What's the most common gas in today's atmosphere?

• Oxygen

• Nitrogen

• Carbon dioxide

What percentage of our current atmosphere is nitrogen?

• 100%

• 78%

• 28%

In the early atmosphere what was the most common gas?

• Oxygen

• Carbon dioxide

• Nitrogen

Why did oxygen levels begin to increase in the atmosphere?

• Photosynthesis produces oxygen

• The water condensed

• There were volcanoes

Why did carbon dioxide levels in the atmosphere decrease?

• Volcanoes released CO2

• The oceans absorbed CO2

• Animals evolved to do respiration

What gas is taken in for photosynthesis?

• Oxygen

• Carbon dioxide

• Nitrogen

The average temperature on Earth has done what over the past 4 billion years?

• decreased

• increased

• stayed the same

Now when we burn fossil fuels they release CO2 which causes...

• volcanoes to erupt

• earthquakes

• global warming