Drop of Ancient Seawater Reveals Plate Tectonics Began 3.3 Billion Years Ago

A drop of ancient seawater that survived a trip through the Earth's mantle reveals that plate tectonics began hundreds of millions of years earlier than first thought.
John Loeffler

Plate tectonics, the essential and unique-to-Earth process that powers everything from volcanism to atmospheric conditions, was long thought to have begun around 2.7 billion years ago, but now a drop of ancient seawater reveals that the process began more than half a billion years earlier than we previously thought.

Plate Tectonics Began More than Half a Billion Years Earlier than Thought

The Earth is the only world in our solar system known to have plate tectonics, and this essential function of our planet is responsible for everything from volcanic activity to the formation of mountains to the conditions in our atmosphere. For as much as we know about this unique system of ours, when it all began is still up for debate and new evidence provided by a drop of ancient seawater reveals that this process began much earlier than we first realized.


In a new paper published in the journal Nature, an international team of researchers looked deep into our past to identify the microscopic remains of a drop of ancient seawater encapsulated in rock that formed on the Earth's surface, journeyed through the Earth's mantle, and reemerged on the surface through the tectonic process.

Ancient Seawater Rock
Source: A. Sobolev, E. Asafov, A. Gurenko, N. Arndt, V. Batanova, M. Portnyagin, D. Garbe-Schönberg, A. Wilson & G. Byerly/Nature


"Plate tectonics constantly recycles the planet's matter, and without it the planet would look like Mars," said Professor Allan Wilson from South Africa's University of the Witwatersrand (Wits) School of Geosciences, a member of the research team that identified the seawater deposit. "Our research showing that plate tectonics started 3.3 billion years ago now coincides with the period that life started on Earth. It tells us where the planet came from and how it evolved."

The Wits team examined a sample of komatiite that is a remnant of the hottest magma ever to exist and which was produced in the first billion or so years of the Earth's existence, known as the Archaean era. While this form of rock is normally weathered away when exposed on the surface, a small portion of this rock was contained in another mineral, called olivine, which preserved the ancient komatiite.

"We examined a piece of melt that was 10 microns (0.01mm) in diameter, and analysed its chemical indicators such as H2O content, chlorine and deuterium/hydrogen ratio, and found that Earth's recycling process started about 600 million years earlier than originally thought," Wilson said. "We found that seawater was transported deep into the mantle and then re-emerged through volcanic plumes from the core-mantle boundary."

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