A new study at the University of California, Riverside, has found that contrary to the belief that oceans became oxygen-rich about 600 million years ago and stayed that way till date, they actually turned oxygen poor about 499 million years ago, soon after the first appearance of animals on the planet, and remained that way for 2-4 million years.
The findings could give new insights into evolution and why some animals became extinct. "Such fluctuations played a major, perhaps dominant, role in shaping the early evolution of animals on the planet by driving extinction and clearing the way for new organisms to take their place," said Timothy Lyons, a professor of biogeochemistry.
Benjamin Gill, who worked in Lyons's lab as a graduate student, explained that some organisms were unable to cope with these fluctuations. Further oceanic oxygen affects cycles of other biologically important elements such as iron, phosphorus and nitrogen.
"Disruption of these cycles is another way to drive biological crises. Thus both directly and indirectly a switch to an oxygen-poor state of the ocean can cause major extinction of species," Gill said.
The team is now trying to find out why this phenomenon occurred. Gill said that understanding past events in Earth's distant history can help refine our view of changes happening on the planet presently.
"Today, some sections of the world's oceans are becoming oxygen-poor - the Chesapeake Bay and the so-called 'dead zone' in the Gulf of Mexico are just two examples," he said. "Understanding the ancient causes and consequences can provide essential clues to what the future has in store for our ocean."
The study appears in the Jan. 6 issue of Nature.