Astronomy › Section G · The solar system and Earth › Topic G.3
Dating planetary surfaces
How can anyone know that a patch of the Moon is older than a patch of Mars, or that a rock is 3.8 billion years old? Two clocks do the job: craters that pile up over time, and radioactive atoms that decay at a fixed rate.
In this topic
- Surface age is not planet age
- Counting craters
- A clean slate, not a clock that never stops
- Worked example: two regions of one moon
- Radioactive decay
- Turning decay into an age
- The clocks geologists use
- Worked example: a uranium–lead age
- What the dates have revealed
- Radioactivity as a heat source
- Common mistakes to avoid
- Key takeaways
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