Special Seminar: Janne Blichert-Toft

"Deep Time: What isotope geochemistry has taught us about Earth’s early evolution"

Abstract:  I will review some of what isotope geochemistry has taught us about Earth’s evolution, especially the earliest parts of it, which we often refer to as Deep Time. I will aim at doing this in as general terms as possible so as to make the seminar accessible to non-isotope geochemists. Since we cannot discuss the Earth without also discussing the Moon, the Giant Lunar Impact will be part of the talk. I will in chronological order go through those major milestones of Earth’s evolution that have been forged so far with the help of long-lived and extinct radioactivities. The data I will show to tell the early history of our planet will be mostly my own and those of our students. The most important milestones include the age of the Solar System (Time Zero) and, hence, the age of the Earth short of being able to date the Earth directly, the age of terrestrial core formation, the age of the Giant Lunar Impact, the age of the Late Veneer, the existence of a terrestrial magma ocean, a concept that has been repeatedly in and out of vogue, the age and nature of the earliest proto-crust, the age of the first continents, and the time of onset of plate tectonics, the latter obviously speculation only. If time permits, I will briefly discuss the existence and whereabouts of the so-called “Hidden Reservoir” from the perspective of the refractory lithophile long-lived isotope systems.

Janne Blichert-Toft, Directeur de Recherche CNRS
Ecole Normale Supérieure de Lyon, Laboratoire de Sciences de la Terre, Lyon, France