Atmosphere

• two components that changed earth's atmosphere:

  1. radiation from the sun - caused h2o to split, hydrogen going into space and oxygen in the atmosphere
  2. evolution of cynobacteria - began carrying out photosynthesis
• ozone layer (o3) protected terrestrial life from uv radiation
• at the present, the atmosphere is composed mainly of nitrogen and oxygen
• the atmosphere is divided into layers based on temperature: troposphere, mesosphere, thermosphere, and exosphere. it is separated by boundaries called "pauses"
• troposphere is the lowest layer. it contains 80 percent of the total mass in the atmosphere. most water vapor and weather-associated cloud types is found here.
• troposphere is 12 km, 9 km at poles; 17 km at equator. temperature decreases as altitude increases because of the atmosphere being thinner and absorbing less solar radiation. lowest part of troposhere (earth surface) is the warmest
• tropopause is found at the top of troposphere. the temperature stops decreasing in this level
• stratosphere is the second lowest layer. 12 km, 50 km altitude. temperature increases as altitude increases. this is because of the ozone absorbing uv rays and releasing some of it to the stratosphere. this is the layer where jet planes fly because it is free of clouds or forms of weather.
• the stratopause is on top of the stratosphere. this is where temperature stops increasing
• mesosphere is the third layer. 50, 80 km. altitude increases, temperature decreases. this layer protects earth from meteoroids. meteoroids burn up because of friction with air. they are called shooting star or burning meteors.
• upper mesosphere is the coldest region in atmosphere
• meteoroids that manage to reach earth are called meteorites
• mesopause is located on top of the mesosphere. temperature stops decreasing here
• thermosphere is the second highest layer. 80 to 700 km. temp increases as altitude increases. can rise to 1500 celsius.
• thermopause if found on top of thermosphere
• ionosphere is the portion of the thermosphere, 80 to 550 km. this only consists of highly-ionized gas. this gas is formed when uv rays knock electrons off nitrogen and oxygen
• the ions form bands or layers. the layers reflect ordinary radiowaves back into earth. this layer is called kennelly-heaviside layer
• at the poles, ions interact with air molecules to form an aurora. depending on their location, they may be called aurora borealis or northern lights, or aurora australis or southern lights