CH. 1.2 - Earth's Craters vs. Moon's Crater Preservation

Oct 2, 2024

Lecture Notes: Why Earth Has Fewer Impact Craters Than the Moon

Introduction

  • Earth exhibits fewer impact craters compared to the Moon.
  • The Earth is dynamic with geological activities that erase evidence of impact craters over time.

Examples of Meteorite Impact Craters on Earth

Meteorite Crater, Arizona

  • Size: Created by an object the size of an 18-wheel tractor trailer.
  • Characteristics: Ridge around the edge is from debris thrown out during impact.
  • Age: Less than 50,000 years old.

Namibia Crater, Southwest Africa

  • Size: Double the size of the Arizona crater.
  • Characteristics: Much shallower due to 4 million years of erosion.

Chicxulub Crater, Mexico

  • Significance: Impact that led to dinosaur extinction 65 million years ago.
  • Size: Gigantic, 156 miles in diameter.
  • Description: Crater is a mile underground, discovered through seismic imaging.
  • Impact Consequences: Fireball incinerated half the planet, debris blocked sunlight leading to mass extinction.
    • Resulted in a global layer rich in iridium and other impact evidence.
  • Discovery: Found by oil companies surveying for oil, found shattered rocks and glass.

Manicouagan Crater, Quebec, Canada

  • Observation: Seen from space, distinctive ring-shaped lake.
  • Characteristics: Size is about 60 miles across, over 200 million years old.
  • Formation: Impact at a higher altitude, later shaped by glacial erosion.
  • Glacial Action: Softer rock eroded by glaciers, forming a lake.

Geological Processes on Earth

  • Erosion and Deposition: Over time, craters are filled in, buried, and eroded away.
  • Plate Tectonics: Earth's surface is recycled; old plates subduct, and their features are lost.

Contrast with the Moon

  • The Moon lacks geological processes; its surface remains unchanged for billions of years.
  • Craters on the Moon are preserved due to lack of dynamic geological activity.

Conclusion

  • Earth's dynamic processes (erosion, deposition, tectonics) contribute to the removal of impact craters over time, unlike the Moon which remains geologically inactive.