• 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.
Select from the frequently asked questions below
Empty List


Looks like no questions have been asked for this concept. Would you like to ask your own question?