South 고등학교 2학년 Earth System Science
Chapters: 3
1. Birth of Earth and a dynamic planet
Early atmosphere, ocean and life · Evolution of the Earth system · Plate motion and driving forces · Volcanism in the rock cycle · Seismic waves and Earth's interior
- Origin and Evolution of the Earth: From Dust Cloud to Living Planet – Early thinkers said the planets formed from a spinning cloud of gas around the young Sun (nebular hypothesis) or from matter pulled out of the Sun by a passing star. Today scientists explain the universe with the Big Bang: about 13.7 billion years ago everything began from one tiny point and it is still expanding. Stars formed from clumps of gas; planets formed from dust around the Sun. The Earth, about 4.6 billion years old, was hot and molten; heavy iron sank to make the core and lighter rock formed the crust. Gases from volcanoes made the early air, water vapour rained into oceans, and life began in the oceans about 3.8 billion years ago.
- Earth as a System: Spheres and Energy – Earth is like one big machine with five parts: rock (geosphere), water (hydrosphere), ice (cryosphere), air (atmosphere) and life (biosphere). The Sun powers it. Sunlight comes as many kinds of rays (the electromagnetic spectrum). The Sun heats Earth unevenly, and that makes winds, breezes and ocean currents. Water, carbon, nitrogen and oxygen move round and round between the spheres in cycles. Humans now change these cycles, so we must use Earth carefully.
- Distribution of Oceans and Continents: Drift, Spreading and Plates – In 1912 Alfred Wegener said all continents were once one landmass, Pangaea, surrounded by one ocean, Panthalassa, and that they drifted apart. Matching coastlines, rocks, fossils, glacier deposits and placer gold supported him, but he could not explain the force. Mapping the ocean floor showed ridges, plains and trenches; Harry Hess then proposed sea-floor spreading: new crust forms at mid-ocean ridges and old crust sinks at trenches. This led to plate tectonics: the lithosphere is broken into rigid plates that move on the soft asthenosphere and meet at divergent, convergent and transform boundaries. The Indian plate broke away from the south, moved north, and collided with Asia to raise the Himalayas.
- Rocks and Minerals – A mineral is a natural, non-living solid with a fixed chemical make-up and a regular crystal shape, like quartz or halite. A rock is a mixture of one or more minerals. Rocks are of three types: igneous (from cooled magma or lava), sedimentary (from layers of pressed bits) and metamorphic (changed by heat and pressure). The rock cycle slowly turns each type into the others over millions of years.
2. Ocean motion
Ekman transport and geostrophic currents · Ocean waves · Storm surges and tsunamis · Tides
- Ekman Transport and Geostrophic Currents – Wind drags the sea surface, and Earth's spin turns each water layer to the right (in the north). Added up, the water moves 90 degrees to the right of the wind: Ekman transport. This piles water into a low hill in an ocean basin. Water flowing round that hill, balanced by the spin of Earth, is a geostrophic current, the engine of the great ocean gyres.
- Natural Hazards – A natural hazard is a natural event that can harm people and property, such as an earthquake, volcano, landslide, flood, drought or cyclone. It becomes a disaster when it hits people who are not ready. Geological hazards come from inside the Earth; meteorological (weather) hazards come from the air and water. Risk = hazard × vulnerability ÷ capacity to cope, so warning systems, strong buildings and trained people cut the damage.
3. Precipitation and atmospheric motion
Selective absorption by gases · Heat budget of surface and air · Lapse rates and stability · Hydrostatic balance · Geostrophic and gradient winds · Planetary waves
- The Greenhouse Effect – The Sun heats Earth with visible light. About 30% is reflected straight back to space (albedo ≈ 0.30). The rest warms the ground, which gives off infrared radiation. Greenhouse gases – water vapour, carbon dioxide, methane, nitrous oxide – let visible light through but absorb infrared and send part of it back down. Earth settles at the temperature where energy in equals energy out. Without greenhouse gases Earth would average about −18 °C; with them it is about +15 °C. Adding more CO₂ and CH₄ (from burning fuels, farming, landfills) strengthens the effect and warms the planet.
- Atmospheric Stability and Adiabatic Processes – When a parcel of air rises, the pressure around it falls, so it expands and cools without gaining or losing heat: adiabatic cooling. Dry (unsaturated) air cools 10 °C per km (dry adiabatic lapse rate). After it reaches its dew point, vapour condenses into cloud and releases latent heat, so it cools only about 4 to 7 °C per km (saturated or moist adiabatic lapse rate, about 6). The surrounding air has its own environmental lapse rate (average 6.5 °C per km). If a rising parcel becomes colder than its surroundings, it is heavier and stops: stable air, flat clouds, fog and smog. If it stays warmer, it keeps rising: unstable air, tall cumulus and thunderstorms. Between the two rates the air is conditionally unstable. An inversion (air warmer higher up) is very stable.
- Atmospheric Pressure – Air has weight. The whole column of air above a surface pushes down on it; this push per square metre is atmospheric pressure. At sea level it is about 101 kPa (101 300 Pa), the same as a 760 mm column of mercury or about 10 m of water. Higher up there is less air above you, so pressure falls. In still air, the upward push of pressure on a layer balances the layer's weight (hydrostatic balance). Air flows from high pressure to low pressure, which is wind.
- Geostrophic and Gradient Wind – Air is pushed from high to low pressure by the pressure gradient force. Once it moves, Earth's spin (the Coriolis force) turns it. High above the ground the two forces balance and the wind blows along the isobars: the geostrophic wind. Around curved isobars the wind is the gradient wind.
- Atmospheric Circulation and Weather Systems – Air has weight, so it presses down: this is air pressure (about 1013 mb at sea level). Wind blows from high pressure to low pressure, pushed by the pressure gradient force, turned by the Coriolis force (right in the north, left in the south) and slowed by friction near the ground. Uneven heating makes pressure belts (equatorial low, subtropical highs, subpolar lows, polar highs) and three circulation cells, giving planetary winds: trade winds, westerlies and polar easterlies. Belts shift with the seasons, giving seasonal winds like the monsoon; local winds include land and sea breezes and mountain and valley winds. Big bodies of air with the same temperature and moisture are air masses; where two meet is a front. Cyclones are low-pressure storms: tropical cyclones form over warm seas; extratropical ones form along fronts. Thunderstorms and tornadoes are small but violent storms.