Widespread, persistent oxygen-poor conditions in Earth's ancient oceans impacted early evolution of animals

ScienceDaily (2011-01-06) -- Researchers report that the transition from a generally oxygen-rich ocean during the Cambrian to the fully oxygenated ocean we have today was not a simple turn of the switch, as has been widely accepted. Their work shows the ocean fluctuated between oxygenation states 499 million years ago; such fluctuations, they say, played a major, perhaps dominant, role in shaping the early evolution of animals on the planet.