How long did it take for oxygen to build up in the Earth's atmosphere to its present levels?
A) at least 542 million years
B) at least 360 million years
C) at least 2 billion years
D) at least 3.5 billion years

Question

Quizplus · Accepted Answer

It took at least 2 billion years for oxygen to accumulate in Earth's atmosphere to its present levels. This process, known as the Great Oxidation Event, began around 2.4 billion years ago but took a long time to reach the levels we see today. Oxygen levels gradually increased due to photosynthetic organisms, fundamentally altering Earth's atmosphere and enabling the development of aerobic life forms.

How Long Did It Take for Oxygen to Build Up