The Earth is surrounded by an ocean of gases we call the atmosphere. The atmosphere is important because it contains the air most living things breathe. ______ It even recycles water by returning it back to the Earth as rain. Without the atmosphere, life as we know it could not exist on Earth. The atmosphere extends about 600 kilometers (about 373 miles) above the suce of the Earth. Scientists discovered that the atmosphere is divided into layers, just like a layer cake.

• A. The layer of the atmosphere we live in is called the Troposphere (对流层).
• B. It also absorbs heat energy from the sun.
• C. Air temperature and air pressure are not the same all the way up through the Troposphere.
• D. Together they make up the remaining half of all the air that surrounds the Earth.
• E. Scientists have discovered that the ozone layer has gotten thinner due to pollution.
• F. It is also wise to wear sunglasses on bright days to guard against damage to our eyes.