Answer: The plates are able to shift and flex because the float on a soft layer called asthenosphere.
Explanation:
Asthenosphere is the layer of the Earth's mantle that is below the lithosphere.
It is a ductile and weak part of the Earth that is about 180km thick.
It is the layer of solid rock that is been pressurized and heat the rocks can flow like a fluid in response to deformation.
Plates are able to shift and flex because it is flexible and soft.
