Was There Always Oxygen on Earth?

Describe how organisms on Earth contributed to the big change in how much oxygen there was in Earth's early atmosphere.

Oxygen on Earth

Oxygen on Earth

When the Earth was first formed, about 4.6 billion years ago, there was almost no oxygen in the atmosphere. Because the early Earth was very hot, there were a lot of volcanoes. Two of the things that come out of volcanoes are water (which formed the oceans) and carbon dioxide (CO2). The first organisms that developed on Earth used that carbon dioxide and produced oxygen. Over the course of billions of years, enough oxygen was in the atmosphere to do two major things. The first was that the oxygen could be changed into ozone, in order to help protect the Earth from ultraviolet rays (UV). UV rays can kill cells, so it was very important that there was a layer of ozone before plants, animals and fungi (all multicellular organisms) could develop.

The second major consequence of oxygen in the atmosphere was that animals and some fungi could then use that oxygen to breathe. Even more importantly, those animals and fungi give off carbon dioxide so that the amount of oxygen and carbon dioxide stays about the same.

Right now, global warming is happening because there is too much carbon dioxide in the atmosphere. This is because we are burning things (and burning requires oxygen) that have carbon in them, like gasoline. Just like the volcanoes, carbon dioxide is given off into the atmosphere when you burn anything with carbon.

1. What protects the Earth from UV rays?
2. Name two chemicals that are released by volcanoes.
3. What do animals breathe in? What do animals breathe out?
Put it together
4. Explain why the amount of oxygen in the atmosphere increased soon after the Earth was formed.
5. What did volcanoes do for the Earth's early atmosphere?
Think about it
6. Create a cycle (you can use the graphical organizers to help you) showing what happens to oxygen and carbon dioxide on Earth. Include plants, animals, the ozone layer and the ocean in your cycle.
7. Name a famous theory about anything that you are familiar with.

9. Describe the two types of cells.

  1. Where exactly do you find chloroplasts? Be very specific!
  2. What color are the chloroplasts? What gives them that color?
  3. In the diagram, where does the energy come from?
  4. How does solar energy get to animals?
  5. Before eukaryotes, there was an abundance of CO2 in the atmosphere. Of plants or animals, which do you think developed first? Why?
  6. Summarize the exchange of gases in plants and animals.
  7. CO2 traps heat in the atmosphere of Earth. What are two factors that contribute to this excess of CO2?

Major Earth Cycles