Today, the Earth’s surface is made up of continental and oceanic crust. Continental crust makes up the land we live on, and oceanic crust makes up the ocean floors.
These crusts can collide, often causing the heavier, denser oceanic crust to get thrust down under the continental crust. As it is thrust down into the earth, the oceanic crust takes ocean water with it. Eventually, the heat and pressure causes this oceanic crust to melt and combine with the water, forming a lighter weight magma which eventually will rise and cool to form new continental crust.
For a long time, it was assumed that this same process of water being dragged deep underground from the surface was what generated earth’s first continents. New research, by a team lead by Dr Robert Hugh Smithies of the Geological Survey of Western Australia and Curtin University, points to another explanation.
The team studied tiny crystals, called zircons, collected from some of earths earliest continental crust located in the Pilbara, Western Australia. Compositional analysis at Microscopy Australia’s University of Western Australia facility of these zircons allowed the researchers to determine both the origin of the water that formed them and the date at which they were formed.
What they uncovered was that this early continental crust did not form from surface water as It does today, but instead from primordial water, that already existed deep within the earth. This implies that the earth contained far more primordial water than previously thought and could have implications for how scientists think about how our planet, and early life, formed. It also challenges one of the central tenants of physical sciences: uniformitarianism, or the idea that physical processes in the present reflect the physical processes of the past.