Unit 7 – The Atmosphere and Water Chapter 1, Section 1

Weather and the Atmosphere

• Weather - the condition of the Earth’s atmosphere at a particular time and place

• Atmosphere - the envelope of gases that surrounds the planet

Composition of the Atmosphere • Earth’s atmosphere is made up of: – Nitrogen – Oxygen – Carbon dioxide – Water vapor – Many other gases – Particles of solids and liquids

• Nitrogen (78% of gas in atmosphere) is the most abundant gas

– Each nitrogen molecule is made of two nitrogen atoms (N2)

• Oxygen (21% of gas in atmosphere) is the second most abundant gas – Used by plants and animals to release energy from their food – Also used to burn fuels

– Most oxygen molecules have two atoms (O2), but ozone has three oxygen atoms (O3)

• Carbon dioxide (0.04% of gas in atmosphere) – Used by plants to produce food – Given off by plants and animals when they release energy from their food – Given off when fuels are burned

• Water vapor – Is water in the form of a gas – Is invisible and varies greatly from place to place and time to time

• Particles – Made of solid and liquid particles of dust, smoke, salt, and other chemicals – Some can be seen, some cannot

• Importance of the Atmosphere • Earth’s atmosphere makes conditions on Earth suitable for living things – Keeps Earth warm – Protects living things from dangerous radiation from the Sun – Prevents Earth’s surface from being hit by most meteoroids Chapter 1, Section 3

• Layers of the Atmosphere • Scientists divide the Earth’s atmosphere into four main layers: troposphere, stratosphere, mesosphere, and thermosphere

• The troposphere – Inner or lowest layer of Earth’s atmosphere in which Earth’s weather occurs – About 9 to 16 km above Earth’s surface – For every 1 km increase in altitude, the temperature drops 6.5°C; top of troposphere is -60°C – Contains almost all the mass of the atmosphere • The stratosphere – Extends from top of troposphere to about 50 km above Earth’s surface – Contains the ozone layer (absorbs energy from the Sun; warming the upper stratosphere) • Protects Earth’s living things from the Sun’s dangerous ultraviolet radiation

• The mesosphere – Extends from top of stratosphere to 80 km above Earth’s surface – Protects Earth’s surface from being hit by most meteoroids (chunks of stone or metal from space) – Temperatures in outer mesosphere approach -90° C • The thermosphere – Is the outermost layer of the atmosphere – Extends from top of mesosphere outward into space – Air is very thin and hot (up to 1,800° C) – Divided into two layers: ionosphere and exosphere • Ionosphere – Is the inner layer of the thermosphere – Begins about 80 km above Earth’s surface and extends to 400 km – Ions here reflect radio waves back to Earth – Aurora borealis occurs here

• Exosphere – Is the outer layer of the thermosphere – Begins about 400 km above Earth’s surface – Communication satellites orbit Earth in the exosphere