What Is the Earliest Evidence for Life on Earth?
by Ross Pomeroy
For the first 600 million years of Earth’s 4.54 billion-year history, our planet was a hellish place. The rampant volcanism and frequent collisions that wracked our world rendered the surface unforgiving and purportedly inhospitable to life. While water was probably present, the oceans of the time may instead have been rolling seas of magma. The name for this period, the Hadean, is borrowed from Hades, the Greek god of the underworld. The moniker’s meaning is obvious: early Earth was a place of death.
Yet it was on this comparatively cursed landscape that –against all odds — life might have emerged. The controversial clue to this incredible notion was made public last fall. Scientists from UCLA showed off apparently biogenic carbon that was locked away inside a near impenetrable crystal for 4.1 billion years.
The oldest rocks on Earth don’t even date back that far, but peculiar minerals called zircons do. The oldest-known zircons, discovered in the Jack Hills of Western Australia, originally crystalized 4.4 billion years ago! It was within one of these zircons that geochemist Elizabeth Bell and her team discovered the carbon they think was produced by life. Life that old, whatever it was, would not have bones, or even a clearly-defined shape, so a true fossil find will probably never be unearthed. Instead, whatever carbon-based life existed back in the Hadean would simply leave traces of itself in the form of carbon itself. Bell’s co-author, Mark Harrison, referred to the stuff as “the gooey remains of biotic life.”