Crust (geology) the crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity. The crust of the Earth is of two distinctive types: Because both continental and oceanic crust are less dense than the mantle below, both types of crust "float" on the mantle. This is isostasy, and it's also one of the reasons continental crust is higher than oceanic: continental is less dense and so "floats" higher. As a result, water pools in above the oceanic crust, forming the oceans. The temperature of the crust increases with
Geology of Nebraska Geology of Nebraska The geology of Nebraska is part of the broader geology of the Great Plains of the central United States. Nebraska's landscape is dominated by surface features, soil and aquifers in loosely compacted sediments, with areas of the state where thick layers of sedimentary rock outcrop. Nebraska's sediments and sedimentary rocks lie atop a basement of crystalline rock known only through drilling. The land that is today Nebraska originated as a juvenile crust expansion of the continent Laurentia—today part of the North American Craton and the core of the North American continent—between 1.8 and 1.6 Ga (billion years