Exploring the deep Earth and planetary interiors by high-pressure experiments

While the deep Earth is not directly accessible, it can be explored by laboratory experiments under high-pressure and -temperature (P-T) combined with geophysical observations and geodynamical modeling. We conduct experiments using a laser-heated diamond-anvil cell (DAC) which can generate static high P-T beyond conditions at the center of the Earth. Combining such DAC experiments with in-situ X-ray observations at synchrotron sources and thermal/electrical conductivity measurements and ex-situ textural and chemical characterizations of recovered samples, we have been trying to uncover the structures, chemical compositions, physical properties, dynamics, and evolution of the deep Earth and planetary interiors. The lowermost part of the Earth’s mantle, sometimes called the D” layer, have been the most enigmatic region inside our planet, but the discovery of its main constituent crystals of post-perovskite dramatically improved our understanding of this mysterious layer. Recent hot debates on the core include its thermal conductivity and the mechanism of its convection that have sustained the planetary magnetic field since early history of the Earth. In addition, the Earth’s core is known to include substantial amounts of light elements such as sulfur, silicon, oxygen, carbon, and hydrogen, but its exact chemical composition has been highly controversial since Birch (1952). Hydrogen could be one of the important core light elements when considering that a large amount of water may have been delivered to the growing Earth and hydrogen is strongly siderophile (iron-loving) under high pressure. Nevertheless, the phase diagram and properties of iron hydrides are little known since hydrogen is least soluble into iron at ambient conditions. I will introduce these high-pressure studies on the deep mantle and core materials including our recent work on iron hydrides and discuss the possible ranges of Earth’s core composition.