NCERT Solutions for Class 9th Social Science Chapter 2 Shaping of the Earth’s Surface
Updated on 2026-09-19
About this chapter
The Earth has three main layers — crust , mantle and core . The crust together with the upper mantle makes the rigid lithosphere (about 100 km thick in Fig. 2.1); below it lies the hot, partly molten asthenosphere (about 200 km), which is what lets the plates move at all. The lithosphere is broken into tectonic plates — continental, oceanic and mixed — that creep along at a few centimetres a year. Fig. 2.3 names seven major plates: Pacific, Eurasian, African, North American, South American, Indo-Australian and Antarctic. Plates move because of convection currents in the mantle: heated material rises, cooler material sinks, and the circulating mantle pushes and pulls the plates. Fig. 2.2 splits the total interior heat flow between crust (24%), upper mantle (22%), lower mantle (32%) and core
- Chapter opening
- The Ring of Fire in Fig. 2.4
- Does India have a risk of earthquakes? (Fig. 2.5)
- The photograph in Fig. 2.6
- Erosion caused by (a) water and (b) wind
- The Sundarbans delta (Fig. 2.13)
- The Chamoli flood of February 2021 (Fig. 2.20)
- Landforms around your school or home
- Completing the disaster exercises on pages 33–36
- The chapter's recap points, expanded
Quick revision
| Term | What it means | Where it appears in the chapter | Example from the book |
|---|---|---|---|
| Lithosphere | The rigid outer layer of the Earth — the crust plus the upper mantle. It is this layer that is broken into plates. | Page 14, Fig. 2.1 | Shown as about 100 km thick in Fig. 2.1 |
| Asthenosphere | A hot, mobile layer of partially molten rock below the lithosphere. Because it can flow, the plates above it can move. | Page 14, Fig. 2.1 | Shown as about 200 km thick in Fig. 2.1 |
| Tectonic plate | A massive slab of solid rock that carries continents (continental), ocean floor (oceanic) or both (mixed), moving a few centimetres a year. | Pages 13–15, Fig. 2.3 | Indo-Australian Plate, Pacific Plate, Eurasian Plate |
| Convection current | The circulation set up in the mantle when hot material rises and cooler material sinks. It pushes and pulls the plates. | Page 15, Fig. 2.2 | Fig. 2.2 shows the loops, and magma zones under the crust |
| Convergent boundary | Where two plates move towards each other — crust is crumpled or destroyed. | Page 15 | The Himalaya, formed by colliding continental plates |
| Divergent boundary | Where two plates move apart; magma rises into the gap and makes new crust. | Page 15 | The Mid-Atlantic Ridge |
| Transform boundary | Where two plates slide past each other; no crust is made or destroyed, so earthquakes dominate. | Page 15 | The San Andreas Fault, United States |
| Ring of Fire | The belt around the Pacific Ocean where most of the world's earthquakes and volcanoes occur. | Page 16, Figs. 2.3 and 2.4 | The dense band of dots and triangles rimming the Pacific in Fig. 2.4 |
| Weathering | The breaking down of rock where it lies — physical, chemical or biological. The broken material does not move. | Pages 19–20, Fig. 2.8 | Plant roots growing into cracks and splitting a rock |
| Erosion | Wearing away and carrying away of soil and rock by water, wind, ice or waves. | Page 20, Fig. 2.9 | Gullies cut by running water; soil lifted by wind |
| Agents of gradation | The natural forces that wear down, transport and deposit material, levelling the surface over time. | Pages 21–22 | Running water, glaciers, wind, waves, groundwater |
| Karst topography | The landscape made where underground water dissolves limestone and other soluble rock. | Pages 31–32, Figs. 2.24–2.26 | Caves, stalactites, stalagmites, sinkholes, underground rivers |
Exercises
- Chapter opening — The Big Questions Page 13
- Fig. 2.3, world map showing major plates and their direction of movement — LET'S MAP Page 16
- Comparing the plate map (Fig. 2.3) with the earthquake and volcano map (Fig. 2.4) — LET'S EXPLORE Page 16
- The Ring of Fire in Fig. 2.4 — LET'S EXPLORE Page 17
- Does India have a risk of earthquakes? (Fig. 2.5) — LET'S EXPLORE Page 17
- The photograph in Fig. 2.6 — LET'S EXPLORE Page 18
- Erosion caused by (a) water and (b) wind — LET'S EXPLORE Page 21
- The Sundarbans delta (Fig. 2.13) — LET'S EXPLORE Page 25
- The Chamoli flood of February 2021 (Fig. 2.20) — THINK ABOUT IT Page 29
- Landforms around your school or home — LET'S EXPLORE Page 32
- Completing the disaster exercises on pages 33–36 — LET'S EXPLORE Page 32
- The chapter's recap points, expanded — Before we move on … Page 37
- End-of-chapter exercise — Questions and activities Page 37–38