42 Atmosphere and Climate-Mid

Atmosphere and Climate Written by Karen de Seve

Introduction Look up into the sky. There's a very thin, invisible shield surrounding Earth. It's called the atmosphere. This invisible shield makes life on Earth possible. It provides the air we breathe, the weather we experience, and the conditions needed for life on Earth. It protects us from the Sun's harmful rays. It controls the amount of Earth's heat that escapes into space. In this book you will learn about Earth's atmosphere, what it is made of, and how it makes life possible. You will learn the difference between weather over short and long periods of time. You'll also learn what makes up the atmosphere and how it is changing.

Earth's Invisible Shield The atmosphere is like a blanket. It protects and warms Earth's surface. The atmosphere rises more than 700 kilometers (430 mi.) above Earth's surface. It contains all the gases needed for life, such as nitrogen and oxygen. The atmosphere also contains small amounts of the gases argon, carbon dioxide (CO2), water vapor, and a few others. Oxygen is the gas that we need most. Without oxygen, life as we know it could not exist.

Gases are like all matter. They are made up of small, invisible particles called molecules. Gravity pulls the molecules toward Earth, packing them together. This blanket of gas molecules creates air pressure on all things within the atmosphere. At the bottom of the atmosphere—at sea level—air pressure is fairly high. Far up in the atmosphere, the air pressure is much lower.

You do not usually feel air pressure. The reason is because the pressure inside your body is about the same as the pressure outside your body. But when you take off in an airplane or drive up a mountain, you go higher in the atmosphere, where the air pressure is lower. As the outside air pressure drops, the air pressure inside your ears stays the same. As air exits your ears, you might hear a popping sound. Do You Know? Air pressure drops the higher you go. If you go high enough, the air molecules are very spread out. You will need extra oxygen in order to breathe.

Layers of Atmosphere Scientists have divided Earth's atmosphere into five layers. Each layer gradually changes into the next one. We live in the first layer—the troposphere— where Earth's weather forms and changes. The stratosphere is above the troposphere. This layer protects Earth from the Sun's radiation. The lowest part of the stratosphere is the ozone layer. This lower part is important to living things because it absorbs harmful ultraviolet rays from the Sun. Certain chemical gases that people release at Earth's surface threaten the ozone layer. These chemicals can float up into the stratosphere and break down ozone. The ozone is then less able to absorb ultraviolet rays. The mesosphere is the middle layer, in which most meteors burn up. Spacecraft orbit in the thermosphere. The exosphere is the outermost layer.