Examine the origins and characteristics of two types of rock—basalt and granite—that cover the ocean floor and much of the land surface of Earth, in this video from NOVA: Making North America: Origins. While early Earth’s undersea surface was made entirely of dark, heavy volcanic rock called basalt, over time, a lighter kind of rock formed. This rock, called granite, was buoyant. It floated up from the ocean floor and gathered in thick layers, creating landmasses that we call continents. This resource is part of the NOVA: Making North America Collection.
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