This reaction encapsulates key take-home messages of the field observations and laboratory dissolution experiments. water + rock + (acid or base)  chemicals in solution + precipitated solids reactants  products cations and anions (these include the nutrients for microbes) e.g., clays (these provide a long-term record of the presence of water)

We assess the habitability of Mars-like environments on Earth as “practice” for rover missions to Mars. We identify the requirements for life at these sites, such as the hydrothermal system at Lassen. We begin by first looking for the presence of liquid water, and then we identify the other requirements, and any solid minerals or rocks that formed in this system. 1. Liquid water 2. Source of energy - photosynthesis (light energy - chemosynthesis (chemical energy utilizing gases such as hydrogen and hydrogen sulfide from the magma) 3. Nutrients - Carbon (carbon dioxide gas from the magma) - Trace nutrients (elements dissolved into solution* from the rocks) *Clays can be formed as a solid product of water and acid/base reacting with a rock. They always form in the presence of water, and are very good at preserving organic material from dead/fossilized microbes. On Mars, the liquid water is now gone and all that’s left behind are the solid minerals and rocks. We have to read the story left behind in these solids in order to assess the habitability of a site. While on Earth we begin by first looking for liquid water, on Mars we begin by first looking for minerals or rocks that formed in the presence of liquid water. So we start with the solid and work our way back to the original liquid environment that it formed in. Young Mars several billion years ago Young Mars several billion years ago Present day Mars 1. Clays – these minerals require the presence of liquid water to form. Clays = liquid water. 2. Source of energy - For example, chemosynthesis (chemical energy) can be supported by the presence of other minerals containing sulfur, which may indicate that sulfide was present. 3. Nutrients - The presence of carbon and trace elements can be indicated by other minerals. *We read the story in the solids to infer the nature of an ancient environment that provided liquid water, energy, and nutrients. Earth studies guide Mars exploration

This reaction encapsulates key take-home messages of the field observations and laboratory dissolution experiments. On Earth we go to places with liquid water, and then characterize all of the processes that can make them habitable. On Mars we go to places with clays, and then determine whether other requirements for supporting life were once present. cations and anions (these include the nutrients for microbes) e.g., clays (these provide a long-term record of the presence of water) reactants  products water + rock + (acid or base)  chemicals in solution + precipitated solids