The average thickness of the earth's crust is about miles.

The average thickness of the earth's crust is about 18 miles under the continent and 3 miles under the ocean.

Explanation:

Crust is defined as the outermost shell which is solid in every planet and natural satellite. Crust is formed above the mantle.

The crust is composed of different chemicals and generally formed by igneous process and modified later by environmental hazards like soil erosion, eruption of volcano, sedimentation caused during floods etc.  

Generally, the crust of in a planet tend to be uniform in composition, properties and also thickness.

But in Earth crust is of two types. Because the crust formed in the land or say below the continents have different compositions and physio-chemical properties compared to the crust formed below oceans.

So the crust in earth is classified in two types. They are continental crust and oceanic crust.

Even the formation of continental and oceanic crust differs from each other because the solid outermost shell of the continents are harder than the outermost solid shell of the oceans.

So the thickness of the continental crust is about 18 miles and oceanic crust is about 3 miles only. Thus the continental crust is thicker and harder than oceanic crust.

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia