South 고등학교 3학년 Earth Science II

Chapters: 7

1. Earth's formation and fields

Formation of Earth · Internal energy · Interior from seismic waves · Standard gravity · Geomagnetism

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.
Interior of the Earth: Earthquake Waves, Layers and Volcanoes – Nobody can dig to the centre of the Earth, so we learn about the inside from direct sources (mine rocks, deep drilling, lava) and indirect sources (heat and pressure with depth, meteors, gravity, magnetism and, above all, earthquake waves). P-waves travel through solids and liquids; S-waves only through solids. Where the waves do not arrive, we get shadow zones, which prove the outer core is liquid. Earthquakes are measured by magnitude (Richter) and intensity (Mercalli). The Earth has a thin crust, a thick mantle with a soft asthenosphere, a liquid outer core and a solid inner core. Magma that reaches the surface builds volcanoes; magma that cools inside forms intrusive landforms like batholiths, sills and dykes.
Gravity – Gravity is the pull between all masses. Earth pulls every object towards its centre. A freely falling object speeds up by about 9.8 m/s every second (g), and this does not depend on its mass. Weight is the pull on your mass, W = m × g, so it changes from world to world while mass does not. A ball thrown sideways fast enough keeps missing the Earth and goes into orbit (about 7.9 km/s); at about 11.2 km/s it escapes.
Earth’s Magnetic Field (Geomagnetism) – Earth has a magnetic field like a tilted bar magnet. It is made by moving liquid iron in the outer core (the dynamo). A compass lines up with it. The angle between magnetic and true north is declination; the angle the field makes with the ground is dip (0° at the equator, 90° at the magnetic poles). The field forms a shield, the magnetosphere, that bends the solar wind. Some particles slip in near the poles and make the aurora.

2. Earth materials and resources

Silicate minerals · Polarising microscope · Forming mineral deposits · Minerals in daily life · Ocean resources

Silicate Minerals: How One Tiny Brick Builds Most of the Earth's Crust – Silicate minerals are minerals built from silicon and oxygen. Their basic brick is the SiO₄ tetrahedron: one silicon atom with four oxygen atoms around it. Tetrahedra can stay alone or share oxygens to form chains, sheets or a 3D framework. The way they link decides the mineral's shape, cleavage and hardness. Silicates make up over 90% of the Earth's crust.
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.
Natural Resources – Natural resources are useful things we take from nature: sunlight, wind, water, soil, forests, minerals, oil, gas and coal. Renewable resources come back in a human lifetime; non-renewable ones took millions of years to form and run out when used. Resources are spread unevenly because they form only where certain geological processes happened in the past (old seas, volcanoes, mountain building). Using them brings benefits such as energy, jobs and materials, but also costs such as pollution, habitat loss and hazards, so societies weigh costs against benefits and try to use them sustainably.

3. Geology of the Korean Peninsula

Reading geological maps · Geological history from data · Structural features · Precambrian basement

Geological Maps: Reading Rocks from Above – A geological map shows which rock is found at the ground surface, using colours and symbols. Rock layers (strata) form one on top of another, so lower layers are usually older (law of superposition). Tilted layers are described by strike (the direction of a level line on the layer) and dip (the angle and direction of tilt). Faults are cracks where rock has moved. A cross-section shows the rocks as if you cut the ground like a cake, and a stratigraphic column lists the layers in order of age.
Geological Structures: Folds, Faults and Joints – Rock layers (strata) start flat. Forces in the crust squeeze, pull or slide them. Squeezing can bend layers into folds: an arch is an anticline and a trough is a syncline. Strong forces can break rock into faults: in a normal fault the hanging wall moves down (pulling), in a reverse fault it moves up (squeezing), and in a strike-slip fault blocks slide sideways. Folds and faults in a region often line up in the same direction, called the structural trend.

4. Ocean motion and circulation

Hydrostatic pressure · Geostrophic currents · Ocean waves · Storm surges and tsunamis · Tides

Water (Oceans): Hydrological Cycle, Ocean Floor, Temperature and Salinity – The Earth's water keeps moving between oceans, air, land and living things in the hydrological (water) cycle; about 97% of it is in the oceans. The ocean floor has major divisions — continental shelf, continental slope, deep sea plain and ocean deeps (trenches) — and minor features like mid-ocean ridges, seamounts, guyots, submarine canyons, atolls and banks. Ocean surface water is warmest near the equator and colder towards the poles; with depth it falls sharply through a layer called the thermocline, below which the water is near 0–4 °C. Salinity is the salt in sea water, about 35 grams per 1,000 grams (35‰). It rises with evaporation and falls with rain, rivers and melting ice, so it is high in the subtropics and enclosed hot seas and low near the equator, poles and river mouths.
Oceans: The Sea Floor, Moving Water and Life – Oceans cover about 71% of the Earth. Their floor has a shallow continental shelf, a steep slope, a deep plain, underwater ridges and very deep trenches. Water moves in three ways: waves (made by wind), tides (made by the Moon's pull) and currents (rivers in the sea, warm and cold). Oceans give fish, salt, oil, gas and trade routes, and millions of people earn their living from them. Cyclones and tsunamis are ocean hazards; early warning saves lives. International rules (UNCLOS) set how far a country's sea rights reach: 12 nautical miles of territorial sea and a 200-mile Exclusive Economic Zone.
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.
Movements of Ocean Water: Waves, Tides and Currents – Ocean water moves in three ways. Waves are made mostly by wind: the energy moves forward while each bit of water goes round in a small circle; waves slow down and break in shallow water. Tides are the regular rise and fall of the sea, usually twice a day, caused by the Moon's (and Sun's) pull and the Earth–Moon spin. When Sun, Moon and Earth line up (new and full moon) we get very high spring tides; when they are at right angles (quarter moons) we get weak neap tides. Ocean currents are huge rivers of water flowing in fixed directions, pushed by winds, heating, gravity, salinity and density differences, and turned by the Coriolis force. Warm currents flow from the equator towards the poles; cold currents flow from the poles towards the equator. Currents change coastal climates, fishing, fog and shipping.
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.

