Why is Earth Missing a Huge Part of its Crust?

When the earth was totally covered in ice it is believed that a thief called Snowball Earth took away the crust.  Geo scientists believe that when the earth was covered in ice the glaciers while traveling eroded the layer of earth that is now missing.  Researchers suggest that about a 3 mile layer of earth was destroyed by these glaciers.

In the Grand Canyon you can see the layers of earth that were formed when the earth began.  The layers are the Cambrian Period that was around 540 million years ago where they left behind sedimentary rocks packed with fossils.  One of the other layers is one that was fossil-free crystalline basement rock that formed over a billion years ago.  There is a missing layer that is known as the Great Unconformity.