- Photosynthesis is a source of oxygen
- A source of something increases the amount of that something
- Therefore, photosynthesis increases the amount of oxygen in the atmosphere

- Photosynthesis increases the amount of oxygen in the atmosphere
- The photosynthetic life performs photosynthesis
- So, photosynthetic life increases the amount of oxygen in the atmosphere

- Early photosynthetic life is a kind of photosynthetic life
- Early photosynthetic life existed a long time ago
- Hence, early photosynthetic life is a kind of photosynthetic life that existed a long time ago

- Photosynthetic life increases the amount of oxygen in the atmosphere
- Early photosynthetic life is a kind of photosynthetic life that existed a long time ago
- Therefore, early photosynthetic life increased the amount of oxygen in the atmosphere a long time ago

- Early photosynthetic life increased the amount of oxygen in the atmosphere a long time ago
- Earth had no / little oxygen a very long time ago
- Oxygen level describes an amount of oxygen
- Therefore, early photosynthetic life increased the oxygen level in earth 's atmosphere

Hence, early photosynthetic life increased the oxygen level in earth 's atmosphere
Question
Which of the following best describes a change in Earth's atmosphere made by early photosynthetic life?

Context
- Photosynthesis is a source of oxygen 
- Early photosynthetic life is a kind of photosynthetic life 
- Earth had no / little oxygen a very long time ago 
- The photosynthetic life performs photosynthesis 
- Early photosynthetic life existed a long time ago 
- A source of something increases the amount of that something 
- Oxygen level describes an amount of oxygen