Resumen de Impacts from space started Earth's tectonics
Nicolas Greber of the University of Geneva, Switzerland, and his colleagues set out to trace the origin of global plate tectonics by determining which rock types were present at different stages of Earth's history. They focused on two rock types. Mafic rocks like basalt are typically dark, while felsic rocks like granite are lighter. Greber determined how early in Earth's history felsic rocks were present by looking at shales dating back 3.5 billion years. Mafic and felsic rocks carry different mixtures of titanium isotopes, which are preserved in the shales. This revealed that, as far back as 3.5 billion years ago, 55 to 60 per cent of the continental crust was made of felsic rocks.
