This was a time of explosion of life. There was an explosion of marine life. Hard-shelled organisms developed, so that we have an extensive fossil record of evolution during this period. Trilobites, sponges, snails, clams and corals. The explosion may be related to the development of sex.
Prokaryotes are asexual.
The development of sexual reproduction would lead to a rapidly evolving community. Ordovician period Fish begin to populate the seas. Coming to land . In the Silurian period, plants began to occupy the land. Three requirements are needed for this development.