Our Changing Earth
Overview
Earth is never still — its surface is divided into pieces (plates) that slowly keep moving, causing earthquakes and volcanoes. And from outside, wind, water, and ice wear the land down (weathering, erosion) and deposit material in new places (deposition). Let us explore this.
Typed Notes
Plates and Their Movement
Earth's crust is not one single piece — it is divided into 7 major and several smaller plates (like puzzle pieces). These plates float on the soft, hot rock of the mantle — moving 1–2 cm every year! This movement comes from endogenic forces (heat from inside the Earth). Where plates meet — mountains are formed (Himalayas), earthquakes occur, and volcanoes erupt. Plate boundaries are the most active zones on Earth.
Earthquake — The Shaking of the Ground
When plates suddenly shift — the ground shakes — this is an earthquake. The point where it originates inside the Earth is called the focus. The point directly above the focus on the surface is called the epicentre — this is where the shaking and damage are greatest. The instrument used to measure earthquakes is the seismograph; its readings give the strength (magnitude) of the earthquake. When an earthquake occurs under the ocean, it creates a massive wave in the ocean water — a tsunami. Japan (2011) and India's Andaman Islands (2004) suffered great damage from tsunamis.
Weathering and Erosion
Weathering — the breaking down of land in its own place: physical (rocks cracking due to heat and cold, water freezing), chemical (rocks dissolving or changing due to water), biological (plant roots splitting rocks, insects). Erosion — the carrying away of the broken material: rivers, wind, the sea, and glaciers all pick up material along their path and transport it. Together, these two processes change the land — mountains are worn down and plains are formed.
Landforms — What Forms Where
Rivers: waterfalls upstream (Jog Falls), gorges (deep valleys), meanders (winding paths) in the middle, and deltas at the mouth (Sundarbans). Wind (in deserts): sand dunes (mounds of sand), mushroom rocks (umbrella-shaped). Sea coasts: sea caves, sea arches, beaches. Glaciers: as ice moves, it leaves behind debris — moraines (heaps of rocks and soil). Each agent (river, wind, sea, ice) creates its own type of landforms in its region.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Earth's surface is divided into 7 major plates (and several smaller ones) — these slowly move (cm/year). This movement comes from endogenic forces — heat from inside the Earth.
- 02Earthquake: the sudden movement of plates. The point of origin = focus (underground), the point directly above it = epicentre (maximum damage). The instrument used to measure it = seismograph.
- 03Weathering: the breaking down of land — physical (heat and cold), chemical (dissolving and changing due to water), biological (plants and insects). Erosion: carrying away the broken material — by rivers, wind, sea, and glaciers.
- 04Landforms made by RIVERS: waterfall, gorge, meander, delta (at the mouth); by WIND: sand dunes (mounds of sand in deserts), mushroom rocks; by the SEA: sea caves, arches, beaches; by GLACIERS: moraines (debris carried along with ice).
- 05Volcano: when magma bursts out — lava, ash, gas. Active / dormant / extinct.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What is the difference between focus and epicentre?
What does a seismograph do?
What is the difference between weathering and erosion?
How are sand dunes formed?
How does a tsunami occur?
What are moraines?
Earth's 7 plates slowly move due to endogenic forces — earthquakes (focus, epicentre, seismograph) and volcanoes are caused by this. From outside: weathering (breaking down) + erosion (carrying away) allow rivers, wind, the sea, and glaciers to create landforms — waterfalls, deltas, dunes, caves, and moraines.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Which instrument measures the strength of an earthquake?
Q2.What is the underground origin point of an earthquake called?
Q3.What are the mounds of sand in a desert called?
Q4.What causes the movement of tectonic plates?
Mark karo — dashboard par progress dikhega.