Posted: August 12th, 2016

Oxygen built up in the atmosphere approximately 2 billion years ago and

Oxygen built up in the atmosphere approximately 2 billion years ago and

A. could not have occurred without the oxygen coming from outer space.

B. occurred due to carbon dioxide being split by lightning strikes.

C. occurred because aerobic organisms required the oxygen.

D. destroyed ozone forming more oxygen.

E. helped to form the ozone layer that is so important to life today.