The Earth Notes with PDF

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Geography: Core Concepts

Earth’s Coordinate System: Latitude & Longitude

• Latitude (φ)
  • Definition: Lines measuring distance north or south of the Equator.
  • Key Points:
    • Equator: 0° latitude
    • North Pole: 90° North latitude
    • South Pole: 90° South latitude
    • Latitudes beyond 90° North or South are impossible.
• Longitude
  • Definition: Lines measuring distance east or west of the Prime Meridian.
  • Key Point: Prime Meridian: 0° longitude.
• The Global Grid
  • The intersection of the Equator (0°N) and the Prime Meridian (0°E) is located in the Gulf of Guinea, Atlantic Ocean.

Great Circles

• Definition: Any circle that divides the Earth into two equal halves.
• Examples:
  • The Equator
  • All lines of longitude (meridians)
• Not a Great Circle: Any line of latitude other than the Equator (e.g., 60°N) is a smaller circle.

Locating Places & Antipodes

• Determining Northernmost/Southernmost Position: The location with the highest numerical value for its northern latitude is the farthest north.
  • Example: Among Beijing, New Delhi, New York, and Rome, Rome (41°54’N) is the farthest north.
• Finding the Antipode (exact opposite point on Earth):
  1. Latitude: Reverse the hemisphere (North becomes South).
  2. Longitude: Subtract the original longitude from 180° (East becomes West).
  • Example: The antipode of 30°N, 50°E is 30°S, 130°W.

Geographical Extremes

• Longest North-South Extension: Chile (approx. 17°S to 56°S).
• Regional Location: The coordinates 50°N, 50°E are located in Europe (near Belgium).

Time Zones and Longitude

Longitude and Time Calculation

• Basic Principle:
  • Earth rotates 360° in 24 hours → 15° per hour.
  • Therefore, 1° of longitude = 4 minutes of time difference.
• Calculating Longitude from Time:
  • 2 hours ahead of GMT = 30° East (e.g., Cairo).
  • 5 hours ahead of GMT = 75° East.
  • 3 hours ahead of GMT = 45° East.
  • 90° longitude difference = 6-hour time difference.
• Calculating Time from Longitude:
  • Noon at 82°30’E = 6:30 AM at Greenwich (0°).
  • A telegram sent from Greenwich at noon, received at 6:00 PM (with a 12-min delay), means the location is 87° East.

The Prime Meridian (0° Longitude)

• Definition: The line of 0° longitude, passing through Greenwich, England. Basis for Greenwich Mean Time (GMT).
• Countries it Passes Through: United Kingdom, France, Spain, Algeria, Mali, Burkina Faso, Togo, Ghana.
• Countries it Does Not Pass Through: Niger, Nigeria, Portugal.
• Capital Cities on GMT: London (UK), Lisbon (Portugal), Accra (Ghana), Dublin (Ireland).
  • Not on GMT: Addis Ababa, Ethiopia (2 hours 36 minutes ahead).

The International Date Line (IDL)

• Location: Approximately along the 180° meridian, primarily in the Pacific Ocean. It is not straight and is adjusted to avoid land masses.
• Time Difference from Greenwich: 12 hours.
• Crossing the Date Line:
  • East to West (America to Asia): Add one day.
  • West to East (Asia to America): Subtract one day.

Indian Standard Time (IST)

• Reference Meridian: 82°30’E.
• Difference from GMT: 5 hours 30 minutes ahead (GMT +5:30).
• Application: When it is noon at the IST meridian, it is 6:30 AM at Greenwich.
• First Sunrise in India (New Millennium): Seen on Katchal Island (~93°30’E).

Key Latitudinal Lines

The Equator (0° Latitude)

• Characteristics:
  • Divides Earth into Northern and Southern Hemispheres.
  • Length: ~40,000 km (24,901 miles).
  • 78.7% over water; 21.3% over land.
• Countries it Passes Through (13 countries): Brazil, Colombia, Democratic Republic of the Congo, Ecuador, Gabon, Indonesia, Kenya, Kiribati, Republic of the Congo, Sao Tome and Principe, Somalia, Uganda.
  • Does not pass through: Mexico, Venezuela, Equatorial Guinea, Rwanda, Brunei.
• Climatic Significance:
  • Minimum annual temperature range due to consistent sunlight.
  • Location of the Intertropical Convergence Zone (ITCZ).
• Comparative Geography:
  • The Equator, Tropic of Cancer, and Tropic of Capricorn all pass through Africa.
  • Singapore is the city nearest to the Equator from common options.

