Physical Geography

1. THE EARTH AND THE UNIVERSE

Universe

• The Universe comprises all of space, time, matter, and energy. Estimated to be about 13.8 billion years old.
• Our galaxy is the Milky Way, a barred spiral galaxy with over 100 billion stars.

Solar System

• The Solar System consists of the Sun, 8 planets, 5 recognized dwarf planets, and over 170 moons.
• The planets in order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
• Earth is the third planet from the Sun and is shaped like an oblate spheroid (flattened at the poles).
• Perihelion (closest to the Sun): January 3 (~147 million km)
• Aphelion (farthest from the Sun): July 4 (~152 million km)

Motions of Earth

• Rotation: Earth spins on its axis from west to east. One rotation = 23 hrs 56 min. Causes day and night.
• Revolution: Earth's orbit around the Sun takes 365.25 days. Leads to formation of a year.
• Tilt of Axis: 23.5° tilt responsible for seasonal changes.
• Equinoxes (equal day and night): March 21 (Spring) and September 23 (Autumn)
• Solstices: June 21 (longest day in Northern Hemisphere), December 22 (shortest day)

2. INTERIOR OF THE EARTH

Structure

• Earth has a layered structure: Crust, Mantle, Core.

Crust

• Outermost layer, 5–70 km thick.
• Continental crust: Made of granite, thicker (~35 km).
• Oceanic crust: Made of basalt, thinner (~5–10 km).

Mantle

• Extends from the base of the crust to about 2900 km.
• Composed mainly of silicate rocks rich in iron and magnesium.

Core

• Innermost layer, extends to ~6371 km.
• Divided into liquid outer core and solid inner core.
• Composed mainly of iron and nickel (NIFE).

Seismic Waves

• P-waves (Primary): Fastest, travel through solids and liquids.
• S-waves (Secondary): Travel only through solids.
• Surface waves: Travel on Earth's surface, most destructive.

Discontinuities

• Moho: Crust-Mantle boundary.
• Gutenberg: Mantle-Core boundary.
• Lehmann: Outer Core-Inner Core boundary.

3. ROCKS & MINERALS

Types of Rocks

• Igneous: Formed from solidification of magma/lava.
• • Intrusive: Granite; Extrusive: Basalt
• Sedimentary: Formed by deposition and compaction of sediments.
• • Sandstone, limestone
• Metamorphic: Formed by transformation of existing rocks due to heat/pressure.
• • Marble (from limestone), Slate (from shale)

Rock Cycle

• Igneous → Weathering → Sediments → Sedimentary → Heat/Pressure → Metamorphic → Melts → Magma → Igneous

4. GEOMORPHIC PROCESSES

Exogenic Processes

• Operate on Earth’s surface.
• Weathering: Breakdown of rocks in situ. Types:
• • Mechanical (freeze-thaw), Chemical (oxidation), Biological (root action)
• Erosion: Removal of weathered material by wind, water, ice.
• Mass wasting: Downslope movement due to gravity, e.g., landslides.

Endogenic Processes

• Originate within Earth.
• Volcanism: Emission of magma onto the surface.
• • Active (Etna), Dormant (Kilimanjaro), Extinct (Deccan Traps)
• Earthquakes: Sudden shaking of Earth’s crust.
• • Focus: Point of origin; Epicenter: Point on surface above focus.
  • Measured by Richter Scale (magnitude), Mercalli Scale (intensity)

Landforms

• Fluvial: V-shaped valleys, meanders, oxbow lakes (formed by rivers)
• Aeolian: Sand dunes, loess deposits (wind action)
• Glacial: U-shaped valleys, moraines (glacial action)
• Karst: Caves, stalactites, stalagmites (limestone dissolution)

5. LANDFORMS AND THEIR EVOLUTION

Fluvial Landforms (Rivers)

• Youth Stage: V-shaped valleys, waterfalls, rapids.
• Mature Stage: Meanders, floodplains.
• Old Stage: Oxbow lakes, deltas.
• River Capture: Occurs when a river diverts the flow of another.

🔹 Example: Ganga-Brahmaputra delta — world’s largest delta.

