Inside Our Earth

We walk, run, jump, dance and skip on the earth. But have you ever wondered about what is present inside our earth? The earth is made up of minerals as well as an amazing variety of rocks. As a child, I was simply fascinated with rocks and used to collect them from whichever place I used to visit. Let’s explore more about the rocks that are present inside our earth as well as know how they are formed.

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Rocks and Minerals – Treasures Inside our Earth!

So what exactly is the difference between rocks and minerals? A rock is basically a natural mass of minerals found in the earth’s crust while minerals are freely occurring substances inside our earth having a definite chemical composition

Various Types of Rocks

Rocks inside our earth are broadly classified into 3 types

• Igneous rocks
• Sedimentary rocks
• Metamorphic rocks

This classification is mainly based on their texture and the process by which they were formed.

Igneous Rocks

When the lava from a volcano melts and cools down, it forms igneous rocks. These rocks are first to be formed and hence are also known as primary rocks. They can be further categorized into two types:

• Extrusive Igneous Rock
• Intrusive Igneous Rock

The most important point of difference between intrusive and extrusive rocks is that the intrusive igneous rocks crystallize below earth’s crust, resulting in the formation of large crystals due to the slow cooling down process. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite.Whereas, extrusive igneous rocks that are formed when magma flows out on the earth’s surface, where they cool quickly to form small fine crystals.

Sedimentary Rocks

The deposition of smaller particles of rock in the form of layers results in the formation of sedimentary rocks, also known as strata while smaller particles that are formed from these large rocks are known as sediments. At times, during the formation of these rocks, preserved remains of plants and animals get trapped within these layers. These are what we call “fossils”.

Metamorphic Rocks

The world metamorphosis is synonymous with “transformation”. Rock that was once a different form of rock but has transformed to another over time under the influence of heat and pressure, or without passing through a liquid phase is known as metamorphic rock. For example, Limestone undergoes metamorphosis to form marble while slate is formed from shale.

The Rock Cycle

The rock cycle is the process that occurs inside our earth by which rocks of one kind changing into rocks of another kind. The three kinds of rocks can interchange into each other under the influence of physical processes: cooling, melting, heat, erosion, compacting (squeezing tightly together), cementing, and pressure.

When heated deep underground, rocks become magma (liquid rock). We call this magma present above the ground as lava. The particles from rock erosion and weathering go on to become sedimentary rocks.

• Igneous rock is hardened magma, which can happen above or below ground. It can melt into magma, erode into sediment, or be pressed tightly together to become metamorphic.
• Metamorphic rock is formed as a result of squeezing of sedimentary or igneous rocks under extreme temperature and pressure. It can either get eroded to form a sediment or melt into magma. These extreme conditions mostly occur deep inside the mountains.
• Sedimentary rock is compacted sediment which can not only come from any of the other rocks, but also from the remains of living things. It can erode back into sediment, or be pressurized into metamorphic rock.

Thus these forms of rocks keep on interchanging into one another and the process occurs in no particular order. It goes on forever. Earth provides several favourable conditions and factors for the changing of rocks. These include:

• Wind and Water
• Movement of Tectonic plates
• Heat and Pressure
• Subduction

Wind, as well as water, can create sediment from rocks, whereas the movement of one tectonic plate against another creates enormous heat and pressure which affects rocks greatly. Subduction converts all kinds into magma, which eventually rejoins the cycle as igneous rock

Questions For You

Q1. Which of these are the types of igneous rock?

1. Intrinsic
2. Extrinsic
3. Intrusive
4. Extrusive

Answer. Intrusive as well as Extrusive are the two types of igneous rocks.