By analysing ancient minerals in western Australia, a team from the University of California identified signs of life inhabiting Earth around 4.1bn years ago – over 300m years earlier than other estimates, and only a short time after the planet first formed around 4.5bn years ago.
"Twenty years ago, this would have been heretical; finding evidence of life 3.8bn years ago was shocking," said Mark Harrison, co-author of the research, which is published in the journal Proceedings of the National Academy of Sciences.
Life on Earth may have started almost instantaneously. With the right ingredients, life seems to form very quickly.
The discovery throws our understanding of the earth's early years into confusion – it was thought that the planet was so dry and desolate during that time that life would have been impossible.
"The early Earth certainly wasn't a hellish, dry, boiling planet; we see absolutely no evidence for that," Harrison said. "The planet was probably much more like it is today than previously thought."
The minerals looked at were called zircons. Heavy and durable, these pieces of rock were first formed from magma billions of years ago, and have survived essentially unchanged. While solidifying, they captured and preserved whatever was in their immediate environment, and as a result they are like time capsules.
The team looked at 79 zircons in microscopic detail, and found that one contained tiny dark specks of graphite, which is pure carbon. Since carbon is the key building block of life, its presence revealed that life probably existed at the time of its formation.
Harrison said he was “very confident” that the zircon contained graphite that was 4.1bn years old.
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 non-biological origin into a zircon.