Inside Our Earth

Interior of the Earth  : Chapter Summary

The earth is made up of several layers of material arranged on top of each other. The outermost layer is the thinnest layer, called the solid crust, further classified into oceanic crust and continental crust. The oceanic crust, the crust beneath the oceans, is only 5 kilometres thick while the continental crust is around 35 kilometres thick.

The oceanic crust, is made up of silica and magnesium, and is called sima while the continental crust is composed of two minerals: silica and alumina and called sial. The next layer is a highly viscous layer called the mantle. The mantle is 2,900 kilometres deep and is thickest among all the layers forming 83% of the earth’s volume. The material inside the mantle is known as magma.

When the earth’s crust gets ruptured, hot molten magma, ash and gases come out from the core to the surface of the earth. This results in the formation of a volcano and the magma released on the surface of the earth is called lava.

Below the mantle is the core of the earth divided into outer core and inner core. The outer core is mainly made up of nickel and iron, called as nife. The materials in the outer core are in a liquid state. The temperatures in the inner core range from 5000 to 6000 degree Celsius. The core as a structural element of the earth was discovered in 1906 by R.D. Oldham.

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Rocks and Minerals: Chapter Summary

A rock is a natural mass of minerals found within the earth’s crust while minerals are substances that have a definite chemical composition and occur freely in nature.

Rocks can be are classified in three types on the basis of their texture and the process of formation i.e. igneous, sedimentary and metamorphic rocks. The igneous rocks are formed when molten lava from a volcano cools down. These rocks are also known as primary rocks as they are the first to be formed and are further of two types: extrusive and intrusive.

Extrusive igneous rocks are formed when magma flows out on to the earth’s surface and cools down rapidly by air to form solid fine-grained rocks. Intrusive igneous rocks are formed when molten magma cools down inside the earth’s crust.

Must Read:  Inside Our Earth Solved Question Answers

Sedimentary rocks are formed by the sedimentation or deposition of smaller rock particles in layers called beds or strata. The smaller particles formed from these large rocks are called sediments.

Sometimes, during formation, sedimentary rocks may contain preserved remains of plants and animals trapped within the layers. These remains are called fossils.

Metamorphic rocks are formed when igneous and sedimentary rocks undergo great heat and pressure over time.

Rock Cycle : Chapter Summary

A rock changes from one type to another when subjected to certain conditions and the process is known as the rock cycle.

When lava cools down, it solidifies to form igneous rocks or primary rocks while sedimentary rocks are formed when igneous rocks are broken down into small particles, carried to other places, and deposited in layers.

When igneous and sedimentary rocks undergo great heat and pressure, they change to form metamorphic rocks over time. However, metamorphic rocks, under great heat and pressure can further melt to form molten magma. The magma returns back to the magma chamber under the earth’s crust.

This magma again cools down and form igneous rocks. This process leads to the rock cycle.

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