The current oxygen level in the Earth's atmosphere was reached about
A) 4.6 billion years ago.
B) 2 billion years ago.
C) 20 million years ago.
D) 250 million years ago.
E) 540 million years ago.

Question

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The Answer of The current oxygen level in the Earth's atmosphere was reached about
A) 4.6 billion years ago.
B) 2 billion years ago.
C) 20 million years ago.
D) 250 million years ago.
E) 540 million years ago.

The Current Oxygen Level in the Earth's Atmosphere Was Reached