Grade 7 Exam > Grade 7 Notes > Social Studies > Cheatsheet: Physical Geography
Cheatsheet: Physical Geography
1. Earth's Structure and Composition
1.1 Layers of the Earth
| Layer | Key Characteristics |
|---|---|
| Crust | Outermost solid layer; 5-70 km thick; composed of rocks and minerals |
| Mantle | Thickest layer beneath crust; about 2,900 km thick; semi-solid rock that flows slowly |
| Outer Core | Liquid layer composed of iron and nickel; about 2,300 km thick |
| Inner Core | Solid sphere at Earth's center; extremely hot (5,000°C); made of iron and nickel |
1.2 Types of Crust
| Type | Description |
|---|---|
| Continental Crust | Thicker (30-70 km); less dense; forms continents; mostly granite |
| Oceanic Crust | Thinner (5-10 km); more dense; forms ocean floors; mostly basalt |
2. Landforms and Their Formation
2.1 Major Landforms
| Landform | Definition |
|---|---|
| Mountain | Large natural elevation of earth's surface with steep sides; rises above 600 meters |
| Plateau | Elevated flat area of land raised above surrounding area on at least one side |
| Plain | Large area of flat or gently rolling land with low relief |
| Valley | Low area between hills or mountains, often with a river running through it |
| Canyon | Deep, narrow valley with steep sides carved by a river |
| Hill | Rounded elevation of land lower than a mountain; less than 600 meters high |
2.2 Types of Mountains
| Type | Formation Process |
|---|---|
| Fold Mountains | Formed when tectonic plates collide and rock layers fold upward (e.g., Himalayas, Rockies) |
| Block Mountains | Formed when large blocks of earth are broken and displaced by faults (e.g., Sierra Nevada) |
| Volcanic Mountains | Formed when molten rock erupts and builds up on Earth's surface (e.g., Mount Fuji) |
| Dome Mountains | Formed when magma pushes up rock layers but doesn't break through the surface |
3. Plate Tectonics
3.1 Tectonic Plates
- Earth's lithosphere is divided into large pieces called tectonic plates
- Plates float on the semi-liquid asthenosphere (upper mantle)
- There are 7 major plates and many minor plates
- Plates move very slowly (2-10 cm per year)
3.2 Types of Plate Boundaries
| Boundary Type | Movement & Results |
|---|---|
| Convergent | Plates move toward each other; creates mountains, trenches, and volcanoes |
| Divergent | Plates move apart; creates new crust, mid-ocean ridges, rift valleys |
| Transform | Plates slide past each other; causes earthquakes (e.g., San Andreas Fault) |
3.3 Effects of Plate Movement
- Earthquakes: sudden movement of plates releases energy
- Volcanoes: magma rises through cracks in Earth's crust
- Mountain formation: collision of plates pushes rock upward
- Ocean trenches: oceanic plate subducts beneath another plate
- Continental drift: continents slowly change position over millions of years
4. Weathering and Erosion
4.1 Weathering
| Type | Description & Examples |
|---|---|
| Physical Weathering | Breaking down rocks without changing chemical composition; freeze-thaw, heating-cooling, plant roots |
| Chemical Weathering | Breaking down rocks through chemical reactions; oxidation, acid rain, carbonation |
| Biological Weathering | Breaking down rocks by living organisms; plant roots, burrowing animals, lichens |
4.2 Erosion
- Process of moving weathered rock and soil from one place to another
- Main agents: water, wind, ice, gravity
| Agent | How It Works |
|---|---|
| Water | Rivers and streams carry sediment; creates valleys, canyons, deltas |
| Wind | Picks up and moves small particles; forms sand dunes, shapes desert rocks |
| Ice (Glaciers) | Moving ice scrapes and carries rock; forms U-shaped valleys, fjords |
| Gravity | Pulls materials downslope; causes landslides, rockfalls, mudslides |
4.3 Deposition
- Process where eroded materials are dropped in a new location
- Creates landforms: deltas, sand dunes, moraines, alluvial fans
- Occurs when erosion agents lose energy and can no longer carry sediment
5. Water Bodies
5.1 Oceans
- Cover about 71% of Earth's surface
- Five major oceans: Pacific (largest), Atlantic, Indian, Southern, Arctic (smallest)
- Average depth: 3,800 meters; deepest point: Mariana Trench (11,000 meters)
- Contains salt water (average salinity 3.5%)
5.2 Freshwater Bodies
