by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
UNSW : UNSW Atmosphere Study Guide
Atmosphere Study Guide 22 The only one of its kind in the Solar System, the Earth’s atmosphere protects us from the dangerous conditions of space. Cosmos finds out what makes our planet’s safety blanket so unique. Safety blanket 200 0 400 600 Thermosphere Mesosphere Stratosphere Troposphere km sources:theearth’satmosphere:itsphysicsanddynamics,bykshudiramsaha;theearthsystem,bydavidlaing;anoceanofair,bygabriellewalker;australianantarcticdivision;nasa;u.s.nationalcentreforatmosphericresearch THE COMFORTING EMBRACE of the Earth’s atmosphere protects us from the harsh conditions of space and tempers the relentless radiation from the Sun. Composed of 78% nitrogen, 21% oxygen, and peppered with argon, carbon dioxide, ozone and other trace gases, Earth’s atmosphere is like no other in the Solar System. It is composed of four key layers that are distinguished by their thermal characteristics, chemical composition, movement and density. Even though each is distinct, “the whole globe is interconnected, and the atmosphere is a really dynamic and interwoven entity,” says Andrew Klekociuk, an atmospheric scientist with Australian Antarctic Division. UPPER ATMOSPHERE Thermosphere • 200-600 km above sea level. • 99.9% of the volume of the atmosphere. • A near vacuum. It would feel very cold, but the few widely distributed gas molecules can reach up to 2,500°C through the action of cosmic rays. • Composed of two layers: the ionosphere and the magnetosphere • Ionosphere is the ‘big brother’ of the ozone layer, and soaks up the most dangerous forms of solar radiation, such as X-rays and gamma radiation. The International Space Station orbits just above this sphere and is reinforced to protect astronauts against cosmic rays. • The ionosphere gets its name from the abundance of charged particles in the layer. These create the northern and southern lights, or auroras. Auroras occur at 100-200 km above us, and are caused by charged particles colliding with those in the magnetosphere; the colour varies depending on the elements encountered. • The thermosphere also has a number of distinct layers of metal ions, which form naturally between altitudes of 87 and 110 km. Layers of sodium, calcium, potassium and iron form from the constituents of meteors that pass through the layer. MIDDLE ATMOSPHERE Mesosphere • 50-100 km above sea level. • Coldest place on Earth, with an average temperature of -90°C. • Occasionally ice clouds form in this region, at altitudes of around 85 km. They are so high in the atmosphere that they can still be seen illuminated after sunset from the Earth’s poles. The clouds are created by a process distinct to the mesosphere and are larger than low- and mid-level clouds. Stratosphere • Starts at end of troposphere and goes up to around 50 km above sea level. • The ozone layer is found here and is a minefield of five billion tonnes of reactive ozone molecules. Ozone molecules absorb the energy of the Sun’s ultraviolet radiation (UV), which makes them break apart and reform. Without this layer, the UV, which damages DNA and causes cancer, would pose much bigger threat to life. • Temperature in the region rises to -3°C due to the ozone layer absorbing this UV radiation. • The ozone layer is easily degraded. In 1976, scientists discovered a hole in this layer above Antarctica, due to 40 years of chlorofluorocarbon (CFC) emissions from industry and aerosols. In 1987, the Montréal Protocol to ban CFCs was enacted, dramatically lowering CFCs in the atmosphere. LOWER ATMOSPHERE Troposphere • Starts at the planet’s surface and goes up to an average of 12 km above sea level (range: 5-16 km). This is the thinnest layer. • Location of most weather. Low-level clouds below 2 km, mid-level to 6 km. • 80% of the weight of entire atmosphere. • Where nearly all life, commercial aircraft (up to 10 km), skydivers (8 km) and hot air balloons (2 km) are found. • Warmest layer because of sunlight reflected from the surface, but temperature falls steadily with altitude, and reaches a low of -75°C. – Melanie Macfarlane Illustration Andrew Davies Explain (article one) NASA An illustration of the Earth’s atmosphere from space.