Add to collection
  • + Create new collection
  • The Earth’s atmosphere1 is a layer of gases2 held close to its surface by gravity3. It plays a crucial role in supporting plant and animal life, helps to maintain a global average surface temperature4 of about 14°C, plays a major part in determining weather and climate, screens out harmful radiation5 from the Sun and acts as a buffer against meteorites.

    Rights: Fraser Gunn

    Aurora Australis over Lake Tekapo

    The colours of the Aurora Australis are caused by the reaction of the gases in our atmosphere with the solar winds that are emitted by the Sun.

    Composition of the atmosphere

    The principal components of the atmosphere are nitrogen6 (78%) and oxygen7 (21%), with the remaining 1% of the atmosphere being made up of argon8 (0.9%), carbon dioxide9 (0.037%) and trace amounts of other gases. The amount of water vapour10 in the atmosphere varies from 0–4% depending on temperature, pressure11 and location.

    Nitrogen, oxygen and carbon12 dioxide have very important associations with life:

    • Oxygen is exchanged between the atmosphere and life forms through the processes of photosynthesis13 and respiration14.
    • Certain types of soil bacteria15 can remove nitrogen from the atmosphere by ‘fixing’ it into nitrogen compounds usable by plants. This captured nitrogen is eventually released back into the atmosphere by bacterial decay of plant and animal material.
    • Carbon dioxide is an essential ingredient in photosynthesis and a major product of respiration.

    Average composition of the Earth’s atmosphere (to a height of 25 km)

    Gas

    Chemical formula

    Volume

    Nitrogen

    N2

    78.08

    Oxygen

    O2

    20.95

    Argon

    Ar16

    0.93

    Water vapour

    H2O

    0–4

    Carbon dioxide

    CO2

    0.041

    Neon17

    Ne

    0.0018

    Helium18

    He

    0.0005

    Methane19

    CH4

    0.00018

    Nitrous oxide20

    N2O

    0.00003

    Ozone21

    O3

    0.000004

    Vertical structure of the atmosphere

    About 80% of the atmosphere lies within 16 km of the Earth’s surface. On moving out from the surface, the atmosphere thins out until it merges with outer space.

    One practical way of placing a limit on the extent of the atmosphere was proposed by Theodore von Kármán (1881–1963), a Hungarian-American engineer involved in the aeroplane and spacecraft industries. He suggested that a limit be placed at 100 km above the Earth’s surface. It is at this altitude22 that an aircraft would need to fly at a speed equivalent to an orbiting spacecraft to give it enough lift23 to remain airborne. This arbitrary line is called the Kármán line

    Rights: The University of Waikato Te Whare Wānanga o Waikato

    Vertical structure of the atmosphere

    Vertical structure of the atmosphere showing four divisions based on temperature. If, alternately, the extent of gas mixing is used, the atmosphere can be divided into two main regions.

    Download a PDF version of this diagram.

    Layers based on temperature

    If regular temperature measurements are taken moving up through the Earth’s atmosphere, patterns emerge that allow the atmosphere to be divided into four layers – troposphere24, stratosphere25, mesosphere26 and thermosphere27 – with the boundaries between each given the suffix ‘-pause’. For example, the tropopause is the boundary between the troposphere and the stratosphere.

    Homosphere and heterosphere

    Another way of defining the structure of the atmosphere is based on the composition of the atmosphere. Below a height of about 80 km, the gases that make up the atmosphere are thoroughly mixed. This region is called the ‘homosphere’. Above this height, the gases separate out into bands related to their molecular masses with the heavier ones like oxygen and nitrogen present near the bottom. This region is called the ‘heterosphere’.

    Ozone layer and ionosphere

    Two other regions of the atmosphere often referred to are the ozone layer and the ionosphere28.

    The ozone layer is found within the lower part of the stratosphere from about 15–35 km. Although the actual concentration of ozone is very small, it plays a critical role in absorbing ultraviolet radiation, known as UV-C, that enters the atmosphere from the Sun.

    Rights: NASA

    Ozone layer

    The ozone layer is found within the lower part of the stratosphere. Although the actual concentration of ozone is very small, it plays a critical role in absorbing ultraviolet radiation, known as UV-C, that enters the atmosphere from the Sun.

    The ionosphere is the part of the atmosphere that is ‘ionised’ by incoming solar radiation29. It extends from about 85 km up to 600 km. The highly energetic UV radiation entering the Earth’s atmosphere can cause the removal of outer electrons from gas molecules30, creating positively charged gaseous ions31. This creates a shell of electrons mixed with charged atoms and molecules that surrounds the Earth. It is in this region of the atmosphere that auroras (natural light displays) occur.

