43 Atmosphere and Climate-High

Atmosphere and Climate Written by Karen de Seve

Introduction The next time you go outside, take a moment to look up into the sky. You won't see it, but there's a very thin, invisible shield surrounding and protecting 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. The atmosphere protects us from the Sun's harmful rays, and it controls the amount of Earth's heat that escapes into space. It even protects us from objects such as meteors falling from 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 and climate, as well as what makes up the atmosphere and how it is changing.

Earth's Invisible Shield The atmosphere acts like a blanket, protecting and warming Earth's surface. It rises more than 700 kilometers (430 mi.) above Earth's surface and contains all the gases needed for life. The atmosphere is a mixture of 78 percent nitrogen and 21 percent oxygen. There are also small amounts of argon, carbon dioxide (CO2) water vapor, and a few other gases, but it is oxygen that we need most. Without oxygen, life as we know it could not exist.

Gases, like all matter, are made up of small, invisible particles called molecules. These molecules are pulled toward Earth by the force of gravity. Gravity pulls down on the air molecules, so air close to the ground is denser than air close to outer space. The blanket of gas molecules presses down, creating air pressure on all things within the atmosphere. Air at the top of the atmosphere is about a million times less dense than the air at sea level. This means the molecules are spread farther apart. As a result, the air pressure high in the atmosphere is much lower.

You do not normally feel the pressure of the atmosphere because the pressure inside your body is in balance with the outside pressure. But if you go higher in the atmosphere, the air pressure drops, while the pressure inside your body stays the same. That's why you feel your ears pop when you take off in an airplane or drive up a mountain. As the outside air pressure drops, the air pressure inside your ears stays the same. As air escapes, it makes 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, so you will need extra oxygen in order to breathe.

Layers of Atmosphere Scientists have divided the atmosphere into five layers. Each layer is a sphere that surrounds Earth. One layer gradually changes into another. We live in the first layer of the atmosphere —the troposphere. Earth's weather forms and changes within the troposphere. The second layer— the stratosphere— acts like a filter. The lowest part of the stratosphere, called the ozone layer, 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. This leaves the living things on Earth's surface vulnerable. The mesosphere is the layer in which most meteors burn up. Spacecraft orbit in the thermosphere. The exosphere is the outermost layer.