atmosphere imp.

• What did green plants evolve to produce?

  Oxygen
• What happened to early CO2 in the oceans?

  A lot of it dissolved
• How was nitrogen gas introduced into the atmosphere?

  Through ammonia reacting with oxygen and denitrifying bacteria
• Why did nitrogen gas increase in the atmosphere?

  It was produced but not broken down
• What did green plants evolve over most of the Earth to produce?

  Oxygen
• What was the effect of plants on CO2 levels?

  They helped lock CO2 into fossil fuels
• What gases did volcanoes release?

  Steam and CO2
• What was the state of the Earth's surface originally?

  It was originally molten
• What formed the thin crust of the Earth?

  The cooling of the molten surface
• What was the composition of the early atmosphere?

  Mostly CO2 and water vapor
• What happened to the water vapor in the early atmosphere?

  It condensed to form oceans
• How did the ozone layer benefit complex animals?

  It blocked harmful rays from the sun
• What was the impact of oxygen buildup on early organisms?

  It killed off organisms that couldn't tolerate it
• What is the current composition of the atmosphere?

  Mostly nitrogen and oxygen
• What percentage of the atmosphere is nitrogen?

  Roughly 78%
• What percentage of the atmosphere is oxygen?

  Roughly 21%
• How can you test for oxygen?

  It relights a glowing splint