Inside Our Earth
Overview
What is inside the Earth? We cannot dig all the way through (even the deepest drilling goes only a little way in), but scientists have discovered three layers inside the Earth — crust, mantle, and core. And the rocks from these layers are what make our homes, roads, and everything around us.
Typed Notes
Earth's Three Layers
(1) Crust — the outermost thin layer (70 km thick under mountains, only 8-10 km thick under oceans). We live on this layer. It has two parts: upper SIAL (silica+aluminium — lighter) and lower SIMA (silica+magnesium — heavier). (2) Mantle — lies below the crust; the largest part of the Earth; made of hot, semi-solid rock. (3) Core — the innermost layer, the hottest part (4500°C and above); made of iron and nickel — hence called NIFE (Ni+Fe). The heat of the core is the root cause of volcanoes and plate movement.
Igneous Rocks — Born from Fire
When magma (molten rock) from inside the Earth comes out through a volcano or cools down inside the Earth itself — igneous rock is formed (Latin 'ignis' = fire). Two types: Extrusive — magma comes out and cools quickly — basalt (Deccan Plateau); Intrusive — cools slowly inside the Earth — granite (large crystals, used in home flooring). Igneous rocks are the oldest rocks — the Earth began with these.
Sedimentary and Metamorphic Rocks
Sedimentary — formed when layers of sand, mud, and rock particles carried by rivers, wind, and oceans settle and pile up one over another (sandstone, limestone, coal). That is why fossils (remains of ancient living beings) are found in them — scientists read Earth's history through these fossils. Metamorphic — formed when any rock is changed by heat and pressure (Greek 'metamorphose' = to change): limestone → marble (Taj Mahal), clay → slate, coal → graphite/diamond. The marble on home floors and the slate on rooftops — all are metamorphic rocks.
Rock Cycle and Minerals
Rocks never stay in one form forever: igneous rocks are broken down by wind and water — sediments form → sedimentary rocks; if they go deeper — heat and pressure change them into metamorphic rocks; going even deeper they melt — magma forms → igneous rocks again. This endless cycle is called the rock cycle — Earth's own recycling system. Metals and non-metals found inside rocks are called minerals: iron, bauxite (aluminium), coal, petroleum, gold. Homes, industries, and vehicles all run because of these. That is why we must talk about conserving rocks and minerals.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Earth's 3 layers: Crust (outermost, thinnest — this is where we live), Mantle (middle, largest), Core (innermost, hottest — made of iron and nickel).
- 02Crust has 2 parts: SIAL (upper — silica+aluminium, lighter) and SIMA (lower — silica+magnesium, heavier). The core is called NIFE (nickel+ferrous).
- 03Rocks are of 3 types: Igneous (formed by cooling of magma — granite, basalt), Sedimentary (formed by layers of sand and mud — sandstone, limestone, coal; fossils are found in these), Metamorphic (changed by heat and pressure — limestone→marble, clay→slate).
- 04Rock cycle: rocks keep changing endlessly — igneous → weathering produces sediments → sedimentary → heat-pressure makes metamorphic → melting produces magma → igneous again.
- 05Minerals: metals and non-metals found inside rocks (iron, coal, petroleum, gold) — industries run because of these.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
Write the names of Earth's three layers and one fact about each.
What are the two types of igneous rocks? Give examples.
In which rocks are fossils found, and why?
What do limestone and clay become after metamorphism?
What is the rock cycle? Explain in one line.
What are minerals? Give two examples.
Earth has 3 layers: crust (SIAL+SIMA), mantle, and core (NIFE). Rocks are of 3 types: igneous (granite/basalt), sedimentary (contain fossils — sandstone/limestone/coal), and metamorphic (limestone→marble). The rock cycle never stops. Minerals (iron, coal) — the fuel of industry.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Which metals is the core made of?
Q2.What type of rock is basalt?
Q3.What does limestone become after metamorphism?
Q4.What is the heavier lower part of the crust called?
Mark karo — dashboard par progress dikhega.