The slow build up of Oxygen in the Earth's Atmosphere

Click on image for full size version (43K JPG) Image from: Kentucky Coal Education Web Site

The table at the left shows just how slowly it took for oxygen to accumulate in the atmosphere. 3.5 BYA there was only 0.01% oxygen in the atmosphere. 2.5 BYA there was only 0.1% oxygen in the atmosphere. Imagine how hard it would be to breathe in such an environment. At the top of Mt. Everest (where it is very hard to breathe!) there is enough oxygen to be equivalent to 18% levels.

The formation of life on Earth played a very large role in the build up of oxygen in the environment. As early as 3.5 BYA, photosynthetic bacteria began to produce oxygen as a waste product of their activity. That oxygen reacted with iron in the ocean to make iron ore. Later, after the iron in the ocean was gone, and the making of iron ore was finished, about 2.5 BYA, enough oxygen accumulated for respiration (for animals which breathe oxygen) to begin in simple organisms, organisms like protozoans, amoeba, etc.; single-celled beings with a nucleus. In sophisticated cells with a nucleus (eucaryotic cells), not only respiration, but even photosynthesis is more efficient, so the production of oxygen accelerated. Oxygen continued to build at an accelerating pace until 1% oxygen levels were obtained. The more oxygen accumulated in the atmosphere, the larger became the protective ozone layer (made of O₃ and formed from oxygen in the atmosphere). Ozone helped protect developing life from the harmful effects of the Sun's ultraviolet radiation. Then other life forms such as sponges, worms, and other organisms came to be.

Once oxygen levels of 1% were achieved, and an ozone layer developed, a seeming explosion in the development of different kinds of life forms occured. The Earth had entered what is known as the Cambrian age.

Click on image for full size version (43K JPG) Image from: Kentucky Coal Education Web Site

In the early Earth there was very little oxygen. 3.5 billion years ago there was only 0.01% oxygen in the atmosphere. 2.5 billion years ago there was only 0.1% oxygen in the atmosphere. At the top of Mt. Everest it is very hard to breathe because there is not enough oxygen. So imagine how hard it would be to breathe in the environment of the early Earth!

The formation of life on Earth played a very large role in the build up of oxygen in the environment. As early as 3.5 billion years ago, bacteria began to produce oxygen as a waste product of their activity. That oxygen reacted with iron in the ocean to make iron ore. Later, after the iron in the ocean was gone, and the making of iron ore was finished, about 2.5 billion years ago, enough oxygen accumulated for respiration (for animals which breathe oxygen) to begin in simple organisms, organisms like protozoans, amoeba, etc. Such organisms are sophisticated, they are single-celled beings with a nucleus! In sophisticated cells with a nucleus, not only respiration, but even photosynthesis is more efficient, so the production of oxygen in the Earths early environment accelerated. Oxygen continued to build at an accelerating pace until 1% oxygen levels were in place. The more oxygen accumulated in the atmosphere, the larger became the protective ozone layer (formed from oxygen in the atmosphere). Ozone helped protect developing life from the harmful effects of the Sun's ultraviolet radiation. Then other life forms such as sponges, worms, and other organisms came to be.

Once oxygen levels of 1% were achieved, and an ozone layer developed, there seemed to be enough oxygen present for the development of many different kinds of life forms, including dinosaurs. The Earth had entered what is known as the Cambrian age.

Click on image for full size version (43K JPG) Image from: Kentucky Coal Education Web Site

In the early Earth there was very little oxygen. At the top of Mt. Everest it is very hard to breathe because there is not enough oxygen. So imagine how hard it would be to breathe in the environment of the early Earth!

The formation of life on Earth played a very large role in the build up of oxygen in the environment. At first, bacteria began to produce oxygen as a waste product of their activity. That oxygen reacted with iron in the ocean to make iron ore. Later, after the iron in the ocean was gone, and the making of iron ore was finished, enough oxygen accumulated for simple organisms, organisms like protozoans, amoeba, etc. which are single-celled, to come to be. The more oxygen accumulated in the atmosphere, the larger became the protective ozone layer (formed from oxygen in the atmosphere). Ozone helped protect developing life from the harmful effects of the Sun's ultraviolet radiation. Then other life forms such as sponges, worms, and other organisms came to be.

Once there was enough oxygen to breathe, and an ozone layer developed, lots of different kinds of life forms, including dinosaurs, came to be. The Earth had entered what is known as the Cambrian age.