EARTH × ATMOSPHERE

The Oceans Came Early

~4.4 billion years ago

Hadean

Grains of zircon from Western Australia are the oldest solid pieces of the Earth we possess, older than any rock that survives. The molten rock they grew in had swallowed older material, altered beforehand by liquid water at low temperature, and the crystals still carry that signature in their oxygen. Read at face value, that signature puts liquid water, perhaps oceans, at the surface within 150 million years of the planet's formation.

Why it matters

The Earth's opening chapter is usually painted as a field of lava. These crystals argue instead for a world of rain, of water, perhaps of seas, almost from the start; and every million years taken off the hellish era is another million in which life could have begun.

Dating & uncertainty

Each grain is a loose crystal, washed out of its parent rock and buried in one far younger, so it dates its own crystallisation and nothing else. And reading its oxygen as the mark of cool surface water remains an inference: nothing of that surface survives to check it against.

Sources

1. Wilde et al. (2001), Nature · Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago
2. Mojzsis et al. (2001), Nature · Oxygen-isotope evidence from ancient zircons for liquid water at the Earth's surface 4,300 Myr ago
3. Harrison (2009), Annual Review of Earth and Planetary Sciences · The Hadean crust: evidence from >4 Ga zircons

Earth history as one day

00:44:2423 h 16 min before midnight

if Earth’s 4.54 billion years were compressed into a single day