Ancient Earth's Volcanoes Were Already Fueled by Water 3 Billion Years Ago

Geologists studying some of Earth's oldest volcanic rocks have found evidence that water was already shaping the planet's interior and helping to drive volcanic activity more than three billion years ago. The findings, published in Nature Communications, come from an international team led by Adelaide University geochemist Dr. Eric Vandenburg.

The team examined ancient rocks from the Pilbara Craton in Western Australia, one of the best-preserved records of the early Earth. Their analysis suggests that water travelled deep beneath the surface before contributing to the formation of magma that fed volcanoes resembling those found today around the Pacific "Ring of Fire."

Today, plate tectonics carries water from the oceans down into the mantle at subduction zones, where one tectonic plate sinks beneath another; that water helps generate the magma that builds continents. But the early Earth was too hot for plates to move that way, so it had been unclear whether -- and how -- surface water could have reached the mantle so long ago. The researchers propose a different mechanism, which they call "dripduction": dense, water-rich sections of the planet's cooler outer crust periodically sagged and collapsed into the hotter mantle below, carrying their water with them and releasing it to help form magma that later erupted as volcanoes.

"These rocks formed more than three billion years ago, when Earth was a very different place," Dr. Vandenburg said. "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." He added that while the planet did not operate exactly as it does now, some of the key processes were already in place.

The study, which also involved researchers from Monash University, the Geological Survey of Western Australia, Curtin University, the Australian National University, Cardiff University and the GEOMAR Helmholtz Center for Ocean Research in Germany, reconstructed geological events from chemical signatures in rocks dated to roughly 3.1 billion years ago.