Inside Our Earth: A Deep Dive into Earth’s Structure and Composition

Our Earth, a dynamic sphere teeming with life, is not just what we see on the surface. Beneath our feet lies a vast and intricate structure, composed of several layers, each with its unique characteristics. Chapter 2 of the NCERT Grade 7 Social Science textbook, ‘Inside Our Earth’, offers a fascinating exploration of what makes up our planet.

1. The Layers of the Earth

Our planet can be visualized as a set of concentric layers:

- The Crust:

The Earth’s outermost layer, where we reside. Comprising solid rocks and minerals, it varies in thickness between 5km (under oceans) to 35km (on continents).

- The Mantle:

Located beneath the crust, the mantle extends to a depth of about 2,900 km. Composed of silicate rocks, it is a region of semi-molten rocks.

- The Core:

The innermost layer, subdivided into the outer core (liquid) and the inner core (solid). Predominantly composed of iron and nickel, it’s the hottest layer, with temperatures up to 5000°C.

2. Rocks and Their Types

Rocks, the building blocks of the Earth, are classified based on their origin:

- Igneous Rocks:

Born out of cooling and solidification of molten magma. Examples include granite and basalt. These rocks are the hardest.

- Sedimentary Rocks:

Formed from sediments like sand, silt, and clay. Often found in layered formations, examples include sandstone and limestone. Fossil records are typically found in these rocks.

- Metamorphic Rocks:

Originating from existing rocks undergoing changes due to heat and pressure. Examples include marble (from limestone) and slate (from shale).

3. The Wonderful World of Minerals

Minerals are naturally occurring substances with definite chemical properties. From the diamonds we adorn to the coal that fuels our industries, minerals play a vital role in our lives.

• How do minerals form? From cooling of molten materials, recrystallization of minerals, and by organic processes.

• Properties of minerals: Each mineral is unique, having specific color, hardness, density, and form.

4. Rocks versus Minerals

It’s essential to distinguish between rocks and minerals. While minerals are homogeneous, naturally occurring substances, rocks are aggregates of one or more minerals.

5. The Dynamic Earth

Our Earth is ever-changing. The continuous processes of erosion, deposition, and earth movements reshape its surface. This dynamism is attributed to the intense heat in the Earth’s core causing molten rocks to move, leading to phenomena like earthquakes and volcanoes.

Conclusion: The Earth - A Living Entity

‘Inside Our Earth’ not only introduces us to the Earth’s structure but also instills an appreciation for the dynamic processes shaping our planet. Recognizing the intricate interplay between various elements, from the core to the crust, is pivotal in understanding the world we inhabit.

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