Abstract

The detection of life in extreme environments and the amazing capacity of microbes to obtain energy from the environment has led to the hypothesis that heat, not water or energy sources, is the final barrier that constrains life on Earth. As such, life is expected to extend far into Earth’s crust, potentially inhabiting an environment as extensive as the world’s oceans [1]. This chapter aims to summarize what is currently known about life in the oceanic crust, which contains all three domains of life and is a vastly underexplored habitat. This is not the first summary of this topic, and additional content can be found in numerous review and primary research papers [2–16], book chapters [17, 18], and books [19–21].