    Related content

    Building Science Concepts: The air around us is a suite of resources for the early years to upper primary. It’s a great context for learning about the material and physical worlds.

    The activity Reading graphs uses a graph displaying the vertical structure of the atmosphere as a context for exploring and interpreting graphic representations.

    1. atmosphere: 1. The layer of gas around the Earth. 2. (atm) A non-SI unit of pressure equivalent to 101.325 kPa.
    2. gases: The state of matter distinguished from the solid and liquid states. Gases have the ability to diffuse readily and to become distributed uniformly throughout any container.
    3. gravity: The force attracting something towards the centre of Earth (or other large mass, like a moon or planet) – the reason that things fall to Earth.
    4. temperature: A measure of the degree of hotness or coldness of an object or substance. Temperature is measured with a thermometer calibrated in one or more temperature scales. Kelvin scale temperature is a measure of the average energy of the molecules of a body.
    5. radiation: Energy that is transmitted (radiates) from a source in the form of rays or waves or particles.
    6. nitrogen: A non-metal – symbol N, atomic number 7. Nitrogen is essential for life. It is a component of many molecules that make up cells, including DNA and proteins.
    7. oxygen: A non-metal – symbol O, atomic number 8. Oxygen is a gas found in the air. It is needed for aerobic cellular respiration in cells.
    8. argon: Argon is a noble gas with the symbol Ar and atomic number 18. It is the third most abundant gas in the Earth’s atmosphere.
    9. carbon dioxide: CO2 is a colourless, odourless, incombustible gas. It is a product of cellular respiration and combustion and is an essential component in photosynthesis.
    10. water vapour: The gas phase of water.
    11. pressure: The force per unit area that acts on the surface of an object.
    12. carbon: A non-metal element (C). It is a key component of living things.
    13. photosynthesis: A process that uses the energy from sunlight to convert carbon dioxide and water into carbohydrates, releasing oxygen as a byproduct. Photosynthesis occurs in the green parts of plants, in algae and in some microorganisms.
    14. respiration: Can mean either cellular respiration (the process by which cells create energy) or gas exchange (breathing).
    15. bacteria: (Singular: bacterium) Single-celled microorganisms that have no nucleus.
    16. augmented reality: A technology that adds digital elements to a live view of the real world.
    17. neon: Neon is a noble gas with the symbol Ne and atomic number 10. It is the second-lightest noble gas, after helium.
    18. helium: (He) A colourless, odourless inert gaseous element occurring in natural gas and with radioactive ores.
    19. methane: CH4, a gas that contributes to the greenhouse effect.
    20. oxide: A chemical compound made up of oxygen combined with at least one other element. Most of the Earth’s crust consists of oxides.
    21. ozone: Ozone is made up of three atoms of oxygen (O3). It is a highly reactive pale blue gas with a noticeable odour. Ozone forms a thin layer in the stratosphere. This layer protects life on Earth from ultraviolet rays. Ultraviolet radiation is a known cause of skin cancer.
    22. altitude: 1. The height of something, usually height above sea level. 2. In astronomy, the angular distance of a natural or artificial satellite above the horizon.
    23. lift: In aerodynamics, upward force produced by a difference in pressure due to airflow.
    24. troposphere: The lowest layer of the Earth’s atmosphere. We live in the troposphere. All weather happens in this layer.
    25. stratosphere: A layer in the atmosphere between 10 to 40 kilometres above the Earth’s surface where the temperature gradually rises from approximately -55 °C to 0 °C. The ozone layer is found in the stratosphere.
    26. mesosphere: A layer in the atmosphere between 50–80 km above the Earth’s surface. Meso is Greek for middle – the mesosphere is the middle atmosphere. The temperature gradually falls from 0 °C to -90 °C.
    27. thermosphere: A layer in the atmosphere between 80–700 km above the Earth’s surface. Thermo is Greek for heat. The temperature steadily increases, reaching around 70°C at 700 km.
    28. ionosphere: The region of the Earth’s upper atmosphere from about 85 km to 600 km made up of ionised gas (plasma).
    29. solar radiation: Radiant energy emitted by the Sun as a result of nuclear fusion reactions.
    30. molecule: Two or more atoms bonded together. The molecule of an element has all its atoms the same. The molecule of a compound has two or more different atoms.
    31. ion: An atom or group of atoms that has gained or lost electrons and has an electrical charge.
    Published 29 April 2014, Updated 24 July 2020 Referencing Hub articles
        Go to full glossary
        Download all

        atmosphere

      1. + Create new collection
      2. 1. The layer of gas around the Earth.

