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UNSW : UNSW Atmosphere Study Guide
Atmosphere Study Guide 3 The Earth’s atmosphere WHAT IS THE EARTH’S ATMOSPHERE? The Earth’s atmosphere is a large blanket of air that surrounds our planet, protecting us from the harsh conditions of space and allowing life as we know it to survive. The atmosphere stretches out around 600 km from the Earth’s surface and changes significantly in composition the further up you go. The atmosphere is made up of 78% nitrogen, 21% oxygen and also contains little bits of argon, carbon dioxide, ozone and other trace gases. Beyond the atmosphere, hydrogen and helium are the prime components that make up space. We find out about the atmosphere using technology such as weather balloons and satellites, and by studying the concentration of gases in ice samples, ancient rocks and the ocean. There are four distinct layers of the atmosphere: the troposphere, the stratosphere, the mesophere and the thermosphere. All of these have very distinct properties that will be described in more detail throughout the notes. Troposphere This is the section closest to Earth and goes up to about 12 km. This is where most of the weather occurs, such as clouds, and it makes up 80% of the entire atmosphere’s weight. Temperatures in the troposphereaverage around –55̊C and it gets colder the higher up you get. Stratosphere The stratosphere extends from around 12 km to 50 km and contains the ozone layer, which absorbs ultraviolet (UV) light. This feature makes this section of the atmosphere slightly warmer, and the temperature is around –3̊C. Mesosphere This is the coldest place in the atmosphere, stretching from 50 km to 100 km above the planet’s surface and reaching temperatures as low as –90̊C. Thermosphere This layer of the atmosphere soaks up most of the dangerous forms of solar radiation, and stretches from the top of the mesosphere to 600 km above sea level. It’s a near vacuum and would feel very cold, but some of the gases can reach up to 2,500̊C because of the action of cosmic rays coming from the Sun. Without our atmosphere, Earth would just be a tiny rock floating through the dangerous conditions of space. The Earth’s atmosphere is one of the things that makes our planet so unique, and is one of the main reasons that life has developed here so successfully. But what exactly is the atmosphere and how can we protect it? WHAT DOES IT DO? The atmosphere, which is held in place by the Earth’s gravity, protects us from extreme radiation from the Sun. It also controls the fluctuations in temperature on Earth – if we had no atmosphere, the nighttime would be deadly cold and temperatures in general would be more extreme. The atmosphere also contains all of our weather, such as the wind and rain. This weather is controlled by differences in temperature and moisture in varying regions. These differences can result in variations in pressure, which can result in storms or, in extreme cases, cyclones and tornadoes. While ‘weather’ is the term used for the temperature and conditions from day to day, ‘climate’ refers to the average conditions over a long period of time. The atmosphere also affects our climate and as a result of human activity and its impact on the atmosphere, Earth’s climate is now changing. Without the atmosphere, the planet’s temperature would be significantly more extreme and we would have no weather. Timeline A glimpse at how the atmosphere, and our understanding of it, has changed over time. 4.6 billion years ago The Earth’s atmosphere only contains 21% oxygen, mostly in the form of water vapours. Only organisms that don’t need oxygen to generate energy in their body could survive in this atmosphere. 2.4 billion years ago The Great Oxygenation Event occurs and the first free- standing oxygen appears in the atmosphere (as O2). Without this event, most of the life on Earth today wouldn’t have evolved. 1800 – 1870 The first global industrial revolution occurs, resulting in an increase in CO2 emissions. The average global temperature is about 13.6̊C and the level of CO2 in the atmosphere has been around 290 parts per million (ppm) since the last glacial period. 1896 A Swedish scientist, Svante Arrhenius publishes the first calculation of global warming from human CO2 emissions. Backgrounder WIKIMEDIA