Final answer:
Seafloor spreading is the process of forming new oceanic crust at mid-ocean ridges and pushing apart the existing crust. It starts with a rapid drop of the seafloor caused by the weight of mountains, creating a concave basin. Sediments like shales are deposited in this basin.
Step-by-step explanation:
The seafloor spreading process is a fundamental concept in geology that explains the movement of Earth's tectonic plates. It occurs at mid-ocean ridges where new oceanic crust is formed and pushes the existing crust apart. This process starts with a rapid drop of the seafloor caused by the weight of mountains, bending the lithosphere and creating a concave basin. Sediments such as shales are then deposited in this basin.