History of the Moon's Surface

Clues about the two main kinds of surface

• maria.
  • flat
  • roughly circular, with mountain rims.
  • not many craters
  • rocks are like basalt rocks on Earth (from volcanos)
  • rocks dated at 3.1 to 3.8 billion years.
• highlands.
  • not flat
  • many craters.
  • rocks dated 3.9 to 4.4 billion years

Even if we didn't have dates for lunar rocks based on radioactive decays, how could you tell that the rocks in the maria should be younger than the rocks in the highlands?

This suggests a possible history.

• 4.6 billion years ago, the magma ocean.
  
• 4.4 billion years ago, crust starts to form.
• 4.4 to 4.0 billion years ago, era of the highlands
  • crater formation.
  • lava flows.
  • some craters were giant.
  
• 3.8 to 3.1 billion years ago, maria formation
  • lava flows into the giant craters.
  

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