The Silurian Period, 438-410 million years ago, was the time
when the colonisation of land above seal level is believed to
have started. Before then, life had been entirely confined to
the waters. The first shark scales are recorded in the early
silurian followed by the first fishes with jaws and the first
bony fishes. The earliest tracks on land (the sea scorpion "eurypterid")
date back to the Late Silurian.
During the Silurian period, vascular plants were introduced
to the world. Vascular plants are what we usually think of when
we think of plants. They differ from green algae in both the
internal and external structure in that they are adapted to withstand
the force of gravity and have the ability to retain water.