The Great Oxygenation Event Was a Time in the Middle

question 17

Multiple Choice

The Great Oxygenation Event was a time in the middle Proterozoic when

• A) organisms that produce oxygen first originated.
• B) oxygen began to accumulate as a gas in the atmosphere.
• C) the oxygen concentration in the atmosphere reached its present concentration of
• 21 percent.
• D) excessively high concentrations of oxygen in the atmosphere caused a mass extinction.