Geologists studying rock formations called stromatolites found stippled, wavy markings that some claimed to be made by ancient microbes.

The rocks, widely regarded as some of the oldest fossils, are evidence of a 'microbial reef' ecosystem of similar complexity to modern coral reefs, the scientists say.

The rocks bear stippled, wavy markings that many claim are the hallmarks of colonies of ancient microbes. But others argue that the formations, which are more than 3.4 billion years old, are too old to have been made by life, which is thought only to have arisen only a few hundred million years earlier.

Abigail Allwood of Macquarie University in Sydney suggested that because diversity of life had arisen so early on on this planet, life may also have evolved on other planets like Mars (when its condition was more like Earth).

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