MATTER AT EXTREMES

22 ESRF

Earth, for example, exceeds that of the surface by at least one order of magnitude, implying that there may be the equivalent of several oceans of water trapped at depth. It is well established that even minor amounts of water at depth have a major impact on Earth s interior dynamics (generation of melts and convection), thus being essential for plate tectonics but also in triggering catastrophic events (explosive volcanic eruptions and deep earthquakes). Knowledge of volatile abundances at depth is therefore critical to understand deep planetary interior processes.

The deep volatile storage scenario remains, however, subject to debates due to the very few natural geological samples capable of

recording early stages of Earth formation and the experimental difficulties to study volatiles at these extreme conditions. In the early stages of Earth s history, the planet was likely entirely molten (magmatic ocean period) [2]. The magma ocean, initially rather homogenous in composition, de-mixed after ~ 20-60 Myrs into a metallic core and a silicate mantle due to gravitational forces [3]. Concomitant to this process, volatiles degassed from the magma surface to form the early atmosphere and the silicate mantle solidified upon cooling (Figure 9).

Disentangling the behaviour of volatiles during these complex processes remains very challenging. A new experimental approach was

Fig. 9: Schematic view of Earth s formation history

delineating three important stages: the magma ocean

period (left); core formation (centre, note the descending

metallic melt droplets) and mantle solidification, i.e., the

present state of the Earth, which is ~4.54 Gyrs old. Blue circles

represent volatile elements.

Fig. 10: Overview of the experimental approach (left), results obtained

(centre) and the derived implications for the distribution of krypton in the

lower mantle (right).