Summary:
- The early Earth had no atmosphere or free water.
- The planet was far too hot for gases and water to collect.
- The gases came from volcanic eruptions and from comets.
- Nitrogen, carbon dioxide, hydrogen, and water vapor, or water in gas form, were in the first atmosphere.
- There was very little oxygen in the atmosphere until plants evolved.
- Plants produce oxygen as a product of photosynthesis.
- Oxygen allowed animals to evolve and ozone to form.
- Ozone in the upper atmosphere blocks harmful solar radiation from reaching the surface.
Hmm...
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