The structure of Earth's interior.

The structure of Earth's interior.

Question - The structure of Earth's deep interior cannot be studied directly. But geologists use seismic waves to determine the structure. Discuss and describe earth's interior

The study of earth's surface and its interior falls under geology. Not much direct knowledge about the earth's interior is accessible and so most of our information comes from seismic waves, the vibrations caused in the earth's body. Seismic waves are categorized under two groups:

P-waves that are longitudinal pressure waves traveling through solids and liquids.
S-waves which are transverse capable of traveling in solids but not in liquids.

These seismic waves generated by earthquakes, volcanoes and by impacts produced artificially by explosions and mechanical devices, provide considerable knowledge about the interior.

Earth's interior structure:

The earth is divided into four main layers: the inner core, outer core, mantle, and crust.

Majority of the earth's mass is in the mantle, which is composed of iron, magnesium, aluminum, silicon and oxygen silicate compounds. The crust is made up of calcium and sodium aluminum-silicate minerals and is thinner than rest of the layers. Due to its relatively cooler temperature, the crust is rocky and brittle, giving rise to fractures during an earthquake.

Crust: Crusts are mainly of two types

a) thin oceanic crust which lies beneath the ocean basins and
b) the thick continental crust that underlies the continents.

These are found made up of different types of rock. The thin oceanic crust is composed primarily of basalt and the thicker continental crust of granite. The continental crust , due to its low density, allows it to float on the much higher density mantle below.

Mantle: Earth's mantle is thought to be composed mainly of an olivine-rich rock and has different temperatures at different depths. The temperature is lowest right below the crust and increases with depth. The highest temperatures are seen where the mantle material comes in contact with the hot core. This gradual increase of temperature with depth is known as the geothermal gradient which is responsible for different rock behaviors that divide the mantle into two zones. Rocks in the upper mantle are cool and brittle enough to break under pressure producing earthquakes, while those in the lower are hot and soft, flowing when subjected to forces rather than breaking. The lower limit of brittleness forms the line between upper and lower mantle.

Core: Iron is the main element of the core and is the hottest so much so that the outer core is molten with about 10% sulphur. The inner core, due to extreme pressure remains solid which has mainly of an iron and nickel alloy. This composition is taken based upon calculations of its density and upon the fact that many meteorites are iron and nickel alloys. The core is the earth's source of internal heat because it contains radioactive materials which release heat as they break down into more stable substances.

The core is divided into two different zones:

a) The outer core is a liquid due to the high temperatures melting the iron nickel alloy.
b) the inner core is solid even though its temperature is higher compared to the outer core.