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> Today geologists know that the youngest of the hard, crystalline rocks are 1.7 billion years old, whereas the oldest in the sandstone layer were formed 550 mi

by jb1991 5y ago

> Today geologists know that the youngest of the hard, crystalline rocks are 1.7 billion years old, whereas the oldest in the sandstone layer were formed 550 million years ago. Isn’t this backward? Why is the oldest about 1 billion years later than the youngest?

_Microft 5y ago
Maybe it helps if I remove some of the details: youngest of group A is x years old, oldest of group B (which is different from group A) is y years old
- jb1991 5y ago
  Oh thanks, that makes sense. I found that phrase very confusing.