Extensional tectonics is a branch of geology that focuses on the processes by which the Earth's crust is stretched and pulled apart. This can lead to the formation of rift valleys, grabens, and other features associated with the divergence of tectonic plates. Extensional tectonics is often associated with the formation of ocean basins and mid-ocean ridges, as well as with the breaking apart of continental landmasses. It is a key factor in the evolution of the Earth's lithosphere and plays a significant role in shaping the planet's surface and geological history.