Final answer:
Finding a new mid-ocean ridge forming along an underwater mountain ridge suggests seafloor spreading and supports the theory of plate tectonics.
Step-by-step explanation:
When scientists find a new mid-ocean ridge forming along an underwater mountain ridge, it indicates the process of seafloor spreading. Seafloor spreading occurs when magma rises to the surface and creates new oceanic crust. This finding allows scientists to assume that tectonic plate movement is happening in that area, and it supports the theory of plate tectonics, which explains the movement and interaction of Earth's lithosphere.
Learn more about Seafloor spreading and plate tectonics