Consider a seafloor spreading zone creating 1 centimeter of new crust over its entire 1000 kilometers length every year.
a) how many square kilometers of surface will this create in 100 million years? express your answer in km squared
b) what fraction of earth's surface does this constitute?

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.