Until the, only one-celled organisms lived on land, but during this period, plants became abundant.

The answer is Silurian period (443 million to 416 million years ago). This was the era when life in the seas and oceans began to conquer land. This is associated with a period of warm climate, rising sea and ocean levels hence giving shallow-water grounds where reefs developed. Plants like bryophyte began to develop including the emergence of terrestrial arthropods