In search of lost continents, and some really basic questions about the early Earth

Séminaire de Jun Korenaga (Professeur à Yale, USA)

The Hadean is the time when Earth is expected to have gone through the most drastic changes in Earth history, i.e., the formation of a magma ocean and its solidification, the appearance of oceans, and the transition from a massive CO2-rich atmosphere to a more moderate one. These events during the Hadean are responsible for the making of a habitable planet and set the stage for its subsequent evolution. However, it is also the most nebulous time with no direct rock record, and there are a number of fundamental questions yet to be answered such as whether plate tectonics already initiated and whether there was any continental crust in the Hadean. In this talk, I focus on one simple question, was there land on the early Earth, which has profound implications for the origins of life on Earth. Trying to answer this question leads us to critically examine the various aspects of the Earth system, including continental growth, the thermal evolution of oceanic lithosphere, the physics of plate tectonics, deep water cycle, and magma ocean solidification, and some of these topics will be discussed in detail.