Atmosphere: All the gases surrounding Earth
§ 4 billion years ago
§ Methane- CH4 - A combination of Carbon and Hydrogen
§ Ammonia- NH3 – A combination of Nitrogen and Hydrogen
§ Both are deadly to all life
§ A great deal of water vapor
§ Water vapor holds in heat
§ Sunlight triggered chemical reactions
§ Much hydrogen escaped because it was so light
§ Nitrogen became the most abundant gas
§ Carbon from the methane combined with oxygen to
form Carbon Dioxide (CO2)
§ Oxygen in the upper atmosphere formed ozone (O3)
§ Ozone is Earth’s protective layer – it protects Earth from
the sun’s ultra violet radiation
§ Ozone is a form of oxygen
After 4 billion years our present atmosphere developed with the gases necessary to support all life. These gases are:
§ Nitrogen (N2) – 78%
§ Oxygen (O2) – 21 %
§ Water Vapor (H2O) and Carbon Dioxide (CO2) – 1%
§ Trace Gases – All together make up less than 1%
These gases are arranged in layers according to major changes in temperature.
As you travel upward in altitude through the layers air pressure decreases.
Air pressure is the downward push of the air on Earth’s surface.
Gravity is the force that holds all the layers of the atmosphere together.