Earth Science: Earth and space, weather and climate, rocks, celestial bodies
What the Earth science section asks
This domain tests Earth and space, weather and climate, rocks and geology, and celestial bodies. Questions use cross-sections, weather maps, rock-cycle diagrams and simple astronomical data; you must interpret evidence and distinguish long-term climate from short-term weather.
Core rules
- Earth and space: Earth rotates on its axis once about every 24 hours, causing day and night; it orbits the Sun in about 365.25 days, causing the seasons because the axis is tilted. The Moon orbits Earth and shows phases as its illuminated half is seen from different angles.
- Weather and climate: Weather is the short-term state of the atmosphere; climate is the long-term average. Air pressure, temperature, humidity and wind describe weather. Warm air rises and cools, forming clouds; cold fronts bring rapid cooling and rain.
- Rocks and geology: Igneous rock forms from cooled magma or lava; sedimentary rock forms from compacted sediments; metamorphic rock forms when heat and pressure alter existing rock. Fossils are most common in sedimentary rock.
- Celestial bodies: The Solar System has eight planets, with terrestrial planets near the Sun and gas/ice giants farther out. Stars produce energy by nuclear fusion; galaxies contain vast numbers of stars.
Worked example
An earthquake sends P-waves at 6.0 km/s and S-waves at 4.0 km/s. A station records the S-wave 10 s after the P-wave. How far away is the epicentre? Let distance be d km. P-wave time = d/6.0; S-wave time = d/4.0. The difference is 10 s: d/4.0 − d/6.0 = 10. Multiply by 12: 3d − 2d = 120, so d = 120 km. The reasoning uses the slower S-wave arriving later; the lag grows with distance.
Traps
Confusing weather with climate; thinking seasons are caused by Earth's changing distance from the Sun rather than axial tilt; labelling any rock with layers as metamorphic; forgetting that S-waves cannot travel through liquids; and reversing the order of planets or Moon phases.