Planetary sciences

The formation of planets, in particular the Earth and the Moon, through the process of accretion and proto-planetary impacts, controls their chemical state and thus their present dynamics. The understanding of the emergence of planets from the pristine solar disk, relies on detailed observations of remote solar systems with different degrees of maturation, in particular the observation of exoplanets, and on high resolution isotopic measurements of the composition of chondrites, the initial building blocks of planets. This is where the world views and approaches of the astro- and geo-sciences meet.

The accretion of the Earth forming objects, the Moon-forming impact, the nature and duration of a magma ocean, the formation of the Earth’s core, the appearance of the Earth’s magnetic field, early mantle convection and the emergence of the first oceans, atmosphere and continental fragments, the effect of the late heavy bombardment, the emergence of life, the growth of the inner core, the birth of plate tectonics are all key events in the history of the young Earth occurring in the first one or two billions of years, which have left precious few traces that modern geosciences are increasingly able to uncover and unravel. The early history of the Earth has not been a “long quiet river flowing” (as the title of a famous French movie goes) but it has been punctuated by catastrophic events separating periods when the rules of the game may have changed, with the emergence of new media and structures after each revolution. This new view of a non-linear evolution with “phase changes” is in line with progress in non-linear physics and chaos theory. There were a “before” and an “after”, with often very different characteristics, regarding the appearance of many of the features recalled above.