Earth Interior, Rocks, Earthquakes, Volcanoes and Landforms: Physical Geography Notes for SSC Exams

Physical geography questions on the structure of the earth, rocks, earthquakes, volcanoes and landforms are asked in every SSC exam. This guide on earth interior, rocks, earthquakes and landforms for SSC covers the layers of the earth, the three types of rocks and their examples, earthquakes and volcanoes, plate tectonics and the landforms made by rivers, glaciers, wind and sea, with practice questions and FAQs.

Structure of the Earth

• The boundary between the crust and mantle is the Mohorovicic (Moho) discontinuity; between the mantle and core the Gutenberg discontinuity; between the outer and the inner core the Lehmann discontinuity.
• The average radius of the earth is about 6,371 km.
• The most abundant elements of the crust are oxygen, silicon and aluminium.
• The most abundant element of the whole earth is iron.

Types of Rocks

Plate Tectonics and Continental Drift

• Alfred Wegener proposed the continental drift theory in 1912: all continents were once joined in a supercontinent Pangaea, surrounded by Panthalassa; it split into Laurasia and Gondwanaland.
• Plate tectonics divides the lithosphere into seven major plates (Pacific, North American, South American, African, Eurasian, Indo-Australian and Antarctic) and several minor ones.
• At divergent boundaries plates move apart (mid-oceanic ridges); at convergent boundaries they collide (mountains like the Himalayas, trenches); at transform boundaries they slide past each other (San Andreas Fault).
• The Himalayas formed by the collision of the Indian plate and the Eurasian plate.

Earthquakes

• The Ring of Fire around the Pacific has about 75% of the world’s volcanoes and the most earthquakes.
• The Himalayan belt and Andaman–Nicobar are the earthquake-prone areas of India; India has five seismic zones (II to V), with zone V being the most active.
• A tsunami is a large sea wave caused by an undersea earthquake; the Indian Ocean tsunami struck on 26 December 2004.

Volcanoes

• The molten rock inside the earth is magma; on the surface it is lava.
• Volcanic landforms include the cone, crater, caldera and lava plateaus such as the Deccan Plateau (formed by basaltic lava).
• Mount Kilimanjaro is the highest mountain in Africa; Mount Aconcagua in South America.

Weathering and Erosion

• Weathering is the breaking down of rocks in place (physical, chemical and biological); erosion is the removal of material by rivers, glaciers, wind and sea.
• Exfoliation is the peeling off of rock layers caused by heating and cooling.
• Chemical weathering is the most active in humid regions; limestone is dissolved to form karst landforms.

Landforms Made by Agents of Erosion

Tricks to Remember

• Marble from limestone, slate from shale, quartzite from sandstone, gneiss from granite.
• S waves do not pass through liquids; hence the outer core is liquid.
• Richter = magnitude; Mercalli = intensity; Seismograph = instrument.
• Stalactites hang from the roof (“c” for ceiling), stalagmites rise from the ground (“g” for ground).

Quick Tips

• Learn the pairs of original and metamorphic rocks.
• Remember that S waves cannot pass through liquids.
• Learn the three scales and instruments for earthquakes.
• Remember the examples of landforms with each agent.

Quick Revision Points

• Earth layers: crust, mantle, outer core, inner core.
• Igneous, sedimentary and metamorphic are the three rock types.
• Epicentre is on the surface; focus is inside.
• Richter scale measures magnitude.
• Barren Island is the only active volcano of India.

Practice Questions With Answers

1. Which is the thinnest layer of the earth?
   Answer: Crust
2. Marble is formed from which rock?
   Answer: Limestone
3. Which waves cannot pass through liquids?
   Answer: S waves
4. Which scale measures the magnitude of earthquakes?
   Answer: Richter scale
5. Which is the only active volcano in India?
   Answer: Barren Island (Andaman)
6. Who proposed the continental drift theory?
   Answer: Alfred Wegener
7. What is the supercontinent called?
   Answer: Pangaea
8. Which landform is formed by river deposition at its mouth?
   Answer: Delta
9. What is the point above the focus called?
   Answer: Epicentre
10. Which discontinuity separates the crust and the mantle?
    Answer: Moho discontinuity

How to Practise This Chapter

Practise 10 questions every day and write the steps on paper. Then attempt timed sets from our practice papers and the previous year papers page. See all topics on the Indian Geography notes page, read the previous topic Oceans, Straits and Ocean Currents and the next topic Atmosphere, Winds and Pressure Belts.

Frequently Asked Questions

What are the layers of the earth?

The crust, the mantle, the outer core and the inner core.

What are the three types of rocks?

Igneous, sedimentary and metamorphic.

Which rocks contain fossils?

Sedimentary rocks.

What is the epicentre?

The point on the earth’s surface directly above the focus of an earthquake.

What is a seismograph?

An instrument that records earthquake waves.

What do P and S waves mean?

Primary and secondary waves; P waves are faster, and S waves do not pass through liquids.

What is the Ring of Fire?

The belt of volcanoes and earthquakes around the Pacific Ocean.

What is plate tectonics?

The theory that the earth’s lithosphere is divided into moving plates.

What is weathering?

The breaking of rocks in place by physical, chemical and biological agents.

What is the difference between stalactites and stalagmites?

Stalactites hang from the cave roof and stalagmites rise from the floor.

Is this topic asked in SSC?

Yes. Physical geography is a regular topic.

What is magma?

The molten rock inside the earth.