This award will support a three-year effort in the Caltech shock wave laboratory to measure properties of rocky and metallic liquids under conditions matching those in the deepest parts of the Earth. This information is critical to interpreting geophysical observations of the lower mantle and core in terms of composition, temperature, heat flow, and evolution over time. It also allows speculative ideas about an early molten earth to be developed into detailed theories. Shock compression is the only experimental method that can simultaneously measure density, pressure, temperature, energy, and sound speed of liquids at such extreme conditions.
The experimental and science agenda in this proposal is driven by key technical advances. Development of an encapsulation technique allowing us to pre-heat silicate glasses well above their melting point without formation of bubbles and in sealed behind a transparent window allows us to observe thermal radiation from the shocked liquid. Measurement of temperatures and sound speeds in shocked magmas will complete our ability to describe their properties at any desired pressure and temperature. Likewise, the development of graded density impactors for customized shock-and-ramp loading paths, together with our pre-heating capability and development of advanced window materials enabled measurement of the sound speeds and densities of liquid iron alloys along actual outer core temperature profiles. This novel experimental measurement will make the well-defined observed gradient in sound speed with depth in the outer core a new and critical constraint on outer core composition.
