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Author Question: How long did it take for oxygen to build up in the Earth's atmosphere to its present levels? A) ... (Read 76 times)

809779

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on: Jul 27, 2018
How long did it take for oxygen to build up in the Earth's atmosphere to its present levels?
 
  A) at least 542 million years
  B) at least 360 million years
  C) at least 2 billion years
  D) at least 3.5 billion years

Question 2

Express the following number to three significant figures: 21.25 m
 
  What will be an ideal response?


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blakeserpa

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Reply #1 on: Jul 27, 2018
Answer to Question 1

C

Answer to Question 2

21.3 m


809779

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Reply 2 on: Jul 27, 2018
Great answer, keep it coming :)

momolu

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Reply 3 on: Yesterday
Wow, this really help

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