3.8 billion years ago. That’s the widely accepted number for when life began on Earth. A UCLA-led team of scientists now contend that life began even earlier – at least 4.1 billion years ago.
Mark Harrison, a co-author of the study published in PNAS and a professor of geochemistry at UCLA, explains the significance of these findings. “Life on Earth may have started almost instantaneously,” said Harrison. “With the right ingredients, life seems to form very quickly.”
Wasn’t early Earth a hellish, hot place? Not so says Harrison. “The early Earth certainly wasn’t a hellish, dry, boiling planet; we see absolutely no evidence for that.”
Harrison adds, “the planet was probably much more like it is today than previously thought.”
Mark Harrison at UCLA. Credit: UCLA
The new date for when life started puts it before the immense bombardment responsible for the moon’s cratered appearance. Did life make it through this bombardment? Even if all life died, it “must have restarted quickly,” said Patrick Boehnke, another co-author of the study.
The answer lies in zircons
Zircons are heavy, long-lasting minerals that form from molten rocks. What makes them special is they preserve their immediate environment. The researchers studied more than 10,000 zircons for their study. 656 of them contained curious dark specks. Of these, 79 of them were studied using Raman spectroscopy. This is a technique that shows the molecular and chemical structure of ancient microorganisms in 3D.
In one zircon, the researchers found graphite (pure carbon) in two locations.
“The first time that the graphite ever got exposed in the last 4.1 billion years is when Beth Ann and Patrick made the measurements this year,” Harrison said.
Ok, so where does the 4.1 billion years ago date come from? The researchers know the zircon is 4.1 billion years old because of its ratio of uranium to lead. They don’t know exactly how old the graphite is, but they do know it’s older than zircon containing it.
Remember zircon is like a snapshot in time. When it forms, whatever is found within it is at least as old as the zircon.
Now, why does this graphite mean life? According to the researchers, it has a particular ratio of carbon-12 to carbon-13 indicating the existence of photosynthetic life.
“We need to think differently about the early Earth,” said Elizabeth Bell, lead-author of the study.
The implications of this discovery could be major. It suggests simple life on Earth formed very quickly. If simple life formed this fast on Earth, could life have formed on other terrestrial planets and bodies? That’s what these new findings suggest according to Harrison.