Life evolved in the ocean 3.6 billion years ago but it would be another 3.2 billion years before plants and animals colonized the land. It was during the Silurian Period (440-400 million years ago) that the ozone layer had thickened sufficiently to permit life forms to leave the protective waters of the primordial sea; of course, these plants and animals had also developed features that allowed them to survive on land.
Vascular plants, equipped with stems, first appeared in the Silurian. Stems harbor tubules which permit the transport of water and nutrients throughout the plant, protecting it's various parts from dessication; this feature was vital to the evolution of land plants. The first species, of course, colonized the shoreline, relying on the tides for nourishment; over time, root systems became for efficient and the plants lost their dependence on the sea.
The first land animals are thought to have been millipede-like creatures which also inhabited the tidal zone. Initially amphibious, they eventually became terrestrial, following the advance of the plant-line. While these pioneers were invading the coast, ammonites (ancestors of squid, cuddlefish and octopi) and the first jawed vertebrates (placoderms) were appearing in the ocean. Sharks, boney fish and lungfish would not evolve until the next geologic period, the Devonian.
