Earth and Space Science
Earth and Space Science covers Earth's interior and plate tectonics, the rock cycle, surface processes, the atmosphere and hydrosphere, geologic time, and the solar system, stars, and Earth–Moon–Sun relationships. Items often ask you to order events, interpret a cross-section, or explain an astronomical cycle.
Solid Earth
- Layers: crust, mantle, liquid outer core, solid inner core. P-waves travel through solids and liquids; S-waves cannot pass through liquids.
- Plate boundaries: divergent (seafloor spreading, ridges), convergent (subduction, mountains), transform (faults, earthquakes).
- Rock cycle: igneous (cooled magma), sedimentary (compaction and cementation), metamorphic (heat and pressure).
- Relative dating uses superposition, cross-cutting relationships, and index fossils; absolute dating uses radiometric half-lives.
Earth in space
- Seasons result from the 23.5° axial tilt changing sunlight angle and day length - not from distance to the Sun.
- Moon phases reflect orbital geometry; spring tides occur at new and full moons, neap tides at quarters.
- The solar system has rocky inner planets and gas/ice giants farther out; gravity governs orbits.
Atmosphere and water
- Uneven solar heating drives convection, winds, and the Coriolis deflection of moving air.
- Weather is short-term atmospheric state; climate is long-term averages and patterns.
Worked example
A mineral grain contains 12.5% of its original radioactive parent isotope. Each half-life halves the parent: 100% → 50% → 25% → 12.5%, which is three half-lives. If the half-life is 700 million years, the mineral is 3 × 700 million = 2.1 billion years old. The reasoning works because the parent fraction depends only on how many half-lives have elapsed.
Traps that cost marks
- Explaining seasons by Earth's distance from the Sun.
- Saying S-waves pass through the outer core.
- Treating a feature that cuts across layers as older than those layers.
- Confusing weathering (breakdown in place) with erosion (transport).