<p> 1</p><p>THIRD PLANET FROM THE SUN : THE EARTH</p><p>Our atmosphere, or air, makes it possible for life on Earth.</p><p>Earth's Atmosphere</p><p>The atmosphere is a mixture of nitrogen (78%), oxygen (21%), and other gases (1%) that surrounds Earth. </p><p>High above the planet, the atmosphere becomes thinner until it gradually reaches space. It is divided into five layers. Most of the weather and clouds are found in the first layer. </p><p>The atmosphere is an important part of what makes Earth livable. It blocks some of the Sun's dangerous rays from reaching Earth. It traps heat, making Earth a comfortable temperature. And the oxygen within our atmosphere is essential for life. </p><p>Over the past century, greenhouse gases and other air pollutants released into the atmosphere have been causing big changes like global warming, ozone holes, and acid rain. </p><p>Layers of the Earth's Atmosphere</p><p>The atmosphere is divided into five layers. It is thickest near the surface and thins out with height until it eventually merges with space. </p><p>1) The troposphere is the first layer above the surface and contains half of the Earth's atmosphere. Weather occurs in this layer. Close to Earth's surface, oxygen is essential to life, because it allows us to breathe.</p><p>2) Many jet aircrafts fly in the stratosphere because it is very stable. The stratosphere has the ozone layer that absorbs harmful rays from the Sun. 2 High in the stratosphere, some of the oxygen has changed over time to ozone. The ozone layer filters out the Sun's harmful rays. Recently, there have been many studies on how humans have caused a hole in the ozone layer. Humans are also affecting Earth's atmosphere through the greenhouse effect. Increasing concentrations of gases like carbon dioxide are trapping heat as it is radiated from the Earth. This is highly likely to be the cause of global warming.</p><p>Various chemicals that humans release into the atmosphere can destroy ozone in the stratosphere. This has caused a thinning of the ozone layer in recent years, and even holes in the ozone layer over Earth's poles.</p><p>3) The next layer is the mesosphere. Meteors or rock fragments burn up in the mesosphere.</p><p>4) The thermosphere is a layer with auroras like the ones at the North Pole. It is also where the space shuttle orbits. </p><p>5) The atmosphere merges into space in the extremely thin exosphere. This is the upper limit of our atmosphere. Weather</p><p>Weather is the state of the atmosphere at a given time and place. Most weather takes place in the troposphere, the lowest layer of the atmosphere.</p><p>Weather is measured and described in a variety of ways by meteorologists. Meteorologists are scientists who study and predict weather. </p><p>Air temperature and pressure are in weather. Rain and snow are types of precipitation. The strength and direction of wind, and the types of clouds are all described in a weather report. </p><p>Weather changes each day because the air in our atmosphere is always moving. Our atmosphere collects and moves energy from the Sun. In most places in the world, the types of weather events also change throughout the year as seasons change. </p><p>3</p>