The Pd-Ag chronometer: accretion, early planetary differentiation and the loss of volatil…

In this talk, I will discuss the application of the Pd-Ag decay system to study (i) the timing of volatile element depletion in carbonaceous chondrites, (ii) the crystallization history of iron meteorites, which are thought to represent samples from small asteroidal cores and (iii) accretion models of the Earth; in order to better constrain the history of moderately volatile elements in our solar system.
For example, the Earth’s mantle is similar in Ag isotope composition to primitive, volatile-rich CI chondrites. This implies that the Earth accreted a significant amount of material with high contents of moderately volatile elements. Contradictory evidence from chromium and strontium isotopes exists and can be reconciled by heterogeneous accretion. This encompasses the early accretion of dominantly volatile-depleted material followed by volatile-rich material with possibly high water content. The model also indicates that the Moon-forming giant impact involved the collision with a Mars-like protoplanet, enriched in moderately volatile elements.