How Long Can A Kitten Hold It In

The earliest known animals raised in a lake and not in the sea



have found fossils of 600 million years in a Chinese lake. It was thought that evolution began in the oceans. The oceans are a more stable and consistent than a lake. Some scientists have questioned that these are the oldest.

Fossils of animals come from the oldest known sediments of ancient lakes and the sea not as previously thought, according to a U.S. team of geologists. Scientists at the University of California at Riverside came to this conclusion after finding minerals incompatible with the marine environment in the Doushantuo rock formation in southern China, home to the oldest animal fossil found to date back 600 million years.

The results of their study are published in the online edition of the journal PNAS. Life on Earth dates back billions of years, when dominated by single celled organisms like bacteria, but animals diversified rapidly once it emerged multicellular life. It was thought that evolution began in the oceans and animal life much later adapted to the terrestrial environment.

The U.S. scientists' discovery opens a new question about where the first animals lived and how they evolved. Life in the oceans is very different, as is a more stable and consistent than a lake, according to one of the geologists, Professor Martin Kennedy. "Therefore, it is surprising that the first evidence of animals that we are associated with lakes, a much more variable than the ocean," he said.

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According to the study's lead author, Tom Bristow, the most striking finding in the southern region of China where is the Doushantuo formation was that of a clay mineral called smectite, that form requires specific water conditions, usually present in salt lakes and alkali.

scientists collected hundreds of rock samples from various locations in southern China who were subjected to geochemical analysis and x-ray "All the tests showed that the mineral and geochemical composition of the rocks were not consistent with sedimentation in the sea water," said Bristow.

addition, they found only smectite in some areas and not uniformly so, as would be expected from a marine deposits, which they say is a clear indication that the rocks that housed the fossils are of marine origin. "Taken together, these tests suggest that these ancient animals lived in a lake environment," said Bristow. Doubts



For his part, Kennedy described as "unexpected" that these early fossil came from marine sediments. "It is also possible that other agencies or older age existed in the marine environment and have not found it," he said. But the study "demonstrates that the habitat of animals can be the first more varied than previously thought and opens the exciting possibility that evolution began in the lakes, "he added.

Doushantuo formation contains no fossils adults, and most are considered embryonic cell clusters, so that some scientists have cast doubt on the question of earliest known animals.