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Australian Coastal Mounds May be Fossils of Earth's Oldest Life

Strangely shaped rock formations off the western Australian coast may not be rocks at all. Scientists believe the mounds are evidence of the earliest life on Earth. As VOA's David McAlary reports from Washington, they may be fossils of microbes that were alive in tidal reefs when Earth was less than one-fourth its present age.

Australian scientists waded through the water to examine several of the many mounds that follow much of the western coast of the continent in the Pilbara region. Researcher Abigail Allwood of Macquarie University in Sydney and colleagues report in the journal Nature that close scrutiny of the layered sediments in the mounds suggests that they were once living microbes.

"What we've found is a fossilized reef that was built by some of the first living organisms on this planet, almost three-and-a-half billion years ago," she said. "That's not million, it's billion. To give some sense of how old that is, it's about 58 times older than the dinosaurs and almost as old as the Earth itself."

The organisms are called stromatolites. The mounds were first discovered almost three decades ago and have been the source of spirited debate ever since. Some scientists believe they were formed chemically by hydrothermal vents, cracks in the ocean floor crust blowing heat from Earth's interior. Others argue that primitive microbes formed the piles.

The new study supports this second notion. Abigail Allwood's team trudged a 10-kilometer-long stretch of stromatolites and identified seven different types with exotic shapes. Some look like upside-down ice cream cones, others like egg cartons. Allwood told Nature magazine podcast interviewers that the formations are too complex to be chemical, although she acknowledges that their biological origin is unproven.

"Any one structure, even any one group of structures is not conclusive evidence of life in itself," she said. "The way I approached this was to look at a very large number of structures over a region and as I walked along the outcrops I began to notice that rather than just one type of structure there were actually several different distinct types and realized that they were distributed in patterns so that actually they look very similar to reefs. But they're obviously not coral reefs. They're reefs entirely built by microorganisms."

In a Nature magazine commentary accompanying the Australian study, Earth scientist Stanley Awramik of the University of California at Santa Barbara says stromatolites have suffered a lack of scientific respect as early indicators of life. He says the research may help improve their status.

Abigail Allwood says they are probably not even the oldest life on our planet.

"The diversity that you see there and the immediacy with which it arose suggests that life almost certainly arose earlier than this and this is just one of the earliest remnants that we have," she said.