Inside The Earth

EARTH: Interior of The Earth

Earth, the third planet in our solar system, formed around 4.5 billion years ago. Initially, it was a scorching lava ball, but due to rains and thunderstorms, its outermost layer gradually cooled down. Now, we inhabit it, obtaining food, air to breathe, and water to drink. However, Earth is not just a giant ball; it consists of four main layers, which we will discuss below.


The outermost layer of Earth is called the crust,just like crust on fruits, vegetables, and eggs. Just like these food items have a crust, Earth’s first layer is the crust. Our Earth, formed 4.5 billion years ago, underwent changes leading to the development of Earth’s crust.So, the crust formed around 4 billion years ago. Among all Earth’s layers, the crust is the thinnest, constituting just 1% of the Earth’s total mass. Earth’s composition includes silicate minerals, carbonates, quartz, feldspar, metallic minerals, mica, aluminosilicates, and olivine. It comprises three types of rocks: igneous, sedimentary, and metamorphic. While the crust may only contribute 1% to the Earth’s mass, it hosts countless geographical features. Mountains, rivers, lakes, islands, forests, valleys, deserts, plateaus, plains, canyons, peninsulas, deltas, caves, hills, oases, volcanoes, waterfalls, gorges, tundras, and cliffs. Crust is the outer layer through which we get water via rivers, lakes, boreholes, and wells. People drill into the Earth’s layer to extract water.

Earth’s crust is divided into two parts,

  • Continental crust
  • Oceanic crust

Continental crust vs Oceanic crust:

So, in simple terms, there are two types of crust: the one we live on, which includes mountains, valleys, and plateaus (known as continental crust), and the one beneath the oceans (called oceanic crust). In terms of thickness, continental crust is three times thicker than oceanic crust, with continental crust measuring 75 km and oceanic crust ranging from 6-11 km thick. The density of oceanic crust is 3 g/cm³, while the density of continental crust is 2.7 g/cm³. Oceanic crust is denser than continental crust due to its composition of dense volcanic rocks like basalt, whereas continental crust consists of lighter and less dense rocks like silica and aluminum. The higher density of oceanic crust causes it to sink below, while continental crust remains afloat. If continental crust were denser, it would gradually submerge. Both types of crust experience volcanic eruptions; oceanic crust subducts into the Earth, leading to volcanic explosions. Continental crust supports human habitats, agriculture, and geographical features, while oceanic crust is vital for marine life and serves marine and shipping routes.


After Earth’s first layer, the crust, comes the intermediate layer known as the mantle. The boundary separating the crust and mantle is called the Mohorovičić discontinuity. It begins 42 km beneath the Earth’s surface and has a total thickness of 2900 km, making it the thickest layer. The mantle constitutes about 85% of the Earth’s total mass. In terms of temperature, the mantle is hotter than the crust, ranging from 2500°C to 2200°C. Its density, at 4.5g/cm³, is higher than that of the crust. The mantle primarily consists of silicate rocks.

Upper & Lower mantle:

Earth’s mantle is subdivided into two parts,the upper mantle and the lower mantle. The boundary separating these parts is called the Repetti discontinuity. As we go deeper into the Earth, both temperature and density increase. The temperature of the upper mantle ranges from 500 to 900 degrees Celsius. The upper mantle is also referred to as the asthenosphere.Astheno” means weak, indicating that in the asthenosphere, nothing remains in a solid state; everything is in a molten form. This is why the asthenosphere is the primary source of magma. Following the dense and hot asthenosphere, the lower mantle begins, which exists in a solid state. There is an interesting fact, or rather a myth, that suggests the entire mantle is in a molten state, which is not true.


After the mantle, the last layer of the Earth is the core. The boundary separating the mantle and core is known as the Gutenberg discontinuity. The core is the central part of the Earth, roughly equivalent in size to our moon. It begins at a depth of 2900 km. The core is divided into two parts: the outer core and the inner core. Now, let’s discuss them separately.

Outer Core:

The outer core begins at a depth of 2900 km and extends to 5100 km. Composed of iron and nickel, it reaches extremely high temperatures of 5000°C, causing the iron-nickel rocks to exist in a molten state. The outer core is crucial for Earth as it plays a significant role in generating Earth’s magnetic field.

Inner Core:

The inner core follows the outer core, and the discontinuity separating the two cores is known as the Lehmann discontinuity. The temperature in the inner core ranges from 5000°C to 7000°C, making it the hottest layer of the Earth, even hotter than the surface of the sun. However, despite the high temperature, the iron and nickel in the inner core exist in a solid state. The reason for this is the immense pressure in addition to the temperature. When both temperature and pressure are extremely high, they cause the materials to solidify. This solid state of the inner core is why it is often referred to as the NIFE layer, where Ni represents nickel and Fe represents iron.

So, these are the layers of the Earth, each existing in a different state with unique temperatures, densities, and pressures. The Earth, which appears as a cool land and water form from the outside, reveals its intricate layers when explored. Understanding these layers gives us insight into the complexities of nature and how everything works seamlessly. It makes us realize the importance of nature’s balance. If we imagine scenarios like magma from the Earth’s interior emerging, it emphasizes the significance of the stability we currently enjoy. Gratitude for the wonders of our planet is certainly warranted.



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