Now we can blame the Chinese

For starting life in their lakes?

Conventional wisdom has it that the first animals evolved in the ocean.

Now researchers studying ancient rock samples in South China have found that the first animal fossils are preserved in ancient lake deposits, not in marine sediments as commonly assumed.

These new findings not only raise questions as to where the earliest animals were living, but what factors drove animals to evolve in the first place.

For some 3 billion years, single-celled life forms such as bacteria dominated the planet. Then, roughly 600 million years ago, the first multi-cellular animals appeared on the scene, diversifying rapidly.

The oldest known animal fossils in the world are preserved in South China's Doushantuo Formation. These fossil beds have no adult specimens - instead, many of the fossils appear to be microscopic embryos.

"Our first unusual finding in this region was the abundance of a clay mineral called smectite," said researcher Tom Bristow, now at the California Institute of Technology in Pasadena. "In rocks of this age, smectite is normally transformed into other types of clay. The smectite in these South China rocks, however, underwent no such transformation and have a special chemistry that, for the smectite to form, requires specific conditions in the water - conditions commonly found in salty, alkaline lakes."

The researchers collected hundreds of rock samples from several locations in South China. All their analyses suggest these rocks were not marine sediments.