IGPP Seminar Series

Probing the Dark Age: Crust-Water Interactions on Hadean Earth

by Mark Harrison
IGPP, UCLA

Abstract

The Hadean Eon (4.5-4.0 Ga) is the dark age of Earth history; there is no known rock record from this period. However, detrital zircons as old as nearly 4.4 Ga from the Jack Hills, Western Australia, offer unprecedented insights into this formative phase of Earth history. Investigations using these ancient zircons reveal enrichments of heavy oxygen isotopes, fractionation of plutonium from uranium, inclusion assemblages characteristic of modern convergent margin magmas, and evidence of silicate differentiation at 4.5 Ga. These observations have been interpreted to reflect an early terrestrial hydrosphere, early felsic crust in which granites were produced under high water activity conditions, and even the existence of plate boundary interactions. This stands in strong contrast to the traditional view of an uninhabitable, hellish world. Possible scenarios are explored with a view to reconciling this growing but fragmentary record with our knowledge of conditions then extant in the inner solar system.
Tuesday, 14 October 2008
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM