Grade 6: Earth Science 15.1. CHARACTERISTICS OF THE ATMOSPHERE What is the atmosphere? Definition: A mixture of gases that surround the Earth. Effects of the Atmosphere: •Supports life. Contains all the gases needed for humans and other living organisms to breathe and survive. •Protects life on Earth from the sun’s damaging rays. Nitrogen: The most common atmospheric gas. Makes up 78% of the atmosphere. Oxygen: Makes up approximately 21% of the atmosphere. This is the gas we breathe and is necessary for most life on Earth to survive. Other gases: Carbon dioxide, methane, argon and many other gases also form part of the atmosphere. Carbon dioxide is a greenhouse gas. Water Vapour: Together with other gases, water vapour makes up approximate 1% of the atmosphere. May turn into rain or snow depending on weather conditions. Small Particles: The atmosphere contains many of these particles, including dust, sea salt, dirt, smoke and volcanic ash. Atmospheric Pressure What is Air Pressure? The measure of the force with which air pushes on a surface. •Close to the Earth’s surface, at sea level (low altitude), more air is above you. •This increases pressure at lower altitudes. •Further away from sea level (higher altitude), less air is above you. •This decreases pressure at higher altitudes. Atmospheric Composition affects Temperature •As altitude increases the temperature also changes. Why? •This is due to different gases present in each layer of the atmosphere. •Some gases absorb solar energy. Layers of the atmosphere with these gases are warmer. •Other layers of the atmosphere have less of these gases. These are cooler. Layers of the Atmosphere The atmosphere is divided into 4 layers: •Troposphere •Stratosphere •Mesosphere •Thermosphere Layers of the Atmosphere Troposphere: •Lies next to the Earth’s surface. •All life forms, carbon dioxide, water vapour, weather conditions and clouds occur here. •Is constantly changing. Stratosphere •Contains the ozone layer. •Is extremely cold (except for where the ozone layer occurs) and has little water vapour. •The Ozone layer absorbs ultra-violet rays. Layers of the Atmosphere Mesosphere: •The middle layer of the atmosphere. •Is the coldest layer. •Temperatures decrease as altitude increases. Thermosphere: •Uppermost layer of the atmosphere. •Has the highest temperature of all the layers of the atmosphere. •Is the least dense of the layers.