The Silurian period was the time when reefs got their act together, grew really big and created a completely new type of ecosystem for marine life. Silurian reefs weren't built by the same types of coral around now, but by a host of tabulate and rugose corals, crinoids and sponges. As the Ordovician ice ages ended, sea levels rose, making the Silurian a period of extensive seas. Bony fish made their first appearance. Meanwhile, on land, plants became more established, and grew in a zone along the edges of rivers and lakes to give Earth its first riverine and wetland habitats.
Ordovician-Silurian mass extinction
443 million years ago
Ended: 417 million years ago
Reconstruction of the Earth in the Archean era, 3.8 billion - 2.5 billion years ago. Credit: Dr Ron Blakey, NAU Geology.
During this period the following extinction level events are thought to have occurred.
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.4 ± 1.5 million years ago (mya), to the beginning of the Devonian Period, about 419.2 ± 3.2 mya (ICS, 2004). As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a major extinction event when 60% of marine species were wiped out. See Ordovician-Silurian extinction events.
A significant evolutionary milestone during the Silurian was the appearance of jawed and bony fish. Life also began to appear on land in the form of small, moss-like, vascular plants which grew beside lakes, streams, and coastlines, and also in the form of small terrestrial arthropods. However, terrestrial life would not greatly diversify and affect the landscape until the Devonian.
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