Earth Science - 地層と岩石・地震と火山・気象と天体
地層と岩石
Sedimentary rocks form in layers; coarser grains settle near the shore, finer mud farther out, and limestone indicates shells. Igneous rocks are volcanic (quick cooling, fine crystals) or plutonic (slow cooling, coarse crystals); metamorphic rocks form under heat and pressure. Unless the strata are disturbed, lower layers are older, and index fossils date them. Unconformities, folds and faults record later movement, while weathering, erosion, transport and deposition shape the surface.
地震と火山
P waves arrive first and pass through solids and liquids; S waves are slower and cannot pass through liquid, which reveals the outer core. The S–P time difference grows with distance from the epicentre. Magnitude measures energy released; intensity (震度) measures shaking at a place - never confuse them. Volcanoes reflect magma viscosity: silica-poor basalt flows quietly, silica-rich magma erupts explosively.
気象と天体
Humidity, dew point, condensation and cloud formation explain rain; high and low pressure, air masses and fronts let you read a weather map. Earth's rotation gives day and night, and its tilted revolution gives seasons - not distance from the Sun. Moon phases repeat about every 29.5 days; a solar eclipse needs a new moon, a lunar eclipse a full moon.
Rule of thumb. Distance to an epicentre ≈ 8 km × (S-wave arrival time − P-wave arrival time, in seconds). Always check the units.