NASA Astrobiology Institute (NAI)

This project is designed to provide information on the origin of Earth’s water. Comparing the isotopic composition of Earth’s primordial water (D/H ratio) with the ratios of other solar system objects can help to constrain possible sources of the water. The current ocean, other surface waters, and water in the upper mantle have experiences 4.5 billion years of geologic processing that has changed the original isotopic composition. By concentrating on rapidly quenched, under-gassed lavas from hot spots like Hawaii and Iceland, we hope to identify water that has not been through the extensive processing experienced by the surface water. Such a reservoir may have survived unaltered since shortly after the accretion of the Earth and thus may provide a better idea of the original composition of the Earth’s water.

During the past year, we have acquired a suite of samples from the Hawaii deep drill core that were erupted under the ocean at a depth where gases are retained in the lava by the pressure of the overlying water. We have begun to prepare these samples for study. Each sample is being cut into thin slices. Both sides of the slices are polished to provide as much surface area as possible. The polished sections will be examined by petrographic microscope and SEM to identify melt inclusions within olivine phenocrysts that hopefully trap hydrogen from the magma before the water in the magma mixed extensively with surface waters. These melt inclusions will be measured, along with some glass from around the olivine grains, with the Cameca ims 1280 ion microprobe in the W. M. Keck Cosmochemistry laboratory at the University of Hawaii to determine the D/H ratio of the water. Dr. Binsted is doing most of this work.

Dr. Meech took a trip to Iceland to gather samples.

In preparation for the ion probe measurements, we have obtained, with the help of Rhea Workman of UH, a suite of volcanic glasses with known hydrogen contents and D/H ratios to use as standards. We have made some special mounts for the standards. Within the next few weeks the standards will be mounted and characterized in the ion probe.