Definition: The Earth is separated into four major strands: the exterior solid crust, the mantle, the outer core, as well as the inner core.
The crust seems to be the thinnest earth's layer accounting for much less than 1% of its total volume."
The crust's typical thickness is approximately 40 kilometers. This is further subdivided into fifteen main tectonic plates. Such plates have such a hard center point, although geological activity such as volcanism can occur along the edges.
Therefore, the earth's thinnest layer is the crust.