Complex sentence: While macroscopic plant life appeared early in the Paleozoic and possibly late in the Neoproterozoic, it mostly remained aquatic until sometime in the Silurian and Devonian, when it began to transition onto dry land.
Split into simpler sentences: While macroscopic plant life appeared early in the Paleozoic Eon and possibly late in the Neoproterozoic Era of the earlier eon. Plants mostly remained aquatic until sometime in the Silurian and Devonian Periods, when they began to transition onto dry land.