Water is one of the key ingredients for the habitability of the Earth. While 70% of the Earth?s surface is covered with water, far more water may exist in the rocks of the interior. This ?deep water? is believed to have been contributing to the evolution of the atmosphere and hydrosphere over geologic time scales. However, it is difficult to obtain samples from depths greater than ~10 km because of technological limitations. Therefore, it is important to conduct laboratory experiments on the main minerals at the high pressure-temperature conditions of the Earth?s interior. Laboratory experiments for the past two decades have shown that some minerals in the mantle above 660-km depth can contain large amounts of water, contributing to approximately one ocean mass of water stored in this part of the mantle. However, laboratory measurements have also shown that water storage capacities of some main minerals stable at the mantle from 660 km to 2900 km depths could be very low, leading to a hypothesis that the layer is essentially dry. However, the water storage capacity of the third most abundant phase in the lower part of the mantle, Ca(Ti,Si)O3 perovskite, has not been well studied. In this research project, researchers will synthesize Ca(Ti,Si)O3 perovskite at the high pressure-temperature conditions of the lower mantle and measure its water storage capacity. The measurements will advance our knowledge on how much water can be stored in the lower mantle, which represents more than 50% of the Earth?s volume. The researchers will also measure the impact of water solubility on the physical properties of Ca(Ti,Si)O3 perovskite, providing key data for investigating possible existence of water-rich regions in the lower mantle through seismic imaging methods. A Ph.D. student and undergraduate students will be trained for a comprehensive skill-set in high-pressure apparatus and in the characterization of very small run products. Informing the public about the important role of hydrogen in the interior of Earth (and other planets) will be achieved using the annual ?Earth and Space Exploration Day? open house and the campus-wide ?Night of the Open Door? event. The data analysis will be written in Jupyter notebook files and then converted to education materials for mineralogy and geochemistry courses at ASU.
Through this grant, PI Shim?s research group will measure the water storage capacity of Ca(Ti,Si)O3 perovskite. They will synthesize high-quality samples at the pressure?temperature conditions for the stability of Ca(Ti,Si)O3 perovskite in the large-volume press. The synthesized samples will be carefully analyzed using a range of techniques (infrared and Raman spectroscopy, thermogravimetric analysis, secondary ion mass spectrometry, X-ray diffraction, and electron microscopy) for possible H2O storage. The synthesized samples will also be studied in the diamond-anvil cell to measure the effects of H2O and Ti on the thermoelastic properties at mantle-related pressures. Intense effort has been made in Earth science over a decade to understand the role of the interior for the evolution of Earth?s atmosphere and hydrosphere. Yet, water storage in the lower mantle still remains uncertain. By studying the third most abundant mineral phase in the lower mantle, the research project will advance our knowledge on the deep H2O storage which is important for a range of issues in Earth science, including volatiles recycling, Earth formation and differentiation, and seismic structures in the deep mantle.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