        2. (atm) A non-SI unit of pressure equivalent to 101.325 kPa.

        temperature

      3. + Create new collection
      4. A measure of the degree of hotness or coldness of an object or substance. Temperature is measured with a thermometer calibrated in one or more temperature scales. Kelvin scale temperature is a measure of the average energy of the molecules of a body.

        oxygen

      5. + Create new collection
      6. A non-metal – symbol O, atomic number 8. Oxygen is a gas found in the air. It is needed for aerobic cellular respiration in cells.

        water vapour

      7. + Create new collection
      8. The gas phase of water.

        photosynthesis

      9. + Create new collection
      10. A process that uses the energy from sunlight to convert carbon dioxide and water into carbohydrates, releasing oxygen as a byproduct. Photosynthesis occurs in the green parts of plants, in algae and in some microorganisms.

        augmented reality

      11. + Create new collection
      12. A technology that adds digital elements to a live view of the real world.

        methane

      13. + Create new collection
      14. CH4, a gas that contributes to the greenhouse effect.

        altitude

      15. + Create new collection
      16. 1. The height of something, usually height above sea level. 2. In astronomy, the angular distance of a natural or artificial satellite above the horizon.

        stratosphere

      17. + Create new collection
      18. A layer in the atmosphere between 10 to 40 kilometres above the Earth’s surface where the temperature gradually rises from approximately -55 °C to 0 °C. The ozone layer is found in the stratosphere.

        ionosphere

      19. + Create new collection
      20. The region of the Earth’s upper atmosphere from about 85 km to 600 km made up of ionised gas (plasma).

        ion

      21. + Create new collection
      22. An atom or group of atoms that has gained or lost electrons and has an electrical charge.

        gases

      23. + Create new collection
      24. The state of matter distinguished from the solid and liquid states. Gases have the ability to diffuse readily and to become distributed uniformly throughout any container.

        radiation

      25. + Create new collection
      26. Energy that is transmitted (radiates) from a source in the form of rays or waves or particles.

        argon

      27. + Create new collection
      28. Argon is a noble gas with the symbol Ar and atomic number 18. It is the third most abundant gas in the Earth’s atmosphere.

        pressure

      29. + Create new collection
      30. The force per unit area that acts on the surface of an object.

        respiration

      31. + Create new collection
      32. Can mean either cellular respiration (the process by which cells create energy) or gas exchange (breathing).

        neon

      33. + Create new collection
      34. Neon is a noble gas with the symbol Ne and atomic number 10. It is the second-lightest noble gas, after helium.

        oxide

      35. + Create new collection
      36. A chemical compound made up of oxygen combined with at least one other element. Most of the Earth’s crust consists of oxides.

        lift

      37. + Create new collection
      38. In aerodynamics, upward force produced by a difference in pressure due to airflow.

        mesosphere

      39. + Create new collection
      40. A layer in the atmosphere between 50–80 km above the Earth’s surface. Meso is Greek for middle – the mesosphere is the middle atmosphere. The temperature gradually falls from 0 °C to -90 °C.

        solar radiation

      41. + Create new collection
      42. Radiant energy emitted by the Sun as a result of nuclear fusion reactions.

        gravity

      43. + Create new collection
      44. The force attracting something towards the centre of Earth (or other large mass, like a moon or planet) – the reason that things fall to Earth.

        nitrogen

      45. + Create new collection
      46. A non-metal – symbol N, atomic number 7. Nitrogen is essential for life. It is a component of many molecules that make up cells, including DNA and proteins.

        carbon dioxide

      47. + Create new collection
      48. CO2 is a colourless, odourless, incombustible gas. It is a product of cellular respiration and combustion and is an essential component in photosynthesis.

        carbon

      49. + Create new collection
      50. A non-metal element (C). It is a key component of living things.

        bacteria

      51. + Create new collection
      52. (Singular: bacterium) Single-celled microorganisms that have no nucleus.

        helium

      53. + Create new collection
      54. (He) A colourless, odourless inert gaseous element occurring in natural gas and with radioactive ores.

        ozone

      55. + Create new collection
      56. Ozone is made up of three atoms of oxygen (O3). It is a highly reactive pale blue gas with a noticeable odour. Ozone forms a thin layer in the stratosphere. This layer protects life on Earth from ultraviolet rays. Ultraviolet radiation is a known cause of skin cancer.

        troposphere

      57. + Create new collection
      58. The lowest layer of the Earth’s atmosphere. We live in the troposphere. All weather happens in this layer.

        thermosphere

      59. + Create new collection
      60. A layer in the atmosphere between 80–700 km above the Earth’s surface. Thermo is Greek for heat. The temperature steadily increases, reaching around 70°C at 700 km.

        molecule

      61. + Create new collection
      62. Two or more atoms bonded together. The molecule of an element has all its atoms the same. The molecule of a compound has two or more different atoms.