Studies of Earth's deep biosphere over the past few decades have shown that remarkable varieties of environments previously thought to be uninhabitable actually harbor significant quantities and a great diversity of microbial life. It has become apparent that many of the microorganisms living below the Earth's surface rely on geochemical reactions rather than photosynthesis as metabolic energy sources. Because of similarities in geochemical processes that are likely occurring, there are other examples of celestial bodies in our solar system that may also harbor subsurface biospheres, most notably Mars and the jovian moon, Europa. We can use lessons learned through investigations of Earth's deep biosphere to assess the possibility that life may exist below the surface of these worlds.

One of the major tools at our disposal for making these comparisons is geochemical modeling; such models are used to investigate the biogeochemical reactions that are likely to yield energy as water reacts with rocks and as fluids far from equilibrium with one another (e.g. vent fluid and seawater) mix together. In order to construct these models, we take advantage of the vast database available of the composition of host rocks and vent fluids from a variety of hydrothermal systems from the more silicic and acidic fluids found at Lau to the very reducing, high pH environments of Lost City. As such, these models represent one of the best methods for integrating and synthesizing the efforts of mid-ocean ridge researchers and expanding the impact of the Ridge program into the field of astrobiology.

During this meeting, I hope to discuss some of what we know about Earth's deep biosphere in the context of what it may tell us about the nature of life in similar environments outside of Earth. As plans are made for missions to search for deep biospheres on other worlds, we also explore what may be the most appropriate analogs here on Earth and how the methods being developed to study Earth's deep biosphere may aid in our search.