Interval of geologic time, 490443 million years ago, the second oldest period of the Paleozoic Era .
It follows the Cambrian and precedes the Silurian . During the Ordovician, many of the landmasses were aligned in the tropics. Life was dominated by marine invertebrates, but some forms of land plants may have appeared during the middle of the period. Spores suggesting a tropical terrestrial environment have been found in rocks of that age.