Earth and Space Science
The Earth and Space Science domain tests Earth's materials and processes, plate tectonics, geologic time, atmosphere and climate, the water cycle, and the solar system and stars. Questions often ask you to infer sequence or scale from evidence.
Core rules and concepts
- Plate tectonics: divergent boundaries create new crust; convergent boundaries produce subduction, mountains, or volcanoes; transform boundaries cause lateral faulting.
- The rock cycle links igneous, sedimentary, and metamorphic rocks through melting, weathering, deposition, compaction, and heat/pressure.
- Relative dating uses superposition (older layers below younger ones, unless overturned) and cross-cutting relationships (a fault or intrusion is younger than the rocks it cuts).
- Absolute dating uses radioactive decay. After one half-life, half the parent remains; after two, one quarter; and so on.
- Seasons result from Earth's axial tilt, not distance from the Sun. Moon phases result from the changing angle between Earth, Moon, and Sun.
- Weather is short-term atmospheric conditions; climate is long-term averages and patterns. The greenhouse effect warms Earth's surface.
Worked example
A rock sample contains 25% of a radioactive parent isotope and 75% of its stable daughter. The isotope's half-life is 10 million years. After one half-life, 50% parent remains; after two half-lives, 25% remains. Because 25% is one-quarter, two half-lives have passed: 2 × 10 million = 20 million years. The daughter fraction confirms the parent loss.
Traps that cost marks
- Explaining seasons by Earth's distance from the Sun.
- Confusing moon phases with eclipses.
- Reading superposition in overturned strata without checking evidence.
- Mixing weather and climate.
- Forgetting that parent isotope decreases by half each half-life, not by a constant amount.