A1-2 Composition – Permanent Gases

The Earth’s atmosphere is composed primarily of two gases: nitrogen and oxygen. Together these two gases make up 99% of the Earth’s atmosphere.

This pie chart illustrates the major components of the Earth’s atmosphere.

Nitrogen: At 78.1%, nitrogen is by far the largest component of the Earth’s atmosphere. Although nitrogen is not a component of breathing, it is, nonetheless, an integral part of the life cycle of all organisms. Nitrogen, for example, is a requirement for the manufacture of protein in cells, and for the copying of hereditary material (i.e. DNA).

Oxygen: Oxygen is a fundamental component of respiration for all living organisms. Oxygen is produced primarily through photosynthesis. Oxygen makes up 20.9% of the Earth’s atmosphere.

The relative proportions of nitrogen and oxygen are fairly stable over time. Since their proportions do not change, nitrogen and oxygen are considered to be permanent gases.

What Do You Think?

Vegetation and the Production of Oxygen

This forest in the Amazon is a significant producer of oxygen for the world.

The main view panel to the right shows a global view of the Normalized Difference Vegetation Index (NDVI). This view, determined by satellites, shows the extent and concentration of live, green vegetation on land.

  1. Why do you think NDVI is important?
    2. It is important because it highlights land-based areas of the Earth that are significant centers of oxygen production through photosynthesis.
  • Click here to add in the NDVI scale, as well as the equator for reference.
  1. What color corresponds to areas with the densest vegetation?
    2. Dark green corresponds to areas with the densest vegetation.
  • Rotate the Earth and examine how vegetation is distributed across the planet.
  1. What parts of the Earth have the densest vegetation, and are, therefore, key areas of oxygen production? What kind of vegetation do you think is present in these areas?
    2. Equatorial regions have the densest vegetation. Tropical rain forests dominate these areas.
  • Rotate the Earth and locate areas that have an NDVI color of white.
  1. What geographical areas do you think correspond to an NDVI color of white?
    2. The NDVI color of white corresponds to areas of snow and ice (i.e. Antarctica, the Arctic, and mountainous areas).
  • Rotate the Earth and locate areas that have an NDVI color of brown.
  1. What geographical areas do you think correspond to an NDVI color of brown?
    2. The NDVI color of brown corresponds to desert areas. (Click here to see a labeled view of some of these areas.)

  2. Is land-based vegetation the major source of the world’s oxygen? What do you think?
    3. Contrary to popular belief, the majority of the world’s oxygen is not produced by land-based green vegetation. Over half of the world’s oxygen is produced by single-celled plant organisms called phytoplankton that live on or near the ocean’s surface. (Click here to see both the land-based NDVI distribution, and the water-based phytoplankton distribution.)

Did You Know?

Why Is the Sky Blue?

Gases in the Earth’s atmosphere scatter blue light more than light of any other color. This results in the characteristic blue color of the sky.

Scattered light in the atmosphere produces a brilliant blue sky as seen here in Kananaskis, Alberta, Canada.
Math Link

Comparing Earth and Mars

Compare the major atmospheric components of Earth and Mars. Go to Math Link…