| A | B |
|---|
 | As earth cooled, gases from these filled the atmosphere |
| This was responsible for oxygen filling the ocean and early atmosphere |  |
| One of the ways in which water was brought to earth |  |
 | About 4.6 billion years ago, this formed from the accretion of leftover material from the Solar System |
| First Atmosphere | Made of hydrogen and helium that drifted off into space |
| Second Atmosphere |  |
| Oceans | Developed after earth cooled enough for water vapor to condense and precipitate down on the planet |
| Age of earth | 4.6 billion years |
| Sources of water vapor | Volcanoes, Comets and Asteroids |
| The reason the first atmosphere disappeared | It was too hot for gases to remain in the atmosphere |
| Third Atmosphere | Photosynthesis by cyanobacteria changed the planet |
