Processes in Earth’s lower mantle govern our planet’s inner dynamics and control surface plate tectonics. As such, a quantitative understanding of the physical and chemical properties of the lower mantle is pivotal to model Earth’s dynamic evolution, including the long-term chemical interactions between mantle and atmosphere that are vital to the development of habitability on Earth, and possibly other planets.

While seismic tomography is providing increasingly detailed three-dimensional maps of the lower mantle, the interpretation of tomographic models to elucidate key factors such as mantle geochemical heterogeneity or dynamic mantle flow processes has proven to be highly ambiguous.

All evidence points to phase transitions being the missing link needed to converge to a consistent interpretation of seismic observations. The same phase transitions also play a key role in governing mantle dynamics. But even fundamental properties, such as the location of major phase transition boundaries in Earth’s mantle, are poorly constrained. This is because the parameter space (pressure-temperature-composition) is huge and experimental measurements at planetary interior conditions are extremely slow.

DEEP-MAPS will employ a novel class of time-resolved high-pressure/-temperature experiments that reduce by several orders of magnitude the time for key experiments. This will allow DEEP-MAPS to map lower mantle phase transitions, their impact on physical properties and their seismic signature with practically continuous coverage in relevant pressure-temperature-composition-space. DEEP-MAPS will further probe the time-dependence of phase transitions, transforming our understanding of how to scale from laboratory measurements to geophysical processes.

DEEP-MAPS will provide a step-change in our ability to interpret mantle seismic observables and to quantify the geodynamic impact of mantle phase transitions, ultimately leading to a holistic picture of Earth’s deep mantle.