Geomicrobiology is when tiny living things, like bacteria, interact with rocks and minerals in the ground. Just like how we need food to survive, these tiny living things need minerals and other stuff in the ground to survive. They eat the minerals and break them down, changing the properties of the ground as they do it. This can have big effects on our earth, like changing the way water flows or creating underground caves. People who study geomicrobiology want to learn more about these tiny living things and how they interact with the world around them.