Base your answers to questions 80 through 82 on the generalized cross section of the grand canyon
represented below and on your knowledge of earth science. some rock layers have been labeled. the rock layers
have not been overturned.
the vishnu group is composed mostly of schist. explain how this rock formed. [1]

There are a lot of possible answers for this question. The Vishnu group is composed mostly of schist. The reason behind this is that  (1) Heat and pressure metamorphosed early rocks; (2) Regional metamorphism distorted these rocks. (3) There is presence of heat and pressure (3) Metamorphism is present in the process.

Geothermic gradient is the rate of increasing temperature with respect to increasing the depth in the earths interior. away from tech tonic plates boundaries, it is about 25-40 c/km (72-87 degrees f/mi) of depth near the surface in most of the world.

Answersource rock;