The thickest section of Earth is the mantle, which extends from about 30 kilometers (19 miles) below the Earth's surface to about 2,900 kilometers (1,800 miles). This makes it the thickest layer, accounting for about 84% of Earth's total volume.

While the Earth's crust is the outermost layer, it is much thinner compared to the mantle, with an average thickness of about 30 kilometers (19 miles).