Approximately _________ years ago, _________ began producing oxygen in enough amounts to be a significant fraction in the 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 process of oxygenic photosynthesis, which began in bacteria and algae, started approximately 2.5 billion years ago and gradually increased the amount of oxygen in the Earth's atmosphere. Trees and plants became important oxygen producers much later, about 250 million years ago. Animals and humans, on the other hand, are oxygen consumers and did not contribute significantly to the production of oxygen in the atmosphere.

Approximately _________ Years Ago, _________ Began Producing Oxygen in Enough

Approximately _ Years Ago, _ Began Producing Oxygen in Enough