Glacial Landforms

• Found in high latitudes and mountains.
• Erosional: Cirques, aretes, horns, U-shaped valleys.
• Depositional: Moraines (lateral, medial, terminal), drumlins.

🔹 Example: Gangotri Glacier (Uttarakhand).

Aeolian Landforms (Wind)

• Dominant in deserts.
• Erosional: Mushroom rocks, deflation hollows.
• Depositional: Sand dunes (barchans, seif), loess.

🔹 Example: Thar Desert (India) features extensive barchans.

Karst Landforms (Limestone regions)

• Formed by chemical weathering (carbonation).
• Erosional: Caves, sinkholes, swallow holes.
• Depositional: Stalactites (ceiling), stalagmites (ground).

🔹 Example: Karst topography in Meghalaya (Cherrapunji).

6. CLIMATOLOGY

Atmosphere Composition

• Nitrogen (78%), Oxygen (21%), Argon (0.93%), CO₂ (0.04%)
• Layers (Bottom to Top): Troposphere → Stratosphere → Mesosphere → Thermosphere → Exosphere.

🔹 Tropopause height: ~8 km (poles), ~18 km (equator)

Solar Radiation

• Insolation: Solar energy received on Earth.
• Affected by latitude, season, and time of day.
• Albedo: Reflectivity; Ice = high albedo, Forest = low albedo.

Heat Budget of Earth

• Incoming solar radiation (100%) → Reflected (35%), Absorbed (65%).
• Earth emits long-wave (infrared) radiation.

Temperature Distribution

• Isotherms: Lines joining equal temperature.
• Influencing factors: Latitude, altitude, ocean currents, wind, cloud cover.

🔹 Example: Western coastal India is warmer in winter than interior due to maritime influence.

Pressure Belts

• Equatorial Low (Doldrums) → Subtropical High → Subpolar Low → Polar High.
• Shift with seasons — known as apparent movement of the Sun.

Winds

• Planetary Winds: Trade Winds, Westerlies, Polar Easterlies.
• Local Winds: Loo (hot), Chinook (warm), Mistral (cold).
• Jet Streams: High-speed winds in upper troposphere.

Cyclones

• Tropical Cyclones: Low-pressure systems, form over warm oceans.
• • Known as hurricanes (USA), typhoons (Asia), cyclones (India).
  • Eye: Calm center.
• Temperate Cyclones: Form along fronts, mid-latitudes, associated with westerlies.

🔹 Example: Cyclone Fani (2019) — major cyclone in Odisha.

7. OCEANOGRAPHY

Ocean Relief

• Continental Shelf → Continental Slope → Abyssal Plain → Oceanic Ridge.
• Mid-Ocean Ridge: Underwater mountain system, site of sea-floor spreading.

Ocean Currents

• Caused by wind, Coriolis force, temperature, salinity.
• Warm Currents: Gulf Stream, Kuroshio
• Cold Currents: Labrador, Benguela

🔹 Example: Peru Current causes aridity of Atacama Desert.

Tides

• Caused by gravitational pull of Moon and Sun.
• Spring Tide: New and Full Moon (high tides).
• Neap Tide: First and Third Quarter (low variation).

El Niño and La Niña

• El Niño: Warming of central Pacific Ocean → Weak monsoon in India.
• La Niña: Cooling → Stronger monsoon.

🔹 ENSO (El Niño-Southern Oscillation): Combined ocean-atmosphere phenomenon.

8. BIOGEOGRAPHY

Soil Formation

• Weathering + Organic material.
• Factors: Parent rock, climate, organisms, relief, time.

Soil Types in India

• Alluvial: Fertile, found in Indo-Gangetic plain.
• Black (Regur): Cotton cultivation, Deccan plateau.
• Red: Iron-rich, found in Chotanagpur.
• Laterite: Leached, poor fertility.
• Desert: Sandy, poor in humus.
• Mountain soils: Organic-rich, hilly regions.

Natural Vegetation Types

• Tropical Evergreen: High rainfall, Western Ghats, NE India.
• Tropical Deciduous: Monsoon forests, central India.
• Thorn Forests: Rajasthan.
• Montane: Himalayan region.
• Mangroves: Coastal regions (Sundarbans).