The Tropic of Cancer (23.5° N)

• Astronomical Fact: On the Winter Solstice (Dec 21/22), the noon sun altitude at the Tropic of Cancer is 43.0°.
• Location: 23° 30′ North.
• Nearest Indian City: Jabalpur (23° 11′ N). Also near Ahmedabad and Ujjain.
• Countries it Passes Through: India, Bangladesh, Myanmar, Saudi Arabia, UAE, Oman, China, Taiwan, Mexico, Bahamas, Egypt, Libya, Algeria, Mauritania, Mali, Niger, Chad.
  • Does not pass through: Iran.

The Tropic of Capricorn (23.5° S)

• Countries it Passes Through: Chile, Argentina, Paraguay, Brazil, Namibia, Botswana, South Africa, Madagascar, Mozambique, Australia.
  • Does not pass through: Bolivia.
• Meteorological Impact on India: When the sun is overhead here (Dec 21/22), high pressure develops over North-West India.

Earth’s Motion: Days, Nights, and Seasons

• Equinox
  • When: March 21 (Vernal) and September 23 (Autumnal).
  • Condition: Day and night are of equal duration (~12 hours each).
  • Sun Overhead At: The Equator.
• Summer Solstice (Northern Hemisphere)
  • When: Around June 20/21.
  • Condition: Longest day in the Northern Hemisphere.
  • Sun Overhead At: The Tropic of Cancer.
  • Effects: Smallest noon shadow; 24-hour daylight at the Arctic Circle.
• Winter Solstice (Northern Hemisphere)
  • When: Around December 21/22.
  • Condition: Shortest day in the Northern Hemisphere (longest day in the Southern Hemisphere).
  • Sun Overhead At: The Tropic of Capricorn.

Earth’s History and Geology

Origin and Age of the Earth

• Theories of Origin:
  • O. Schmidt: Earth originated from gases and dust.
  • James Jeans: Proposed the “Tidal Theory.”
  • F. Hoyle & Littleton: Proposed the “Nova Hypothesis.”
• Determining Age: Primary method is Uranium dating.

Geological History & Evolution of Life

• Geological Time Scale:
  • Pleistocene Epoch: The “Great Ice Age” (began over a million years ago).
  • “Little Ice Age”: A colder period from 1650 A.D. to 1870 A.D.
• Age of Dinosaurs: Lived approximately 208 to 144 million years ago.
• Chronological Order of Life Forms:
  1. Shelled animals
  2. First insects
  3. First reptiles
  4. First mammals
• First Fossil Evidence: Dates to the Archean Age (~3.5 billion years ago).
• Factors Influencing Evolution: Continental drift and glacial cycles.

Plate Tectonics and Continental Drift

• Supercontinents:
  • Pangea: The original single huge landmass, surrounded by the ocean Panthalassa.
  • It split into:
    • Laurasia (north)
    • Gondwanaland (south)
• Composition of Gondwanaland: South America, Africa, Australia, Antarctica, Madagascar, Arabian Peninsula, Indian Subcontinent.
  • Not part of Gondwanaland: North America (part of Laurasia).
• Mechanism of Drift: Primarily due to tectonic activities (movement of plates).
• Specific Plates: The Cocos Plate is located between Central America and the Pacific Plate.

Geological Forces and Changes

• Types of Forces:
  • Orogenic forces: Cause folding (bending of rock layers) and mountain-building.
  • Epeirogenic forces: Cause large-scale vertical movements of continents.
• Causes of Dynamic Changes: A combination of:
  • Endogenic Forces: Geothermal energy, plate movements, gravitational force.
  • External & Astronomical Factors: Electromagnetic radiation, Earth’s rotation and revolution.

Know More About The Earth:

• The Earth – Old Year Questions
• The Earth One Liner Questions & Answers