In 2012, scientists completed a first-ever study with detailed data on the limits of life that thrives deep in the cracks of hot undersea volcanoes, places called hydrothermal vents. The microbes that live in the ocean depths inhale hydrogen and carbon dioxide and exhale methane. There is a tremendous, enormous amount of microbial biomass living within the Earth’s crust in the sediments. Some estimates are that it’s about 1/3 of the total biomass. Others have suggested that it may even rival the biomass that’s living on the surface of the planet.
Astrobiologists think that if there is life in our solar system, say, on Mars, or on Europa, then it’s going to be similar kinds of life. Life that’s independent of sunlight and life that’s independent of oxygen. So by understanding the life and the constraints on the life that lives in these hydrothermal environments, it gives us some idea of what to expect we can expect on these other planets and how we might be able to model this life, using computer models.