Earth Structure
Geography · पृथ्वी की संरचना
📋Quick Overview
Earth is the 3rd planet from the Sun and the 5th largest planet. Its shape is not a perfect sphere — it is an oblate spheroid (slightly flattened at poles, bulging at equator), also called a GEOID. Earth has three main layers: Crust, Mantle, and Core. It rotates on its axis (rotation = day/night) and revolves around the Sun (revolution = seasons/year).
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Earth's age is approximately 4.54 billion years. It is the densest planet in the solar system.
📖Three Layers of Earth
| Layer | Depth | Composition | Key Facts |
|---|---|---|---|
| Crust (भूपर्पटी) | 0–70 km | Silica + Alumina (SiAl) on continents, Silica + Magnesium (SiMa) under oceans | Thinnest layer, we live on it, 2 types: Continental & Oceanic |
| Mantle (मैंटल) | 70–2,900 km | Silica + Magnesium (SiMa), semi-solid/plastic | Largest layer by volume, upper part = Asthenosphere (where tectonic plates float) |
| Core (कोर) | 2,900–6,371 km | Nickel + Iron (NiFe) | Outer core = liquid (creates magnetic field), Inner core = solid, hottest layer (~5,500°C) |
📝Discontinuities
| Discontinuity | Location | Separates |
|---|---|---|
| Mohorovicic (Moho) | ~35 km depth | Crust and Mantle |
| Gutenberg | ~2,900 km depth | Mantle and Outer Core |
| Lehmann | ~5,150 km depth | Outer Core and Inner Core |
📖Continental vs Oceanic Crust
📝Lithosphere & Asthenosphere
- •Lithosphere = Crust + uppermost solid part of Mantle (~100 km thick). Tectonic plates are part of the lithosphere.
- •Asthenosphere = Semi-molten, plastic-like layer below lithosphere (100–700 km). Plates float on it.
- •Convection currents in the asthenosphere cause tectonic plate movement.
📝Rotation vs Revolution
| Feature | Rotation | Revolution |
|---|---|---|
| Definition | Earth spinning on its own axis | Earth moving around the Sun |
| Time taken | 24 hours (1 day) | 365.25 days (1 year) |
| Direction | West to East | Counterclockwise (from North Pole view) |
| Causes | Day and Night, Time zones | Seasons, Leap year |
📝Important Lines & Circles
| Line/Circle | Position | Significance |
|---|---|---|
| Equator | 0° Latitude | Divides Earth into Northern & Southern Hemispheres. Longest latitude. |
| Tropic of Cancer | 23.5° N Latitude | Passes through 8 states of India (Gujarat, Rajasthan, MP, Chhattisgarh, Jharkhand, WB, Tripura, Mizoram) |
| Tropic of Capricorn | 23.5° S Latitude | Southern hemisphere counterpart of Tropic of Cancer |
| Prime Meridian (Greenwich) | 0° Longitude | Divides Earth into Eastern & Western Hemispheres. Passes through Greenwich, London. |
| International Date Line (IDL) | ~180° Longitude | Crossing it changes the date: +1 day (west to east), -1 day (east to west). Not a straight line — zigzags to avoid land. |
| Indian Standard Meridian | 82.5° E Longitude | Passes through Mirzapur (UP). IST = GMT + 5:30 |