| A | B |
|---|
| atmosphere | mixture of gases that surround earth |
| nitrogen N2 | majority gas in atmosphere (79%) |
| oxygen O2 | gas needed for cellular respiration (21%) |
| water vapor | gaeous form of water |
| air pressure | force caused by layers of air pushing down on the earth's surface |
| troposphere | bottom layer that contains weather and life |
| stratosphere | layer just above the troposphere; contains ozone layer |
| mesosphere | above stratosphere; coldest layer |
| ionosphere | contains ions that reflect radio waves; between mesosphere & thermosphere |
| thermosphere | layer with highest temperatures |
| ozone layer O3 | stratospheric area that has a high concentration of ozone (O3) |
| exosphere | least dense area; contains hydrogen and helium gases; exits into space |
| aurora borealis | nothern lights caused by excitation of ions in the northern ionosphere |
| aurora australis | southern lights caused by excitation of ions in the southern ionosphere |
