling of the climate, which might have been caused by the first land-growing plants, small as they were, increasing the amount of oxygen and reducing the carbon dioxide in the atmosphere. But the planetary ecosystem soon stabilized and reversed this. The next period, the Silurian, started with a seriously warming climate. But over the period there were a large number of drastic warming-up and cooling-down phases. Life rediversified rapidly after the extinction event. This is the period during which life finally fully conquered the land. Before this, the continents were barren sheets of rock, with at most a thin green film of algae and moss-like plants around the seashores or along inland lakes and ponds. But in the Silurian, vascular plants evolved – they had strengthened vessels that carried sap containing nutrients through their stems.