Atmosphere
- The atmosphere forms a protective blanket around Earth and makes it a habitable planet for life. It is the air we breathe and plays a key role in the weather we all like to complain about.
- The atmosphere encompass all the gases that swirl around the Earth.
- The blue colour of the sky is because of dispersion and absorption of the Sun's radiation by molecules in the atmosphere.
- The red colour in the morning and the evening is because of particles, such as dust, smoke or ash.
LEARNING ACTIVITY - SHARE an image of a sunset around you.
If we told you earth has had two atmospheres, would you believe us?
- Earth has had two atmospheres
- True
- Correct. The first was lost when a small planet collided with Earth to form the Moon. The second atmosphere was outgased from the interior of Earth. It was retained by gravity and protected from solar winds by the Earth’s magnetic field.
- False
- Incorrect. Had to believe right? Try again and learn why the earth has had two atmospheres.
Early Earth’s atmosphere would be toxic to us. It was mainly made up of nitrogen, carbon dioxide, methane, hydrogen and some sulfur dioxide with almost no oxygen.
Early life began to change the atmosphere by using gases such as methane, sulfur dioxide, and carbon dioxide and expelling oxygen.
The Earth’s atmosphere has evolved with life so now the atmosphere is nearly 21% oxygen. In comparison CO2 in the atmosphere is tiny (0.04%) and methane makes up even less (0.00018%). None of these volume estimates take water vapour into account.
The amount of water vapour varies a lot from place to place, time of day and season. There is more water near the equator and most of it is invisible water vapour that we experience as humidity, even though the sky is clear.
What makes up the Atmosphere
Scientist divide the atmosphere into spheres that encircle the Earth based on composition and temperature
- Most (75%) of the mass of the atmosphere is in the troposphere.
- Mass is about 5.14 x 1018 kg (=514,000,000,000,000,000 kg*)
- estimate from Trenberth & Guillemot, 1994 Total mass of the atmosphere, Journal of Geophysical Research, 99, 23,079-23,088
Atmosphere on the move
Rotation of the Earth, heat from the sun and cooling where there is no sun all help create the circulation systems that move the Earth’s atmosphere. The image above shows the overall circulation of the atmosphere. Known and exploited by sailors.
Air currents can move gases, microbes, and particles all around the Earth so the air you are breathing in today may have been halfway around the world a few days ago
Ash from Chile's Puyehue-Cordon-Calle volcanic complex eruption in 2011 circumnavigated the world twice in the southern latitudes and caused the closure of airports in southern Australia.
How the Atmosphere protects us
The atmosphere blocks out all gamma rays, X-rays and much of the Ultraviolet (short wavelength radiation) that is harmful to life (see image above). Only visible light, limited Ultraviolet and long wavelength called radio waves make it to the Earth's surface. The most important absorbing gases are O3 for absorbing Ultraviolet radiation, and CO2 and H2O for absorbing Infrared Red radiation. Most meteorites burn up in the mesosphere: Very few actually land on Earth’s surface.
