| A | B |
|---|
| atmosphere | a mixture of gases that susrrounds a planet, such as Earth |
| nitrogen | the most abundant gas in the atmosphere. It is released into the atmosphere by volcanic eruptions and when dead plants and dead animals decay. |
| oxygen | the second most common gas in the atmosphere, is produced by plant-like protists and plants. |
| atmospheric pressure | a measure of the force per unit area of air molecules in the atmosphere at a given altitude |
| altitude | the height of an object above the Earth's surface. |
| troposphere | the lowest layer of the atmosphere |
| stratosphere | the atmospheric layer above the troposphere |
| ozone | a gas molecule that is made up of three oxygen atoms and that absorbs ultraviolet radiation from the sun. |
| mesosphere | the coldest layer of the atmosphere. |
| thermosphere | the uppermost layer of the atmosphere. |
| ionosphere | part of the thermosphere with electrically charged particles (called ions). |
| air | a mixture of gases that make up Earth's atmosphere |
| barometer | an instrument that measures atmospheric pressure |
| exosphere | the region of the atmosphere that begins at about 500 kilometers above Earth and extends into space, the location of the orbits of satellites |
| specific heat | the amount of energy needed to raise the temperature of 1 gram of a substance by 1 degree Celsius |
| rotation | the motion of Earth spinning on its axis. one rotation is called a day |
| revolution | the motion of Earth moving around the Sunl one revolution is called a year |
| calendar | the means of keeping track of all the days in a year |
| year | the amount of time it takes Earth to complete one revolution around the Sun, 365.25 days |
| day | the amount of time it takes the Earth to spin one time on its axis (rotate) |
| month | the amount of time it takes the Moon to revolve one time around the Earth |
| leap year | a year that has an extra day in February, it happens every 4 years. |
