By approximately ________ years ago, ________ had produced oxygen in enough amounts for it to make up a significant fraction of Earth's atmosphere.
A) 100 million; trees and plants
B) 1 billion; trees and plants
C) 250 million; bacteria and algae
D) 2.5 billion; bacteria and algae
E) 2,000; animals and humans

Question

Quizplus · Accepted Answer

The Answer of By approximately ________ years ago, ________ had produced oxygen in enough amounts for it to make up a significant fraction of Earth's atmosphere.
A) 100 million; trees and plants
B) 1 billion; trees and plants
C) 250 million; bacteria and algae
D) 2.5 billion; bacteria and algae
E) 2,000; animals and humans

By Approximately ________ Years Ago, ________ Had Produced Oxygen in Enough

By Approximately Years Ago, Had Produced Oxygen in Enough