Earth's crust
Earth's Crust
The Earth's crust (pronunciation: /ɜːrθz krʌst/) is the outermost shell of a terrestrial planet. It is the thinnest layer of the Earth, constituting less than 1% of the planet's volume.
Etymology
The term "crust" originates from the Latin word "crusta", which means "hard shell". The term "Earth" is derived from the Old English word "eorþe", which has Germanic origins.
Definition
The Earth's crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is composed of a great variety of igneous, metamorphic, and sedimentary rocks. The crust of the Earth is underlain by the mantle. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity.
Types of Crust
There are two types of crust: the oceanic crust and the continental crust. The oceanic crust is 5 km (3 mi) to 10 km (6 mi) thick and is composed primarily of basalt, diabase, and gabbro. The continental crust is typically from 30 km (20 mi) to 50 km (30 mi) thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust but rare to absent in the oceanic crust.
Related Terms
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