When the surfaces of solid materials scrape and grind against each other , it’s called ?

In 1915 the german geologist and meteorologist alfred wegener first proposed the theory of continental drift, which states that parts of the earth's crust slowly drift atop a liquid core. the fossil record supports and gives credibility to the theories of continental drift and plate tectonics.

Acontinental polar air mass foms in

Whats the biggest sea in the world?