Earliest animals lived in a lake environment, rese...( RIVERSIDE Calif. Evidence for life ...)

RIVERSIDE, Calif. Evidence for life on Earth stretches back billions of years, with simple single-celled organisms like bacteria dominating the record. When multi-celled animal life appeared on the planet after 3 billion years of single cell organisms, animals diversified rapidly.

Conventional wisdom has it that animal evolution began in the ocean, with animal life adapting much later in Earth history to terrestrial environments.

Now a UC Riverside-led team of researchers studying ancient rock samples in South China has found that the first animal fossils in the paleontological record are preserved in ancient lake deposits, not marine sediments as commonly assumed.

"We know that life in the oceans is very different from life in lakes, and, at least in the modern world, the oceans are far more stable and consistent environments compared to lakes which tend to be short-lived features relative to, say, rates of evolution," said Martin Kennedy, a professor of geology in the Department of Earth Sciences who participated in the research. "Thus it is surprising that the first evidence of animals we find is associated with lakes, a far more variable environment than the ocean."

The study, published in the July 27-31 online edition of the Proceedings of the National Academy of Sciences, raises questions such as what aspects of the Earth's environment changed to enable animal evolution.

In their research, the authors focused on South China's Doushantuo Formation, one of the oldest fossil beds that houses highly preserved fossils dated to about 600 million years ago. These beds have no adult fossils. Instead, many of the fossils appear as bundles of cells interpreted to be animal embryos.

"Our first unusual finding in this region was the abundance of a clay mineral called smectite," said lead author '/>"/>