| Water Body | Description |
|---|---|
| River | Natural flowing water that moves from higher to lower elevation; flows to ocean, lake, or another river |
| Lake | Large body of water surrounded by land; can be freshwater or saltwater |
| Stream/Creek | Small flowing body of water; smaller than a river |
| Pond | Small body of still water; smaller and shallower than a lake |
| Glacier | Large mass of ice that moves slowly over land; stores freshwater in frozen form |
5.3 River Systems
- Source: where a river begins (spring, lake, or melting snow)
- Tributary: smaller stream or river that flows into a larger river
- Mouth: where a river ends (flows into ocean, sea, or lake)
- Delta: triangular deposit of sediment at river mouth
- Drainage basin/Watershed: area of land drained by a river and its tributaries
6. Climate and Weather
6.1 Weather vs. Climate
| Term | Definition |
|---|---|
| Weather | Day-to-day conditions of the atmosphere (temperature, precipitation, wind, humidity) |
| Climate | Average weather patterns in a region over a long period (30+ years) |
6.2 Elements of Weather and Climate
- Temperature: measure of how hot or cold the air is
- Precipitation: water falling from the sky (rain, snow, sleet, hail)
- Humidity: amount of water vapor in the air
- Air pressure: weight of air pressing down on Earth's surface
- Wind: movement of air from high pressure to low pressure areas
- Cloud cover: amount of sky covered by clouds
6.3 Factors Affecting Climate
| Factor | Effect on Climate |
|---|---|
| Latitude | Distance from equator; equator is hot, poles are cold |
| Altitude | Height above sea level; higher altitude = cooler temperatures |
| Distance from Water | Coastal areas have milder climates; inland areas have extreme temperatures |
| Ocean Currents | Warm currents raise temperature; cold currents lower temperature |
| Wind Patterns | Prevailing winds bring moisture or dryness to regions |
| Mountain Ranges | Block wind and moisture; create rain shadows on leeward side |
7. Climate Zones
7.1 Major Climate Zones
| Climate Zone | Characteristics |
|---|---|
| Tropical | Hot and wet year-round; near equator; rainforests and savannas |
| Dry/Arid | Very little rainfall; hot days, cool nights; deserts and semi-arid regions |
| Temperate | Moderate temperatures; four distinct seasons; between tropics and polar regions |
| Continental | Hot summers, cold winters; large temperature range; inland areas |
| Polar | Very cold year-round; little precipitation; near North and South Poles |
7.2 Precipitation Patterns
- Rain shadow: dry area on leeward side of mountain range
- Monsoons: seasonal winds that bring heavy rainfall (common in South Asia)
- Convectional rainfall: warm air rises, cools, and releases moisture
- Orographic rainfall: moist air rises over mountains, cools, and releases precipitation
8. Natural Resources
8.1 Types of Natural Resources
| Type | Description & Examples |
|---|---|
| Renewable | Can be replaced naturally; solar energy, wind, water, forests, soil |
| Non-renewable | Cannot be replaced once used; fossil fuels (coal, oil, natural gas), minerals, metals |
8.2 Water Resources
- Only 3% of Earth's water is freshwater
- Most freshwater is frozen in glaciers and ice caps
- Less than 1% of freshwater is available for human use
- Sources: rivers, lakes, groundwater (aquifers), precipitation
8.3 Soil as a Resource
- Forms from weathered rock and decomposed organic matter
- Takes hundreds to thousands of years to form
- Essential for agriculture and plant growth
- Can be depleted by overuse, erosion, and pollution
9. Environmental Issues
9.1 Deforestation
- Clearing forests for agriculture, logging, or development
- Effects: loss of habitat, soil erosion, climate change, reduced oxygen production
- Major areas affected: Amazon rainforest, Southeast Asia, Central Africa
9.2 Desertification
- Process where fertile land becomes desert
- Causes: overgrazing, deforestation, poor farming practices, climate change
- Results in loss of farmland and food shortages
9.3 Water Pollution
- Contamination of water bodies by harmful substances
- Sources: industrial waste, sewage, agricultural runoff, oil spills
- Affects drinking water, aquatic life, and human health
9.4 Soil Erosion
