I want to know what the boundaries of continents are.

Why would the crystals in an intrusive igneous rock be larger than the crystals in a chemical sedimentary rock? a. intrusive rocks form beneath the earth's surface, so they cool very slowly, which produces larger crystals. b. chemical sedimentary rocks form from dissolved substances on the earth's surface with very high heat and cool very slowly, which produces smaller crystals. c. chemical sedimentary rocks and intrusive rocks have crystals of the same size. o d. chemical sedimentary rocks form deep in the earth, so they cool slower, which produces small crystals. € read question correct:

The first atomic explosion was detonated in the desert north of alamogordo, new mexico, on july 16, 1945. what percentage of the strontium-90 ( yr) originally produced by that explosion still remains as of july 16, 2016?

In plate tectonics, why is the north american plate tectonically inactive?