Ancient rocks reveal how water helped shape the world

Published in Nature’s Communications Earth and Environment Journal, the research team studied 1.6-billion-year-old rocks from the Georgetown Inlier in northeast Queensland – home to some of the best-preserved pieces of continental crust on Earth.

According to ETH researcher Silvia Volante, who led the research at Curtin University's School of Earth and Planetary Sciences, the findings could redefine our understanding of the role water played in Earth's early evolution and its importance in shaping the continents as we know them.

“In the early days of our planet, volcanic rocks erupted on the ocean floor and were then altered by hot water as they cooled down and solidified. Over time, these water-rich rocks were buried deep within the Earth’s crust, where the introduction of additional water caused them to partially melt at temperatures ranging from 700 to 750°C,” Silvia Volante says. By analysing the oxygen levels within the rocks, the research team found a clear difference between the original volcanic rocks and the granitic rocks they turned into – suggesting an additional source of water from deep within the Earth’s mantle.

“The two sources of water which formed the continental crust rocks – one from the volcanic rocks themselves, and more surprisingly also from deep within the Earth – fuelled a chain reaction of melting which lasted millions of years and helped form the building blocks of the continents we live on today.”

The research team was fortunate to be able to study Australia’s ancient rocks, which offer a rare and well-preserved record of how the Earth formed. Co-author of the study, Li Zheng-Xiang said “We had an incredible opportunity to work in unique locations such as the Georgetown Inlier, which is one of the only places in the world where we can see all stages of continental crust formation locked in billion-year-old rock. Our next step is to investigate whether similar water-based melting processes occurred in even older crust fragments. Finding more well-preserved examples will help show just how crucial water movement in the Earth’s mantle was in shaping our planet’s early landscape.”