The Earth's crust isn't a uniform layer with a fixed depth. It varies considerably depending on whether you're talking about continental crust or oceanic crust.

Here's a breakdown:

* Continental Crust: This is the thicker of the two, ranging from about 30 to 70 kilometers (19 to 43 miles) in depth. It's composed of a variety of igneous, metamorphic, and sedimentary rocks.

* Oceanic Crust: This is thinner and denser, averaging about 7 to 10 kilometers (4 to 6 miles) in depth. It's primarily made up of basalt and gabbro.

Important Note: These are just averages. The actual depth of the crust can vary significantly depending on the location and geological history of the region.

It's also worth remembering that the crust sits on top of the mantle, which is a much thicker and denser layer of rock. The boundary between the crust and the mantle is called the Moho discontinuity.