Lithosphere: Landforms, Rocks and Soil
Lithosphere: Landforms, Rocks and Soil
This topic covers the solid Earth and usually contributes 1 to 2 questions, most often on rock types or on the soils of India. Soil is the higher-yield half because it connects directly to agriculture, which the paper also asks about.
Interior of the Earth and Landforms
The Earth has three layers: the crust on the outside, the mantle below it, and the core at the centre. The crust is thinnest under the oceans and thickest under mountains.
- Mountains, plateaus and plains are the three major landforms.
- Volcanoes and earthquakes occur mainly along plate boundaries.
- An earthquake's point of origin inside the Earth is the focus; the point directly above it on the surface is the epicentre.
- Earthquake intensity is measured on the Richter scale using a seismograph.
✗ The epicentre is the point of origin inside the Earth | ✓ The focus is inside; the epicentre is directly above it on the surface
The Three Types of Rock
| Type | How it forms | Example |
|---|---|---|
| Igneous | Cooling of molten magma | Granite, basalt |
| Sedimentary | Compaction of deposited sediment | Sandstone, limestone |
| Metamorphic | Heat and pressure change an existing rock | Marble, slate |
Two transformation pairs are asked directly: limestone becomes marble, and shale becomes slate. Igneous rock is called primary rock because it forms first, and fossils are found mainly in sedimentary rock.
Soils of India
| Soil | Where found | Suited to |
|---|---|---|
| Alluvial | Northern plains, river valleys | Rice, wheat, sugarcane |
| Black (regur) | Deccan plateau, Maharashtra | Cotton |
| Red | Eastern and southern peninsula | Millets, pulses |
| Laterite | High rainfall areas, Western Ghats | Tea, coffee, cashew |
| Desert | Rajasthan | Drought-resistant crops |
| Mountain | Hill slopes | Tea, orchards |
Alluvial soil covers the largest area in India and is the most fertile. It is the soil of the Gangetic plain, which means it is the soil of almost all of Bihar — a link worth carrying into the Bihar topic later in this chapter.
Soil erosion is checked by contour ploughing, terrace farming, shelter belts and afforestation.
चूना पत्थर से संगमरस, शेल से स्लेट — दोनों कायांतरित शैल हैं।
TRE pointer: Soil-to-crop matching is the most predictable question in this topic, and the pair that decides it is black soil with cotton and alluvial soil with rice and wheat. For a Bihar candidate the alluvial row is doubly useful because it also answers questions about the state's own agriculture. The focus-and-epicentre swap is the other standard trap, and with −1/3 negative marking it is worth fixing once and for good.
60-Second Recap
- Crust, mantle and core are the three layers of the Earth.
- Focus is inside the Earth; epicentre is on the surface above it.
- Igneous from magma, sedimentary from deposits, metamorphic from heat and pressure.
- Limestone becomes marble; shale becomes slate; fossils occur in sedimentary rock.
- Alluvial soil covers the largest area in India and is the soil of the Gangetic plain.
- Black soil suits cotton; laterite suits tea, coffee and cashew.
Frequently Asked Questions
Which soil covers the largest area in India?
Alluvial soil, deposited by rivers across the northern plains and the river valleys. It is also the most fertile and supports rice, wheat and sugarcane. Since Bihar lies almost entirely in the Gangetic plain, alluvial soil is effectively the soil of the whole state.
What is the difference between focus and epicentre?
The focus is the point inside the Earth where an earthquake actually originates. The epicentre is the point on the surface directly above the focus, and it usually suffers the greatest damage. Questions routinely reverse the two definitions, so store them as a pair.
Which rock type contains fossils?
Sedimentary rock, because it forms by the gradual deposition and compaction of sediment, which can bury and preserve remains of plants and animals. Igneous rock forms from cooling magma and metamorphic rock from heat and pressure, so neither normally preserves fossils.
Which soil is best for cotton?
Black soil, also called regur soil, found mainly on the Deccan plateau in Maharashtra, Gujarat and Madhya Pradesh. It retains moisture well, which suits cotton. This soil-crop pair appears in almost every matching question set on Indian soils, so it is worth memorising first.