- Removal of topsoil by wind, water, or human activity
- Causes: deforestation, overgrazing, poor farming methods
- Reduces soil fertility and agricultural productivity
10. Maps and Geographic Tools
10.1 Types of Maps
| Map Type | Purpose |
|---|---|
| Physical Map | Shows natural features (mountains, rivers, elevation, landforms) |
| Political Map | Shows boundaries, cities, countries, states |
| Climate Map | Shows climate zones and weather patterns |
| Topographic Map | Shows elevation using contour lines; detailed terrain features |
| Resource Map | Shows location of natural resources (minerals, forests, water) |
10.2 Map Elements
- Title: tells what the map shows
- Legend/Key: explains symbols and colors used
- Scale: shows relationship between distance on map and actual distance
- Compass rose: shows cardinal directions (N, S, E, W)
- Grid: system of lines (latitude and longitude) to locate places
10.3 Latitude and Longitude
| Term | Definition |
|---|---|
| Latitude | Horizontal lines measuring distance north or south of equator (0°); range 0-90° |
| Longitude | Vertical lines measuring distance east or west of Prime Meridian (0°); range 0-180° |
| Equator | 0° latitude; divides Earth into Northern and Southern Hemispheres |
| Prime Meridian | 0° longitude; divides Earth into Eastern and Western Hemispheres |
10.4 Important Lines of Latitude
- Equator: 0°
- Tropic of Cancer: 23.5°N
- Tropic of Capricorn: 23.5°S
- Arctic Circle: 66.5°N
- Antarctic Circle: 66.5°S
11. Continents and Oceans
11.1 Seven Continents
| Continent | Key Features |
|---|---|
| Asia | Largest continent; highest mountains (Himalayas); most populous |
| Africa | Second largest; Sahara Desert; equator runs through center |
| North America | Rocky Mountains; Great Lakes; connected to South America |
| South America | Amazon rainforest; Andes Mountains; Amazon River |
| Antarctica | Southernmost continent; covered in ice; coldest place on Earth |
| Europe | Second smallest; highly developed; many countries |
| Australia | Smallest continent; also a country; surrounded by water |
11.2 Five Major Oceans
- Pacific Ocean: largest and deepest ocean
- Atlantic Ocean: second largest; separates Americas from Europe and Africa
- Indian Ocean: third largest; located south of Asia
- Southern Ocean: surrounds Antarctica
- Arctic Ocean: smallest; located around North Pole; mostly frozen
12. The Atmosphere
12.1 Layers of the Atmosphere
| Layer | Characteristics |
|---|---|
| Troposphere | Lowest layer (0-12 km); weather occurs here; temperature decreases with altitude |
| Stratosphere | 12-50 km; contains ozone layer; protects from UV radiation |
| Mesosphere | 50-80 km; coldest layer; meteors burn up here |
| Thermosphere | 80-600 km; very hot; auroras occur here |
12.2 Composition of Air
- Nitrogen: 78%
- Oxygen: 21%
- Other gases (carbon dioxide, water vapor, argon): 1%
13. Rock Cycle
13.1 Three Types of Rocks
| Rock Type | Formation Process & Examples |
|---|---|
| Igneous | Forms from cooled and hardened magma or lava; granite, basalt, obsidian |
| Sedimentary | Forms from compressed layers of sediment; sandstone, limestone, shale |
| Metamorphic | Forms when existing rocks change due to heat and pressure; marble, slate, quartzite |
13.2 Rock Cycle Process
- Rocks continuously change from one type to another over millions of years
- Processes: melting, cooling, weathering, erosion, compaction, heat, pressure
- Any rock type can transform into any other rock type
14. Volcanoes and Earthquakes
14.1 Volcano Formation
- Opening in Earth's crust where magma erupts to the surface
- Form at convergent boundaries (subduction) and divergent boundaries
- Ring of Fire: area around Pacific Ocean with many active volcanoes
14.2 Parts of a Volcano
- Magma chamber: underground pool of molten rock
- Vent: opening through which lava erupts
- Crater: bowl-shaped depression at top of volcano
- Lava: magma that reaches Earth's surface
14.3 Earthquakes
- Sudden shaking of ground caused by movement along faults
- Focus/Hypocenter: point underground where earthquake starts
- Epicenter: point on surface directly above focus
- Measured using Richter scale or moment magnitude scale
- Seismograph: instrument that records earthquake waves
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