Plate tectonics determines how the surface of the Earth is shaped over geological time; however, we do not know how this process started. New research by a group of geoscientists demonstrates that diamonds can be used to reveal how a buoyant section of mantle beneath some of the continents became thick enough to provide long term stability.
In this study, Smit et al. used sulfur isotopes in diamonds to show that atmospheric sulfur was entering the mantle 3 billion years ago through plate subduction. Older diamonds do not contain this element which indicates that plate tectonics started on Earth around 3 billion years ago.
Earth’s oldest continents are stabilized by thick lithospheric mantle keels. These mantle keels have different chemical and physical properties than the upper mantle, which isolate them from mantle convection. Models for the formation of these mantle keels range from horizontal tectonic processes such as stacking of subducted oceanic lithosphere to vertical tectonic processes such as tectonic underplating. Underplating is the accumulation of partial melts at the base of the crust where an ocean plate is being subducted under continental crust. These divergent models have led to debate between proponents of horizontal versus vertical processes in the formation of the earliest continental lithosphere.
https://science.sciencemag.org/content/364/6438/383
https://phys.org/news/2019-04-diamonds-reveal-continents-stabilized-key.html