Newly unearthed microbial fossils suggests life thrived on Earth earlier than previously thought.

A team of Australian researchers have discovered 3.7 billion-year-old stromatolites -- fossil structures formed by ancient microbes -- in the oldest sedimentary rocks on the planet. The fossils were found in the Isua Greenstone Belt at the border of Greenland's icecap. Recent melting exposed the fossils to the sea and made them visible to a team of scientists looking for ancient evidence of life.

The discovery pushes back the appearance of stromatolites in the fossil record by 220 million years.

"The significance of stromatolites is that not only do they provide obvious evidence of ancient life that is visible with the naked eye, but that they are complex ecosystems," Allen Nutman, a professor at the University of Wollongong, said in a news release.

"This indicates that as long as 3.7 billion years ago microbial life was already diverse," Nutman said. "This diversity shows that life emerged within the first few hundred millions years of Earth's existence, which is in keeping with biologists' calculations showing the great antiquity of life's genetic code."

Researchers say the discovery will force planetary scientists to rethink their search for life on Mars. The new evidence shows that life can thrive even among the harsh environments of early Earth.

"This discovery turns the study of planetary habitability on its head," said Vickie Bennett, a researcher with Australian National University. "Rather than speculating about potential early environments, for the first time we have rocks that we know record the conditions and environments that sustained early life. Our research will provide new insights into chemical cycles and rock-water-microbe interactions on a young planet."

Researchers detailed their discovery in the journal Nature.