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