Скачать или смотреть NCERT Class 7 Geography Chapter 2 | 🔥 Inside the Earth | Full Explanation, Summary & Important

Geography Class 7 – Chapter 2: Inside the Earth | Full Explanation, Summary & Important Concepts

Welcome to an in-depth exploration of “Inside the Earth”, the 2nd chapter of Class 7 Geography. This video is designed to help students, UPSC aspirants, and curious learners understand the structure of the Earth, its layers, rocks, and minerals in a simple yet comprehensive way. Whether you are revising for UPSC Prelims, school exams, or competitive geography tests, this explanation covers every detail from crust to core, types of rocks, discontinuities, and geological processes.

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1️⃣ Introduction to the Earth’s Interior
• Earth is a layered planet with different compositions and physical states.
• Understanding Earth’s interior is crucial for geology, seismology, and natural resource studies.
• The Earth has three major divisions: Crust, Mantle, Core, and several discontinuities that mark changes in composition and density.

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2️⃣ Layers of the Earth

a) Crust
• Thinnest layer, 5–70 km thick.
• Made of SIAL (Silica + Aluminium) in continental crust and SIMA (Silica + Magnesium) in oceanic crust.
• Supports life and human civilization.

b) Mantle
• 2900 km thick, composed of silicate rocks rich in Mg and Fe.
• Semi-solid and responsible for convection currents, which drive plate tectonics.

c) Core
• Divided into Outer Core (liquid, Fe & Ni) and Inner Core (solid, Fe & Ni).
• Generates Earth’s magnetic field.
• Temperatures up to 5000–6000°C.

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3️⃣ Discontinuities in the Earth
• Boundaries between layers where physical and chemical properties change abruptly.
• Major discontinuities:
1. Conrad Discontinuity – upper & lower crust.
2. Mohorovičić (Moho) Discontinuity – crust & mantle, seismic waves increase speed.
3. Repetti Discontinuity – upper & lower mantle.
4. Gutenberg Discontinuity – mantle & outer core, S-waves disappear.
5. Lehmann Discontinuity – outer & inner core.

UPSC Tip: These discontinuities are discovered using seismic wave analysis.

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4️⃣ Rocks and Minerals

Rocks: Naturally occurring aggregates of minerals.
• Igneous Rocks – Formed from cooling magma or lava.
• Basalt (extrusive) – fine-grained, mafic, found in surface lava flows.
• Granite (intrusive) – coarse-grained, felsic, forms underground.
• Sedimentary Rocks – Formed by compaction of sediments; often contain fossils.
• Metamorphic Rocks – Formed under high heat and pressure, altering existing rocks.

Minerals: Naturally occurring inorganic substances, e.g., gold, coal, petroleum.
• Minerals are economic resources; rocks are building resources.

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5️⃣ Why the Crust is Rich in Silica and Aluminium
• During early Earth differentiation, heavy elements (Fe, Ni) sank to form the core.
• Lighter elements like Si and Al floated upward → forming SIAL crust.
• Partial melting and magmatic differentiation concentrate silica-rich rocks in continental crust.

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6️⃣ Basalt vs Granite (Extrusive vs Intrusive Rocks)

Feature Basalt Granite
Location Surface lava (extrusive) Underground magma (intrusive)
Cooling Rapid Slow
Texture Fine-grained Coarse-grained
Composition Mafic (Fe, Mg) Felsic (Si, Al)
Color Dark Light

UPSC Insight: Cooling rate determines crystal size and rock type.

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7️⃣ Summary
• Earth is layered: Crust → Mantle → Core.
• Discontinuities mark sharp changes in density, composition, and state.
• Rocks are classified into Igneous, Sedimentary, Metamorphic.
• Basalt is extrusive & mafic; Granite is intrusive & felsic.
• Minerals are resources, crust is SIAL-rich due to light elements floating upward.
• Knowledge of Earth’s interior is critical for geology, earthquake study, and natural resource exploration.

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