5. Atmospheric motion

Adiabatic processes · Stability · Hydrostatic balance · Geostrophic and gradient winds · Westerly waves · Scales of motion

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.

6. Planetary motion

Horizon coordinates · Apparent motion of planets · Geocentric vs heliocentric · Synodic period · Kepler's laws

Celestial Coordinates: Finding Any Star in the Sky – Astronomers imagine the sky as a huge celestial sphere around the observer. In the horizon system a star is fixed by its altitude (angle above the horizon) and azimuth (angle from north towards east); both change as Earth turns. In the equatorial system a star is fixed by declination (angle from the celestial equator, like latitude) and right ascension (hours east of the March equinox point, like longitude); these stay almost constant, so star maps use them. The altitude of the celestial pole equals the observer's latitude. Brightness is given by magnitude: smaller numbers mean brighter stars.
The Solar System – The Solar System is the Sun and everything its gravity holds: 8 planets, their moons, dwarf planets, asteroids, comets and dust. The inner four planets (Mercury, Venus, Earth, Mars) are small and rocky. After the asteroid belt come the giants: gas giants Jupiter and Saturn, ice giants Uranus and Neptune. Gravity pulls planets towards the Sun while they move sideways, so they travel in orbits; closer planets move faster and have shorter years. It all formed about 4.6 billion years ago from a spinning cloud of gas and dust.
History of Science: How Our Ideas About Nature Changed – Science grew slowly over 5,000 years. Early civilisations watched the sky to make calendars. Greek thinkers asked why things happen and used reason. Indian and Islamic scholars gave us zero, algebra and careful experiments. In the Scientific Revolution, Copernicus, Galileo and Newton replaced the Earth-centred model with a Sun-centred one and tested ideas by experiment. Modern science brought atoms, evolution, relativity and quantum theory. Each step shows the same lesson: good evidence can overturn old ideas.
Kepler's Laws of Planetary Motion – Kepler gave three rules for how planets move. 1) Each planet moves on an ellipse with the Sun at one focus. 2) The line from the Sun to the planet sweeps equal areas in equal times, so the planet moves faster when it is near the Sun. 3) The square of the time for one round (T²) is proportional to the cube of the semi-major axis (a³). The second law is really conservation of angular momentum. The third law follows from Newton's law of gravitation.

7. Our galaxy and cosmic structure

Cluster colour-magnitude diagrams · Clusters and nebulae · Interstellar extinction · 21 cm hydrogen line · Rotation curve · Galaxy groups and clusters · Large-scale structure

Star Clusters: Open, Globular and How We Find Their Age – A star cluster is a group of stars born together from one gas cloud, so they share the same age and almost the same chemical make-up. Open clusters are loose, young and blue; globular clusters are dense, old and reddish. Plot each star's brightness against its colour and you get a main-sequence curve; the point where it bends away (the turn-off) tells the cluster's age: lower turn-off means older cluster.
The Interstellar Medium: Gas, Dust and Molecules Between the Stars – The interstellar medium (ISM) is the thin gas and dust that fills the space between stars. About 99% of it is gas (mostly hydrogen and helium) and about 1% is tiny solid dust grains. In cold, dense clouds atoms join into molecules such as H₂ and CO. Dust absorbs and scatters starlight, blue light more than red, so a star behind dust looks fainter (extinction) and redder (reddening).
The Milky Way: Our Home Galaxy – The Milky Way is a barred spiral galaxy of about 100–400 billion stars, roughly 100,000 light-years across. It has a thin disc with spiral arms, a central bulge and bar, and a large faint halo with old globular clusters. The Sun sits about 26,000 light-years from the centre in the Orion Arm and orbits at about 230 km/s, once every 230 million years or so. Dust hides much of the disc, so astronomers map the arms using 21 cm radio waves from hydrogen. At the centre is a black hole, Sgr A*, of about 4 million solar masses. The flat rotation curve shows the galaxy holds much more mass than we can see: dark matter.
Dark Matter: The Invisible Mass Holding Galaxies Together – Stars far from a galaxy's centre orbit about as fast as stars near it. If only the visible matter pulled on them, far stars should move slowly. This flat rotation curve means there is extra, invisible mass: dark matter. It does not shine or block light, but its gravity is real. Today's best picture of the cosmos is about 5% ordinary matter, 27% dark matter and 68% dark energy, which makes the expansion speed up.
Cosmology: The Expanding Universe and the Big Bang – Cosmology is the study of the whole universe: its structure, history and future. Galaxies gather in groups, clusters and filaments around huge voids. Distant galaxies are moving away from us, faster the farther they are (Hubble's law, v = H₀d), because space itself is expanding. Running the expansion backwards leads to a hot, dense beginning about 13.8 billion years ago, the Big Bang. The main evidence is redshift, the cosmic microwave background and the amounts of hydrogen and helium. Most of the universe is dark matter and dark energy.