Life on Earth may have sprung up "almost instantaneously" shortly after our planet formed some 4.5 billion years ago, some 300 million years earlier than previous studies have suggested, researchers say.
Geochemists at UCLA say the evidence is in tiny specks of graphite encapsulated in immensely old zircon crystals found in Western Australia.
Atoms in the particles of graphite, a crystalline form of carbon, bear hallmarks of biological origin, they say, and the zircon crystals have been dated to 4.1 billion years old.
"Twenty years ago, this would have been heretical; finding evidence of life 3.8 billion years ago was shocking," says professor of geochemistry Mark Harrison, one of the authors of a study appearing in the Proceedings of the National Academies of Science.
Life on Earth may have begun almost instantaneously, Harrison suggests.
Life seems capable of forming very quickly if the proper ingredients are available, he says.
If the zircon evidence holds up it could suggest that life already existed on Earth before the massive bombardment in the early solar system 3.9 billion years ago that left its mark in the craters that cover our moon, a bombardment that wouldn't have spared Earth.
"If all life on Earth died during this bombardment, which some scientists have argued, then life must have restarted quickly," says study co-author and graduate student Patrick Boehnke, working in Harrison's lab.
Rather than being a dry, desolate planet during that era, it may have resembled the Earth as it is today, the researchers say.
"The early Earth certainly wasn't a hellish, dry, boiling planet; we see absolutely no evidence for that," Harrison says.
In fact, it was possibly much more like the Earth is today than previously believed, he says.
For their study the research team, led by doctoral researcher Elizabeth Bell, looked at about 10,000 zircon crystals that formed out of molten magma being deposited in Australia.
Zircons, related to a synthetic material used to make imitation diamonds, are heavy and durable minerals that can capture and then preserve evidence of their immediate surroundings as they form, allowing scientists to use them as a sort of time capsule.
Spectrographic examination of 79 of the crystals found instances of graphite, a pure form of carbon, in several locations.
Are they confident about their findings?
"Very confident," says Harrison. "There is no better case of a primary inclusion in a mineral ever documented, and nobody has offered a plausible alternative explanation for graphite of nonbiological origin into a zircon."
In addition, the researchers say, the graphite/carbon in the crystals shows a characteristic chemical signature that not only suggests life was present but that it may have already developed the ability to photosynthesize.
"We need to think differently about the early Earth," says Bell.
