Meteors and Meteorites Notes

Module 7: Meteors and Meteorites

Definition of Key Terms

  • Meteoroid
  • Small rocky or metallic object
  • Located in outer space
  • Generally less than 10m in size

Characteristics of Meteors

  • Meteor
  • A meteoroid that vaporizes upon entering Earth’s atmosphere
  • Often seen as a flash or streak of light in the night sky
  • Compositions
    • Pieces of meteoroids, asteroids, or comets
  • Frequency of visibility
    • Approximately one meteor can be observed every 10 minutes
  • Commonly referred to as “shooting stars”

Understanding Meteorites

  • Meteorite
  • A meteoroid that survives its passage through the atmosphere and lands on Earth
  • Contributes to Earth’s mass, adding approximately 300 tons per day
  • Characteristics
    • Usually very small but dense
    • Most often composed of rock; some are made of iron and nickel
    • Similar in composition to terrestrial rocky planets and the moon

Types of Meteorites

  • Classifications of Meteorites
  • Stony Meteorites
    • Look like ordinary rocks
  • Iron Meteorites
    • Very dense, metallic appearance
  • Stony-Iron Meteorites
    • The rarest type; contains both stony and metallic elements

Carbonaceous Meteorites

  • Characteristics
  • Typically black or dark gray
  • Originates from carbonaceous asteroids
  • Significance
  • Radiometric dating indicates they are very old (4.4-4.6 billion years old)
  • Similar in age to Moon rocks

Impacts on Earth

  • Historic Meteor Events
  • Tunguska Event (1908)
    • Occurred in Siberia, caused by an 80m meteoroid
    • Exploded in the air with energy comparable to a 10 megaton nuclear bomb
    • Resulted in darkened skies in California
  • Chelyabinsk Event (2013)
    • Exploded 20 miles above a lake in Russia
    • Resulted in 1600 injuries but zero fatalities

Craters on Earth

  • Formed by large meteorite impacts
  • Over 200 craters identified on Earth, with less than 500 million years old
  • Barringer Crater
  • Formed by a 200,000 ton meteoroid (50m in diameter)
  • 25 tons of fragments discovered

Meteor Showers

  • Occur when Earth passes through debris trails left by comets
  • Approximately 30 meteor showers occur annually
  • Named after the constellation from which they appear to originate

Notable Meteorites

  • Allende Meteorite
  • Discovered in Mexico in 1969
  • Contained isotopes formed during supernova events, dated to 4.6 billion years ago
  • Suggests that the solar system may have formed from a supernova shockwave

Mass Extinctions Related to Asteroids

  • Cretaceous-Paleogene Extinction (65 million years ago)
  • First hypotheses discovered in Italy
  • Possible causes include dust blocking sunlight or resulting wildfires
  • Chicxulub Impact Crater
    • Evidence found in Mexico, with structure partially on land and partially underwater
  • Evidence of Prior Extinction Events
  • Additional findings indicate another mass extinction occurred 250 million years ago as a result of asteroid impact.