Australasian Science: Australia's authority on science since 1938

Oldest Fossils Prove that Life Thrived on Young Earth

Australian researchers have uncovered the world’s oldest fossils in a remote area of Greenland, capturing the earliest history of the planet and demonstrating that life on Earth emerged rapidly in the planet’s early years.

Led by Prof Allen Nutman of The University of Wollongong, the team discovered 3.7-billion-year-old stromatolite fossils in the world’s oldest sedimentary rocks in the Isua Greenstone Belt along the edge of Greenland’s icecap.

Nutman said that the Isua stromatolite fossils were 220 million years older than the world’s previous oldest stromatolite fossils in Western Australia. This therefore pushes the fossil record back to just after the start of the Earth’s geological record, and points to evidence of life on Earth very early in its history.

The Isua stromatolites, which were exposed by the recent melting of a perennial snow patch, were laid down in shallow sea, so they provide the first evidence of an environment in which early life thrived.

Stromatolite fossils are mounds of carbonate constructed by communities of microbes. “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,” Nutman said. “This indicates that as long as 3.7 billion years ago microbial life was already diverse.”

Co-lead investigator A/Prof Vickie Bennett of The Australian National University said the study, published in Nature, provided a new perspective into the history of the Earth. “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,”she said. “Our research will provide new insights into chemical cycles and rock–water–microbe interactions on a young planet.”

Prof Martin Van Kranendonk of the Australian Centre for Astrobiology at The University of NSW said the discovery could point to similar life structures on Mars, which 3.7 billion years ago was a damp environment. “The structures and geochemistry from newly exposed outcrops in Greenland display all of the features used in younger rocks to argue for a biological origin,” he said.

“This discovery represents a new benchmark for the oldest preserved evidence of life on Earth. It points to a rapid emergence of life on Earth and supports the search for life in similarly ancient rocks on Mars.”