AstronomyLesson 2 of 3 in the course Other Worlds: An Introduction to the Solar System

Dating Planetary Surfaces with Craters and Radioactive Isotopes

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Planetary surfaces preserve clues about their histories, but geological activity can erase those clues. In this lesson, we explore how astronomers use impact craters to compare the ages of different regions on solid worlds—and what crater counts can and cannot tell us.

Impacts have occurred across the solar system for billions of years. Over long periods, the impact rate has been roughly constant. If a surface remains unchanged, it accumulates craters over time. Therefore, a region with more craters has generally been exposed for longer than a region with fewer craters.

All flashcards

What does crater counting estimate most directly?
How long a surface has been exposed since it was last substantially changed, based on its preserved impact craters.
How can parent and daughter isotopes help date a rock?
Their measured amounts, together with the decay system’s half-life, can indicate how long radioactive decay has occurred.
What is a half-life?
The time in which half the radioactive parent nuclei in a large sample are expected to decay.
Why can radioactive decay contribute to a planet’s internal heat?
Decay releases energy, and the combined energy from many nuclei can be substantial.
What did dating Apollo lunar samples make possible?
Establishing a numerical geological chronology for the Moon.

Quiz questions

  1. A sample begins with a large population of radioactive parent nuclei. About what fraction remains after three half-lives?Answer: One-eighth of the original population
  2. How does comparing parent and daughter isotopes help scientists date a rock?Answer: It indicates how long decay has occurred in the rock, given the decay system’s half-life.
  3. What did analysis of the first Apollo lunar samples in 1969 help establish?Answer: A numerical geological chronology for the Moon
  4. About what fraction of Earth’s present internal heat budget is estimated to come from radioactive decay?Answer: About one-half
  5. Which statement distinguishes crater counting from radioactive dating?Answer: Crater counts usually compare surface ages, while isotope measurements can provide numerical rock ages.

Based on Astronomy 2e by Andrew Fraknoi, David Morrison, Sidney Wolff (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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