What is the thick, old crust of earth known as?

What are seismic dampers and why are they important?

How did the korean war impact the elections of 1952?

What evidence does the writer give to support his argument about coral reefs? a) he speaks of the activities of coral polyps. b) he describes the composition of the great barrier reef. c) he emphasizes the ways in which coral reefs are fragile. d) he points out the ways that scientists do research on the reefs.