Figure 11.25Sedimentary rocks recently discovered on Mars contain a variety of sulfate minerals that form by precipitation from water. The presence of jarosite shows that the waters from which they precipitated were extremely acidic. Extremophiles can live in these conditions, but it is not yet clear whether they could originate in such acidic waters. The holes in the rocks were drilled in 2004 by Opportunity, one of the Mars Exploration Rovers, to analyze their composition.