The Great Oxygen Event Marks the Time, Approximately 2

Multiple Choice

The Great Oxygen Event marks the time, approximately 2.5 billion years ago, when ______ .

A) there was enough oxygen in the atmosphere to support a major burst of life on Earth
B) there was a massive volcanic eruption that lead to a very rapid increase in oxygen levels on Earth
C) there was significant oxygen in the atmosphere
D) there was a cataclysmic weather event that absorbed most of the oxygen in the atmosphere and locked it into iron deposits in the oceans
E) photosynthesis was clearly established and producing oxygen