- 2068 Baisakh · 3 marks
Short note: Crust
Short answer
The crust is the outermost thin solid layer (5-70 km), composed of igneous, sedimentary and metamorphic rocks. Continental crust is thicker, granitic (sial, 2.7 g/cm³); oceanic crust is thinner, basaltic (sima, 3.0 g/cm³). It forms the lithosphere with the upper mantle and is where all engineering and tectonic activity occur.
Write a short note on the crust of the earth.
The crust is the outermost, thin, rigid, solid layer of the Earth, lying above the Mohorovicic (Moho) discontinuity. It makes up less than 1% of Earth's volume.
Types
- Continental crust: thickness 30-70 km (thickest below the Himalaya); mainly granitic (rich in silica and aluminium, called sial); density about 2.7 g/cm³; old rocks, up to 4 billion years.
- Oceanic crust: thickness 5-10 km; basaltic (silica and magnesium, sima); density about 3.0 g/cm³; young, less than 200 million years.
Features
- Composed mainly of igneous, sedimentary and metamorphic rocks.
- Most abundant elements: oxygen (46.6%), silicon (27.7%), aluminium (8.1%), iron (5%), calcium, sodium, potassium, magnesium.
- Temperature rises about 25-30 °C per km depth.
- Together with the top of the upper mantle, it forms the lithosphere, which is broken into plates.
The crust is the part on which all civil engineering works are built, and it is the layer where earthquakes, folding and faulting occur.
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