The Earth’s crust is thinnest beneath the oceanic regions, particularly at mid-ocean ridges where tectonic plates are diverging. In these areas, the crust can be as thin as 5 to 10 kilometers (3 to 6 miles) thick. This thinness occurs due to the processes of seafloor spreading, where molten material from the mantle rises to create new oceanic crust as the tectonic plates pull apart.
In contrast, the continental crust, which covers the landmasses, is generally much thicker, averaging around 30 to 50 kilometers (about 19 to 31 miles), and can be even thicker in mountainous regions. Overall, the oceanic crust’s relative thinness is a key feature of plate tectonics and contributes to the geological activity often associated with oceanic regions.