12: Impacts to the Lithosphere

Plate tectonics and the hydrologic cycle are well-recognized drivers of Earth’s rock cycle, but contributions from microorganisms and other life forms are also significant (Fig. \(12.1\)). Microorganisms push mineral weathering forward and thus help accelerate the transformation of rocks into sediments. Microbial reactions produce directly or indirectly many of the minerals that accumulate in depositional environments, some of which would not form in purely inorganic systems. Microbial reactions help convert sediments to sedimentary rocks during diagenesis. Moreover, by helping to drive weathering and determine the properties of sedimentary rocks, microorganisms even influence tectonic activity. Thus, microorganisms impact the lithosphere, the solid outermost rocky shell of the Earth, in diverse and significant ways.

In this chapter, we will consider these impacts in more detail. We will examine some of the major groups of microbial biominerals and the roles microorganisms play in forming them. We discuss how microbial activity affects the composition of sediments that are deposited in the oceans. We will also discuss how microbial activities have affected tectonic activity and the evolution of Earth’s mineralogy over time.

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