When earth was initially forming it was molten all around. Heavier materials such as nickel and iron were sunk to the centre due to force of gravity. The lighter material was lifted to the surface and when cooling began these lighter materials made the hard crust across the surface.

The earth consists of three layers namely crust, mantle and core (Steward and Kathleen 18). The crust is the outermost layer comprising of rock. It is brittle and cool as compared to other layers.  The crust Is further divided into plates. The crust is the only layer that is able to sustain life, and the thinnest of the three layers of the Earth. The thinnest part of the crust is under the ocean and it is known as oceanic crust whiles the thickest of the crust being the continents. The crust cracks and breaks easily because it is very cold as compared to the mantle and the core. Valuable resources such as oil, water, and gas are found on earth’s crust.

Continental crust

It is on the continent that we live and build great cities. The continental crust is about 35 and 7 kilometers thick (Vogt 13). This means that the continental crust is about seven times thicker than the oceanic crust. Sometimes the name sial is used to refer to the continental crust. It is commonly used by geologists. The sial is made of silica and aluminum rich rocks. These rocks are to as felsic especially y geologists. This is because they have high levels of feldspar which is an aluminum silicate mineral series. The continental crust is less dense than oceanic crust because of higher amounts of aluminum and less amounts of magnesium and iron. Its density is between 2700-2800 kilograms per cubic meter.

Oceanic crust

Oceanic crust measures 5 to 7 kilometers thick (Vogt 13). It is made up of brittle minerals like calcium and sodium. Oceanic crust can also be known as sima. The rocks constituting this layer are rich in silicate and magnesium minerals. Sometimes sima can come to the surface and when it does it is basalt in nature, this explains why oceanic crust is sometimes referred to as 'basalt layer' of the crust. Oceanic crust has diverse features just as the continental crust. Landforms such as “plains, ridges, trenches, valleys, and seamounts are found on the oceanic crust” (steward 30). It is on the oceanic crust that all earth’s water is collected.

Earth mantle

The mantle is a hot fluid rock that lies immediately below the earth’s crust. It is also the thickest of the three layers of earth. It is about 1800 miles (2900 km) thick. Like the earth crust, the mantle has two layers too. The temperatures in this layer range from 1600°F in the upper mantle, close to the crust, and about 4000°F in the lower mantle, closer to the core. The fluid rock flows and moves due to the wide range of temperatures in the mantle. Since the mantle is close to the crust when the fluid rock moves the crust also moves. The inner layer of the mantle does not move as freely as the outer layer as one would expect, because of the high pressure exerted on the inner mantle.

The core

The core is the innermost layer of the earth. It is comprised of two layers namely outer core and the inner core. The outer core is consisted of molten metal. Within the outer core lays the inner core. The inner core is about 1200 kilometers thick while the outer core is around 2300 kilometers thick (Vogt 10).The inner core is a heavy ball of solid metal. Temperatures inside the inner core reach about 9032°F. These are very high temperatures that cause the metals constituting the inner core to melt. However, due to extreme pressure from the overlying weight of the layers above, iron and nickel atoms are squeezed so hard that they become solid. They remain in this state as there is no space for them to spread and become liquid. However the outer core remains partially molten. The high temperatures in the core is what gives energy to move rocks in the mantle.

Lithosphere

Lithosphere consists of the crust and the outer layer of the mantle. The earth crust is made up of seven land masses called continents and the oceans. The seven land masses are Asia, Europe, Africa, South America, North America, Antarctica, and Australia (Wright 449). Asia is the largest continent by size while Australia is the smallest. The biggest portion of the earth is occupied by water, 70% of the earth, (Woodward 4). There are five principle oceanic areas namely Atlantic Ocean, Arctic Ocean, Indian Ocean, Pacific Ocean, and Southern Ocean (Aloian & Bobbie 4).

The crust has diverse landforms that result from two main forces, the forces that build and those that tear down (Vogt 9). When building forces win mountains, islands and broad plains are created. Where tearing forces take the lead an entire island is sank into the sea. However, sometimes neither the building forces nor the tearing forces win. In such an occurrence a wide plateau is lifted and a great river makes a deep gorge.

The plates that make up Earth’s crust drift on top of the molten mantle. Some plates pull away from each other, while others push toward each other. Some plates slide past each other. A plate boundary is where these plates meet.

How earth layers are studied

Because of the high temperature in the earth core and mantle it is not possible for man to travel there to study the earth layers. Light cannot also travel to the core of the earth because rocky nature of the earth. With these limitations, alternative ways have been devised to help in studying the nature and composition of earth. They include observations of topography and plumbing, observations of rock outcrop, samples of materials brought to the earth surface from the depths of the earth by volcanic activity, analysis of the seismic waves, and measurements of the earth’s field of gravity.

Conclusion

Earth is surely an awesome planet. The only one that is able to support life. The structure of the earth can be divided into three main layers, crust, mantle, and core. Each of these divisions can further be subdivided into smaller layers. The top most layer is the crust, followed by the mantle and the core is the innermost layer. The crust is further subdivided into oceanic crust and continental crust. The mantle is subdivided into outer and inner layer. The core is similarly subdivided into outer and inner layers

The crust is solid in nature and very cold compared to other layers. As a result the crust breaks and cracks easily. The mantle is made up of molten metal that flows slowly. the temperatures are relatively high but not as those of the core. The temperatures in the core are very high to melt the metals that constitute the core. However the inner core is in solid form due high pressure from the overlying materials.

Earth is endowed with great resources such as water, gas, and oil found in the earth crust. Iron, magnesium, aluminum, sodium and nickel are some of metals found in the mantle and the core. Study of earth’s internal structure has been made possible through analysis of seismic waves, observation of earth’s topography and other methods.

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