South 고등학교 3학년 Earth Science I
Chapters: 6
1. Changes in the geosphere
From drift to plate tectonics · Continents through time · Mantle convection and plumes · Magma at plate boundaries
- 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.
- Igneous Rocks: From Hot Magma to Solid Stone – Igneous rocks form when melted rock cools and turns solid. Melted rock underground is magma; on the surface it is lava. Magma forms where rock gets hot enough, or where pressure drops or water is added, mostly at plate boundaries and hot spots. Magma is lighter than solid rock, so it rises. If it cools slowly deep underground, crystals grow big (intrusive rocks such as granite and gabbro). If it cools fast at the surface, crystals stay tiny or glass forms (extrusive rocks such as basalt, rhyolite, obsidian and pumice). Silica content decides colour and stickiness: low-silica (mafic) magma is dark, hot and runny and erupts gently; high-silica (felsic) magma is light, cooler and sticky, traps gas and erupts explosively.
2. Earth's history
Sedimentary structures · Geological structures · Relative dating · Absolute dating · Geological periods
- Sedimentary Rocks: Layer by Layer into Stone – Sedimentary rocks form at Earth's surface from bits of older rock, minerals that come out of water, or remains of living things. Weathering breaks rock into sediment; erosion and transport by rivers, wind, ice and waves carry it; when the flow slows, sediment is deposited in layers (strata), usually in seas, lakes, rivers and deserts. The oldest layer is at the bottom (law of superposition). Diagenesis turns loose sediment into rock: compaction (the weight of layers above squeezes grains and pushes water out) and cementation (minerals such as calcite, silica and iron oxide crystallise between grains and glue them). Clastic rocks are named by grain size: conglomerate and breccia (gravel), sandstone (sand), siltstone, and shale or mudstone (clay). Chemical rocks form from minerals that precipitate from water: rock salt, gypsum, some limestone, chert. Organic (biogenic) rocks form from remains of living things: coal, chalk and shelly limestone. Sedimentary rocks cover about 75% of the land surface, hold almost all fossils, oil, gas, coal and groundwater, and their structures (bedding, cross-bedding, ripple marks, mud cracks, graded bedding) tell us about past environments.
- 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.
- Radiometric Dating – Relative dating puts rocks and fossils in order (lower layers are usually older). Absolute (radiometric) dating gives an age in years. A rock crystal traps radioactive parent atoms that decay at a fixed rate into daughter atoms. After each half-life, half of the parent atoms are left. Measuring the daughter-to-parent ratio gives the age: t = T½ × log₂(1 + D/P).
3. Atmosphere and ocean change
Passing weather systems · Typhoons · Severe weather · Seawater properties
- 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.
- Extreme Weather – Extreme weather is weather far from the usual: heatwaves, cold waves, heavy rain and floods, droughts, cyclones, thunderstorms, hail, heavy snow and dust storms. A warmer world slides the whole pile of weather, so very hot days and heavy rains become more common.
- 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.
4. Atmosphere-ocean interaction
General circulation and surface currents · Deep ocean circulation · El Niño and upwelling · Causes of climate change
- 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.
- Earth's Geography and Climate: Rain Shadows, El Niño and La Niña – Climate depends on geography. Latitude sets how much sunlight arrives; air rising at the equator and sinking near 30° makes rainforests and deserts (the Hadley cell). Altitude cools air about 6.5 °C per km. Oceans warm and cool slowly, so coasts have milder climates, and ocean currents carry heat. Mountains force moist wind upward, giving rain on the windward side and a dry rain shadow behind. El Niño is when Pacific trade winds weaken and warm water spreads east, shifting rain and changing weather worldwide; La Niña is the opposite, with stronger trade winds and a colder east Pacific.
- Climate Change and the Greenhouse Effect – Climate is the average weather of a place over about 30 years. Greenhouse gases like carbon dioxide and methane trap some of the heat the Earth gives off. Humans have added a lot more of these gases by burning fossil fuels and cutting forests, so the Earth is warming. This causes melting ice, rising seas and more extreme weather. We can cut emissions (mitigation) and prepare for changes (adaptation).
5. Stars and exoplanet systems
Temperature and size from spectra · The H-R diagram · Evolution of Sun-like stars · Energy in main-sequence stars · Exoplanet detection · Life elsewhere
- Stars: Colour, Brightness, Distance and the H-R Diagram – A star is a huge ball of hot gas that shines by nuclear fusion. Its colour shows its surface temperature: red stars are cool, blue stars are hot (Wien's law: λmax × T = 2.9 × 10⁻³ m K). Stars are sorted into spectral classes O B A F G K M, hottest to coolest. How bright a star looks (apparent magnitude) depends on its real power (luminosity) and its distance, because light weakens as 1/d². Nearby distances are found by parallax: d (pc) = 1/p (arcsec). Luminosity depends on size and temperature (L = 4πR²σT⁴). The H-R diagram plots luminosity against temperature and shows the main sequence, giants and white dwarfs.
- Nuclear Fusion – In nuclear fusion, light nuclei join to make a heavier nucleus and release energy. In the Sun's core, at about 15 million °C, four hydrogen nuclei join in steps (the proton–proton chain) to make one helium nucleus. The helium weighs about 0.7% less than the four hydrogens; that missing mass becomes energy by E = mc². Gravity squeezing in and fusion heat pushing out keep a star steady for billions of years.
- Exoplanets: How Do We Find Planets Around Other Stars? – An exoplanet is a planet that goes round a star other than the Sun. Planets are tiny and dim next to a star, so we mostly find them by clues. In the transit method, a planet crosses in front of its star and the star's light dips by about (planet size / star size) squared. In the radial velocity (wobble) method, the planet's pull makes the star move in a tiny circle, and its light shifts blue and red. The time between dips or wobbles gives the planet's year. Other methods are direct imaging and microlensing. More than 5,000 exoplanets are known.
- Astrobiology: Is There Life Beyond Earth? – Astrobiology is the science that asks whether life exists beyond Earth. Life as we know it needs liquid water, energy and carbon chemistry. The habitable (Goldilocks) zone is the range of distances from a star where a planet could keep liquid water. Scientists search Mars, icy moons such as Europa and Enceladus, and thousands of exoplanets, look for biosignatures in their air, and listen for signals (SETI). The Drake equation estimates how many talking civilisations might exist; the Fermi paradox asks why we have not heard from any.
6. Galaxies and cosmic expansion
Galaxy types · Big Bang evidence · Dark matter and dark energy
- Stars and Galaxies: From Starlight to the Big Bang – Everything we know about stars comes from their light. Splitting starlight into a spectrum shows dark lines that tell us which elements a star has; the colour tells us its temperature (blue = hot, red = cool) and stars are sorted into classes O B A F G K M. The H-R diagram plots true brightness against temperature: most stars, including the Sun, lie on the main sequence, with giants top right and white dwarfs bottom left. A star is born in a nebula and its mass decides its life: a Sun-like star becomes a red giant and then a white dwarf; a star of more than about 8 solar masses becomes a supergiant, explodes as a supernova and leaves a neutron star or black hole. Stars gather in galaxies, which are spiral, elliptical or irregular. Distances are huge, so we use the astronomical unit, the light-year and the parsec. Galaxies are moving apart, faster when farther (Hubble's law), which together with the cosmic microwave background supports the Big Bang about 13.8 billion years ago.
- 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.
- 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.