Eduqas GCSE Geology Planetary geology: comparing Earth with its neighbours, meteorites, and reading the Moon and Mars

What this module actually demands

Planetary geology takes the processes you learned on Earth, impact, volcanism, weathering, the layered interior, and asks you to apply them across the Solar System. It is a compact module built on one big idea: uniformitarianism, the present is the key to the past, lets us interpret other worlds by comparison with our own. Eduqas tests four linked things here: comparing the Earth with its neighbours, using meteorites as evidence for the Earth's deep interior, applying uniformitarianism to space imagery, and reading the Moon and Mars including the crater-density dating method. The skill is interpretation and comparison rather than recall, so questions reward explaining what a feature shows and why. This overview ties the four dot-point pages together; each has its own page with worked exam questions.

Comparing Earth with its neighbours

The rocky neighbours (the Moon, Mars, Venus, Mercury) are made of similar silicate rocks but differ in surface materials, landforms, atmosphere, temperature, pressure and gravity. Gravity depends on mass: a large body holds an atmosphere, a small one like the Moon cannot. The Earth is active because it is large and still hot inside, and habitable because its distance from the Sun gives liquid-water temperatures and its atmosphere supplies pressure and warmth. A surface densely covered in impact craters signals an old, airless, dead body (no atmosphere to burn up meteorites, no weathering or erosion, no resurfacing), which is why the Earth's own craters are mostly erased while the Moon's survive.

Meteorites as evidence for the Earth's interior

Because we cannot sample the deep Earth, meteorites stand in as samples of a differentiated rocky body. Early bodies separated into a dense iron-nickel core and a silicate mantle; smashed apart, their fragments fall as meteorites. Iron meteorites sample the cores and support an iron-rich Earth core; stony meteorites sample the mantles and support a silicate Earth mantle; stony-iron meteorites sample the boundary. With the Earth's density and earthquake-wave evidence, they confirm the layered, iron-core, silicate-mantle structure, and dating meteorites gives the age of the Earth.

Uniformitarianism and space imagery

Uniformitarianism, the same processes everywhere and at all times, lets geologists read planetary surfaces from space imagery by comparison with Earth landforms: craters record impacts, cones with summit craters record volcanism, branching channels record flowing water (or lava), and dunes record wind. The mix of landforms reveals a body's history and activity. The limits matter for the higher marks: we usually cannot visit to confirm, conditions differ between planets so processes may behave differently, and similar shapes can have different causes.

Reading the Moon and Mars

The Moon has heavily cratered highlands (old, impact-shaped) and smoother dark maria (younger basalt plains that flooded basins as lava), recording impact and volcanism on a dead body. Mars shows giant volcanoes, a vast canyon system, dried-up channels and polar ice and dunes, recording past volcanism and flowing water on a world now cold and dry. Crater density dates surfaces relatively: more craters means older, fewer means resurfaced and younger. This is the planetary version of superposition; ages in years need radiometric dating of samples.

The exam patterns Eduqas repeats

• Compare two bodies. "Compare the Earth and the Moon" rewards a feature-by-feature contrast (atmosphere, activity, craters) explained by size, gravity and atmosphere.
• Reason from a meteorite. Match the type (iron, stony) to the layer it samples (core, mantle) and to the Earth, stressing that we cannot sample the deep Earth directly.
• Interpret a landform image. Use uniformitarianism to name the process (impact, volcanism, water, wind) and add a limitation.
• Order surfaces by crater density. More craters means older; state that this is relative, not absolute, dating.
• Describe the surface of Mars. List features and pair each with the process and history it records.

How to revise this module

1. Make a planet-comparison table. Rows for the Earth, Moon and Mars; columns for atmosphere, temperature, gravity, activity and craters; then learn the cause of each difference.
2. Learn the three meteorite types and the layer each samples, and rehearse the "we cannot sample the deep Earth" argument.
3. Drill landform interpretation. For craters, volcanoes, channels and dunes, state the process and a limitation, applying uniformitarianism each time.
4. Memorise the Moon and Mars features (highlands and maria; volcanoes, canyon, channels, ice) and what each records.
5. Practise crater-density ranking and be ready to say why it is relative dating only.

Use the four dot-point pages for the detail and worked exam questions; this guide is the map that connects them.