for National Geographic News
Weird cone- and egg-carton-shaped formations in Western Australia are almost certainly among the earliest evidence of life on Earth, according to a new study.
The 3.43-billion-year-old Strelley Pool Chert formations, called stromatolites, are sediment structures, not fossilized life forms. But their unusual features have inspired scientists to debate their origin.
Are the formations a signature of early life, or are they patterned deposits from other geological and chemical processes?
The new analysis presents several lines of evidence that support the idea that stromatolites were formed by mats of microscopic organisms (related news: "'Miracle' Microbes Thrive at Earth's Extremes").
"We provide new ways of looking at them in terms of regional scale, associated morphological distribution, and patterns and so forth," said Abigail Allwood, a geologist at the Australian Center for Astrobiology at Macquarie University in Sydney.
"The hope is we suggest to people there are many more lines than just shape that can be investigated to determine whether they are biological."
Allwood led the analysis reported in tomorrow's issue of the journal Nature.
Dawn Sumner is a geologist at the University of California, Davis, who studies stromatolites. She said Allwood and colleagues "very thoroughly document" the evidence that the stromatolites are biologic in origin.
"I would say it should lay the debate to rest," she said.
Life and Complexity
Allwood and colleagues identify seven unique stromatolite structures distributed along a 6.2-mile (10-kilometer) stretch of rock in the Pilbara region of Western Australia near Port Hedland (see a map of Australia).
Some of the structures look like upside-down ice cream cones while others resemble egg cartons.
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