Earth’s Interior (Structure of the Earth)
The structure of earth is in spherical form and is composed of four layers, three solid and one liquid which is in the form of molten metal, and is hot as the surface of the sun. A fruit such as a peach are in analogy to earth’s interior. A fruit with large pits, when cut in two pieces has three parts which are similar to earth’s crust.
In 1692, Edmund Halley brought forward the idea that the Earth’s structure is hollow shell approximately of 500 miles.
1. Earth’s Crust
There are 2 types of crusts made up of different types of rock:
i. Thin oceanic crust that’s behind the ocean basins composed primarily of basalt
ii. Thick continental crust that lie beneath the continents composed primarily of granite. It has low density which allows it to float on mantle which has much higher density.
2. Earth's mantle
Earth's mantle is mainly made up of olivine-rich rocks. It has varying temperatures at different depths. The maximum temperature is where mantle is in touch with the heat-generating core. The increase of temperature is acknowledged as the geothermal gradient which is accountable for different behaviors of rock. These behaviors separate the mantle into 2 zones. Upper mantle rocks are cool and fragile which are fragile enough to fracture under pressure and generate earthquakes, whereas lower mantle rocks are hot and soft. However, rocks in the lower mantle are supple and in liquid form. The lower limit of this frail behavior is the edge amid the upper and lower mantle.
3. Earth’s Core
It is thought that this part is mainly composed of an iron and nickel alloy. This presumption is made on the basis of its density and on the information that several meteorites are iron-nickel alloys and which are considered to be part of earth’s interior. The core contains radioactive materials that release heat on its break down. The core is divided into 2 different zones:
i. The outer core is liquid because the high temperatures melt the iron-nickel alloy.
ii. The inner core is a solid although its temperature is more than the outer core because the pressure generated by the overlying rocks is remarkably high and it keeps the atoms tightly packed together.