Possible evidence of life on Earth at least 4.1 billion years ago

The scale bar on this image of a zircon crystal is roughly the width of a human hair. (credit: Geological Survey of Canada)

In 2008, a splashy paper hinted at evidence for life on Earth well over four billion years ago. Prior to these results, the oldest things we think were actual fossil microbes were about 3.4 billion years old, and the oldest (disputed) chemical signatures potentially left by life were about 3.8 billion years old. So the discovery was a pretty big deal. Unfortunately, though, that paper turned out to be a mistake—the samples had been contaminated during preparation.

Now, a new study from a different set of researchers presents a very similar splashy data—with contamination ruled out much more carefully. And that data at least opens the possibility that life was present at least 4.1 billion years ago. That would be incredible, considering that the planet itself is only a little over 4.5 billion years old.

Like the 2008 study, these researchers were examining the oldest pieces of the Earth we’ve found: tiny zircon crystals found in some rocks in Western Australia. The oldest of these crystals, which are remnants of granite that eroded away, date to almost 4.4 billion years ago. But some early sedimentary rocks ended up in the magma that turned into that granite, so there are interesting clues about the Earth's surface locked inside these zircons as well.

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