It took approximately ________ years for oxygen to become a large component of Earth's atmosphere.
A) 3,000
B) 1 million
C) 3 billion
D) 1 billion

Name: It took approximately ________ years for oxygen to become a large component of Earth's atmosphere. A) 3,000 B) 1 million C) 3 billion D) 1 billion
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It took approximately 1 billion years for oxygen to accumulate in the Earth's atmosphere to significant levels, primarily due to the photosynthetic activity of cyanobacteria.

It Took Approximately ________ Years for Oxygen to Become a Large