Evidence for this glaciation comes from glacial sediments and from the extinction of groups adapted to warm climates. Glaciation was probably a major factor in at least 3 mass extinctions - in the late Ordovician, the late Devonian and the end Permian. It may also have been a factor in the extinction event at the end of the Cambrian period. Changes in sea level, which may be caused by glaciations, are commonly suggested as a cause of mass-extinctions. When sea levels change, marine habitats are disrupted or destroyed affecting any species that lived in them that are unable to move away or adapt to the new conditions.
Glaciation causes changes in sea level when seawater is taken up into the ice-sheets.
This causes oceans shrink. Changes in sea level may have other, secondary, effects. Changes in the distribution of oxygen of the oceans, or in their salinity, also have been associated with fluctuations in sea level could alter marine habitats sufficiently to cause extinction of species. Changes in sea-may have played a role in most of the mass extinctions.