What is the thickest layer of the earth?

The thickest layer of the Earth is the mantle. It lies between the Earth's dense, super-heated core and its thin outer layer, the crust. The mantle is primarily composed of silicate rocks that are rich in iron and magnesium. It is about 2,900 kilometers (1,802 miles) thick, making up roughly 84% of the Earth's total volume. The mantle isn't uniform; it is divided into the upper and lower mantle, based on changes in composition and physical properties.

The upper%20mantle is partially molten, specifically the asthenosphere, which allows the lithospheric plates (crust and uppermost mantle) to move. The lower%20mantle is more rigid due to immense pressure. Convection currents within the mantle drive plate tectonics, leading to earthquakes, volcanic activity, and the formation of mountains.