How water shaped Earth’s evolution three billion years ago

A recycling process between the Earth’s deep, scorching mantle and its surface water occurred some three billion years ago, generating magma-forming volcanoes that built continents, a new research paper has revealed. The phenomenon occurred much earlier than previously assumed, said geologists in a research paper published inNature Communications.

An international team of researchers studied the oldest volcanic rocks from Western Australia’s Pilbara Craton and found that water both shaped an infant Earth’s interior and catalysed volcanic activity. Water was transported deep into the Earth’s surface, the mantle, aiding the creation of magma that triggered volcanoes such as those in the contemporary the Pacific “Ring of Fire”.

“These rocks formed more than three billion years ago, when Earth was a very different place,” said lead author Eric Vandenburg, from the School of Physics, Chemistry and Earth Sciences, adding that the research provides a rare window into Earth’s distant past.

Water continues to be recycled through plate tectonics (where the Earth’s outer shell, or lithosphere, is torn into moving slabs of rock called “tectonic plates”) even today: oceanic water permeates into the mantle at subduction zones (where two tectonic plates collide and one slides beneath another), firing volcanoes.

“What surprised us was finding evidence that large amounts of water had already made their way deep into the Earth’s interior and influenced the formation of volcanic rocks,” said Dr. Vandenburg, in a release.

Through a phenomenon called “dripduction” water-saturated areas of Earth’s cool crust periodically seeped into the hot mantle, releasing water and creating magmas that lead to volcanic eruptions and the formation of rocks. “Dripduction locally recycled surface water and generated arc-like magmas… possibly promoting mantle-ocean-atmosphere volatile exchange during the Archean [the era when Earth’s crust cooled, oceans formed, and the earliest single-celled microbial life emerged around three billion years ago],” said the paper.

It added that dripduction is characterised by “poorly defined plate margins” that allow subduction, where a plate drips rather than sinks as a rigid slab.

“The Earth wasn’t operating exactly as it does now, but it appears some of the key processes were already in place,” Dr. Vandenburg said in a release. This discovery, that materials on Earth were exchanged between its surface and deep interior gives us clues about volcanic eruptions, continental formations, the evolution of the planet and the ingredients crucial to life on Earth.

Recycling lithospheric material into the mantle is a crucial process that shapes the chemical evolution of Earth and its habitability, the authors wrote in the paper.

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