Final Exam: Earth's Formation

An Impact Crater is ______.

• Removal of surface material through weathering by agents such as wind and water
• Process that occurs when a nucleus decays and emits alpha, beta or gamma radiation
• A crater on a planet or moon caused by the impact of a meteorite or other object, typically circular with a raised rim.
• Atoms of the same element that differ in the number of neutrons

True or False. Earth’s surface does not illustrate many impact craters whereas Moon’s surface illustrates many impact craters.

• True
• False

The Earth, unlike the Moon, has few obvious impact craters because _____________.

• Few asteroids have struck the Earth
• Earth's atmosphere absorbs the kinetic energy of asteroids
• Most impacts occur in Antarctica where they are yet to be discovered
• Earth is an active and dynamic planet whose surface is constantly undergoing change

The most common type of meteorites discovered on Earth is _____________________.

• Chondrites
• Iron meteorites
• Tektites
  
• Stony meteorites

Earth is protected from most meteorite impacts by ___________________.

• U.S. Strategic Meteorite Interception Program (SMIP)
• Its gravitational field
  
• Its atmosphere
  
• Solar Wind

Evidence that the depression called Meteor Crater in Arizona was the result of a meteorite impact includes ____________________.

• A steep-sided and closed crater
• Inverted piles of sedimentary rocks
  
• Surrounding sedimentary layers dipping away from the crater
• All are correct

Relatively few impact craters have been discovered on Earth because ________________.

• Over 70% of the Earth is covered by oceans.
• Weathering and erosion erase them.
  
• All are correct
• Some of the crust gets recycled by subduction.

When did the Earth form? 

• 10 billion years ago 
• 4.6 billion years ago 
• 446 million years ago 
• 6,000 years ago