GeologyLesson 2 of 2 in the course Earth as a Planet

Earth's Cosmic Impacts: Craters, Extinctions, and Planetary Defense

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

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Summary

Earth has been struck by asteroids and comets throughout its history, just as the Moon has. Yet Earth’s surface does not display nearly as many visible craters. This lesson explains why impact scars are difficult to find on our active planet.

The Moon is close to Earth in cosmic terms, and both bodies have traveled through the same broad population of interplanetary debris. Earth therefore has not escaped the impacts that have marked the lunar surface. Its larger size also gives it a substantial target area.

All flashcards

Meteorite
A fragment of cosmic material that survives passage through the atmosphere and reaches the ground.
Ecological niche
The role and resources available to an organism within an ecosystem.
Evolutionary bottleneck
An event or sequence of events that greatly reduces the diversity of surviving life.
Near-Earth object
An asteroid or comet whose orbit brings it close to Earth.
DART mission
A NASA mission that altered the orbit of asteroid moonlet Dimorphos by spacecraft impact.

Quiz questions

  1. Why did the 1908 Tunguska event produce no impact crater?Answer: The object broke apart in the atmosphere before reaching the ground.
  2. Why does iridium in the end-Cretaceous boundary layer support a cosmic-impact explanation?Answer: Iridium is rare in Earth's crust but relatively abundant in asteroids and comets.
  3. What was one consequence of dust blocking sunlight after the Chicxulub impact?Answer: Reduced sunlight disrupted plants and the food supplies that depended on them.
  4. What two factors does the Torino Impact Hazard Scale combine?Answer: Collision probability and potential damage associated with the object's kinetic energy.
  5. What did NASA's DART mission demonstrate?Answer: A spacecraft collision can slightly alter an asteroid moonlet's orbit.

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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