Approximately 443 million years ago there was an extinction resulting in the fatality of approximately 85% of all sea life, which was the majority of life at the time, given that most of the continent Gondwana was under water.Potential Causes There are three different main theories as to the cause of the extinction.The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles Lapworth in 1879, to resolve a dispute between followers of Adam Sedgwick and Roderick Murchison, who were placing the same rock beds in northern Wales into the Cambrian and Silurian periods respectively.
The geochemical data are compatible with an orogenic geodynamic environment.
Organisms found in the Ordovician period were exclusively aquatic organisms.
A small exception to this may have been extremely primitive non-vascular plants near the waterline of coasts. Even the fish that existed near the end of the Ordovician period were extremely primitive, and would be unrecognizable today.
This is likely due to high levels of carbon dioxide, which would then produce a greenhouse effect, warming the earth.
This climate change is a proposed reason for the mass extinction at the end of the Ordovician.
The main theory, with the most evidence backing it, is that the movement of the continent Gondwana into the south polar region caused global cooling, glaciation, and thus a fall in sea level.