The Early Atmosphere

The atmosphere is a layer of gas around the Earth. Air is a mixture of gases. It is most dense at sea-level and thins out as we rise through the layer of atmosphere called the troposphere. 

The Earth formed about 4600 million years ago. The ozone layer protects us from the Sun's most harmful ultraviolet rays. The atmosphere is maintained by nature recycling substances in living things. All living things depend upon oxygen,…