Here's a breakdown of Earth's layers and their relative thicknesses:

* Crust: The thinnest layer, ranging from about 3-5 miles (5-8 km) thick under the oceans (oceanic crust) to about 25 miles (40 km) thick under the continents (continental crust).

* Upper Mantle: Includes the lithosphere (rigid, outermost part of the mantle, including the crust) and the asthenosphere (a partially molten, relatively weak zone). The lithosphere is about 60 miles (100 km) thick, while the asthenosphere extends down to about 410 miles (660 km).

* Lower Mantle: The thickest layer, extending from 410 miles (660 km) to 1,800 miles (2,900 km).

* Outer Core: A liquid layer about 1,400 miles (2,200 km) thick.

* Inner Core: A solid ball of iron and nickel about 750 miles (1,220 km) in radius.

Therefore, the crust is the thinnest layer, and the asthenosphere is a part of the upper mantle, which is significantly thicker than the crust.