Asthenosphere
- The upper layer of the Earth’s mantle, separated from the above lithosphere by the Moho.
- The rock is less rigid than that below and above but can transmit transverse seismic waves.
- There is relatively low resistance to plastic flow and convection is thought to occur.
- Reaches depths between approximately 80 and 200km below the surface (even as deep as 700 km)
- Temperatures from 1300° C
- Mafic rocks: minerals such as olivine which produce volcanic rocks like basalt
Crust
- Outermost layer of the planet
- Composed of a igneous, metamorphic, and sedimentary rocks
- Temperature ranging from surface temperature to 400°C
- Solid rock
- Surface and body waves able to pass through
Inner core
the innermost part of a core, specif. a solid sphere in the middle of the fluid core such as the iron-nickel core of the Earth.
- 5150km deep to centre
- 7000°C (radioactive decay)
- Very dense (13.5g/cm3)
- 80% iron, 20% nickel
- Solid, two parts with crystals aligned in opposite directions
- Only P waves pass through but their refraction at the core-mantle boundary creates a ring ‘shadow zone’ between 105° and 140° from the focal point
Continental crust
- Up to 70km thick
- Less dense than oceanic crust
- Granite
- Cannot be created or destroyed (older rocks)
Oceanic crust
- Up to 7km thick
- Denser than continental crust
- Basalt
- Can be created or destroyed (newer rocks)
Moho
The Mohorovicic Discontinuity, or “Moho,” is the boundary between the crust and the mantle. lying at a depth of about 10–12 km under the ocean bed and 40–50 km under the continents.
Sedimentary rocks
Rock that has formed through the deposition and solidification of sediment, especially sediment transported by water (rivers, lakes, and oceans), ice ( glaciers ), and wind. Sedimentary rocks are often deposited in layers, and frequently contain fossils. Note : Limestone and shale are common sedimentary rocks.
Sedimentary rocks are formed from sediments that have settled at the bottom of a lake, sea or ocean, and have been compressed over millions of years.
Igneous rocks
Igneous rock (derived from the Latin word ignis meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. Rocks formed by the cooling and solidifying of molten materials. Igneous rocks can form beneath the Earth ‘s surface, or at its surface, as lava.
Note : Granite, solid volcanic lava, and basalt are examples of igneous rock.
Metamorphic rocks
A metamorphic rock is a type of rock which has been changed by extreme heat and pressure. Its name is from ‘morph’ (meaning form), and ‘meta’ (meaning change). The original rock gets heated (temperatures greater than 150 to 200 °C) and pressured (1500 bars). This causes profound physical and/or chemical change.
Rock that was once one form of rock but has changed to another under the influence of heat, pressure, or some other agent without passing through a liquid phase. Note : Examples are marble, which can be formed from limestone, and slate, which is formed from shale.
