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Evolution of Life was Stalled for 2 Billion Years

A coherent picture of the environmental conditions that led to the evolution of animal life is finally emerging. Scientists say that oxygen deficiency and a lack of the heavy metal molybdenum in the oceans had blocked the evolution of life on Earth for nearly two billion years.

The molybdenum record shows that the second step occurred around 600 million years ago, when the entire ocean became oxygenated, which enabled the rise of multi-cellular life called eukaryotes -- the category that includes plants, humans and other complex creatures.

"These molybdenum depletions may have retarded the development of complex life such as animals for almost two billion years of Earth history," said Timothy Lyons, a professor at University of California Riverside. "The amount of molybdenum in the ocean probably played a major role in the development of life."

Molybdenum levels are also a reliable indicator of oxygen levels in ocean chemistry.