Scientists have found what they think is the oldest fossil on Earth, a remnant of life from 3.7 billion years ago when Earth’s skies were orange and its oceans green.

In a newly melted part of Greenland, Australian scientists found the leftover structure from a community of microbes that lived on an ancient seafloor, according to a study in Wednesday’s journal Nature .

The discovery shows life may have formed quicker and easier than once thought, about half a billion years after Earth formed. And that may also give hope for life forming elsewhere, such as Mars, said study co-author Martin VanKranendonk of the University of New South Wales and director of the Australian Center for Astrobiology.

“It gives us an idea how our planet evolved and how life gained a foothold,” VanKranendonk said.

Scientists had thought it would take at least half a billion years for life to form after the molten Earth started to cool a bit, but this shows it could have happened quicker, he said. That’s because the newly found fossil is far too complex to have developed soon after the planet’s first life forms, he said.

In an outcrop of rocks that used to be covered with ice and snow, which melted after an exceptionally warm spring, the Australian team found stromatolites, which are intricately layered microscopic layered structures that are often produced by a community of microbes. The stromatolites were about .4 to 1.6 inches high.

It “is like the house left behind made by the microbes,” Van- Kranendonk said.

“It would have been a very different world. It would have had black continents, a green ocean with orange skies,” he said.