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Geologists studying some of Earth’s oldest volcanic rocks have discovered evidence that water was influencing the planet’s deep interior and helping fuel volcanic activity more than 3 billion years ago.
An international research team led by University of Adelaide geochemist Dr Eric Vandenberg analyzed ancient rocks from Western Australia’s Pilbara Craton. Their findings suggest that water was transported deep beneath Earth’s surface before contributing to magma formation and volcanic activity resembling processes associated with the modern Pacific Ring of Fire.
Published in Nature Communications, the study indicates that Earth may have been recycling water between its surface and interior much earlier than previously believed, despite the young planet operating very differently from Earth today.
New clues about the early Earth
Dr Vandenberg, from the University of Adelaide’s School of Physics, Chemistry and Earth Sciences, said ancient rocks provide a rare opportunity to study geological conditions from billions of years ago.
“These rocks were formed more than 3 billion years ago, when Earth was a very different place,” he said.
Today, plate tectonics helps transport water into Earth’s interior. At subduction zones, one tectonic plate sinks beneath another, carrying water from the ocean into the mantle. The water lowers the melting point of mantle rocks, helping generate magma that can rise toward the surface and contribute to volcanic and continental growth.
However, scientists have questioned whether similar water transport occurred more than 3 billion years ago, when Earth was likely too hot for modern-style plate tectonics.
“The early Earth was too hot for plates to behave that way, so it was unknown until now whether surface water was able to move into the deep interior more than 3 billion years ago, and if so, how,” Vandenberg said.
“What surprised us was finding evidence that large amounts of water had already reached deep into Earth’s interior and were influencing the formation of volcanic rocks.”
A geological process called dripping
The researchers propose that water may have entered the mantle through a geological process known as “dripping.” This mechanism could have operated before modern plate tectonics became established.
In this process, dense, water-rich sections of Earth’s cooler outer crust gradually drooped downward and collapsed into the hotter mantle. As the material descended, it released water into the mantle, where the water helped generate magma.
The magma eventually rose, erupted through volcanoes, cooled into rock, and preserved chemical evidence of these events for billions of years.
“Although the Earth did not function exactly as it does today, it appears that some of the key processes were already in place,” Vandenberg said.
When did Earth begin recycling surface materials?
The discovery addresses a major question in geology: How early did materials begin moving between Earth’s surface and deep interior?
Determining when water first began traveling deep underground is important because this recycling process influences volcanic activity, continental growth, and the movement of chemical elements essential for life.
The findings may also help scientists understand how Earth’s continents formed and how the planet gradually developed into its modern geological system.
Chemical evidence from 3.1 billion years ago
The Pilbara Craton is one of the world’s most valuable locations for studying the early Earth. Its exceptionally well-preserved rocks provide a rare geological record dating back billions of years.
By examining chemical signatures preserved within these ancient rocks, researchers reconstructed geological processes that occurred approximately 3.1 billion years ago.
The results suggest that Earth’s surface and deep interior were interacting far earlier than previously recognized. Rather than being relatively static, the young planet appears to have been geologically dynamic and already recycling one of its most important substances: water.
The study involved researchers from the University of Adelaide, Monash University, the Geological Survey of Western Australia, Curtin University, the Australian National University, Cardiff University, and Germany’s GEOMAR Helmholtz Centre for Ocean Research.
Source: www.sciencedaily.com