THE widely accepted idea that animal life evolved in the oceans before moving onto land is being challenged by a geologist who says the oceans were too salty and hot for that to have happened. He suggests that animals evolved in freshwater pools or lakes, and that the huge increase in diversity during the Cambrian explosion was triggered when they moved into the sea.
Paul Knauth of Arizona State University in Tempe bases this idea on new calculations that until about 600 million years ago the oceans would have been nearly twice as saline as they are today. It was then that large salt beds were laid down, after parts of the ocean were cut off as inland seas, which then evaporated. This, Knauth reasons, would have removed large amounts of salt from the remaining oceans.
Knauth has previously estimated ocean temperatures as far back as 2.5 billion years ago ...
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