How Old is Life?

On the one hand, experiments tell us that the gap between non-living and living matter is even wider than naïve observation would lead us to believe.  The origin of life seems to require vast amounts of space and time and astronomically good luck.  On the other hand, life appeared on the primeval, Hadean Earth pretty much as soon as the Earth was cool enough that it wouldn’t be cooked.  In this latest fossil discovery, there was not just life but complex, multi-celled life at a time when Earth was still in its Hadean age.

A sliver of a nearly 3.5-billion-year-old rock from the Apex Chert deposit in Western Australia (top). An example of one of the microfossils discovered in a sample of rock from the Apex Chert (bottom).

As that story goes, in the half-billion years after it formed, Earth was hellish and hot. The infant world would have been rent by volcanism and bombarded by other planetary crumbs, making for an environment so horrible, and so inhospitable to life, that the geologic era is named the Hadean, for the Greek underworld. Not until a particularly violent asteroid barrage ended some 3.8 billion years ago could life have evolved.

But this story is increasingly under fire.  Many geologists now think Earth may have been tepid and watery from the outset. The oldest rocks in the record suggest parts of the planet’s crust had cooled and solidified by 4.4 billion years ago. Oxygen in those ancient rocks suggest the planet had water as far back as 4.3 billion years ago. And instead of an epochal, final bombardment, meteorite strikes might have slowly tapered off as the solar system settled into its current configuration.

Rebecca Boyle writes for Quanta Magazine

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