1. Warm Up 3/4/08
True or False: The seasons are caused by changes in Earth’s distance from the sun.
False
Does land or water heat more rapidly?
Land heats more rapidly
If you move from sea level to a location in the mountains, how will the temperature change?
It will get colder

2. Atmosphere Characteristics
Chapter 17, Section 1

3. Weather
No other planet in our solar system has an atmosphere with the exact mixture of gases or the moisture conditions and heat needed to sustain life as we know it
Weather is constantly changing, and it refers to the state of the atmosphere at any given time and place
Climate is based on observations of weather that have been collected over many years
Climate helps describe a place or region
The most important measurable properties of weather and climate are air temperature, humidity, type and amount of precipitation, air pressure, and the speed and direction of wind

4. Weather

5. Concept Check How does weather differ from climate?
Weather changes constantly, but climate is based on patterns of weather that have been observed over years. Climate helps describe a place or region.

6. Composition of the Atmosphere – Major Components
The composition of the atmosphere has changed dramatically over Earth’s nearly 4.6 billion year history
The atmosphere is thought to have started from gases that were emitted during volcanic eruptions
Air is a mixture of different gases and particles, each with its own physical properties
Two gases—nitrogen and oxygen—make up 99% of the volume of clean, dry air

7. Gases Composing Clean, Dry Air

8. Composition of the Atmosphere – Variable Components
Important materials that vary in the air from time to time and place to place include water vapor, dust particles, and ozone
Water vapor is the source of all clouds and precipitation.
Movements of the atmosphere allow a large quantity of solid and liquid particles to be suspended within it
Ozone – a form of oxygen which combines three oxygen atoms into each molecule (O3)
We breath oxygen which has two atoms per molecule (O2)
Ozone is concentrated 10 to 50 kilometers above Earth’s surface
If ozone did not filter most UV radiation and all of the sun’s UV rays reached the surface of Earth, our planet would be uninhabitable for many living organisms

9. Composition of the Atmosphere – Human Influence
Air pollutants are airborne particles and gases that occur in concentrations large enough to endanger the health of organisms
Primary pollutants, are emitted from identifiable sources
Secondary pollutants are not emitted directly into the air, they form in the air when reactions take place among primary pollutants and other substances
Reactions triggered by strong sunlight are called photochemical reactions

10. Primary Pollutants

11. Concept Check What are secondary pollutants?
Secondary pollutants are pollutants that form when reactions take place among primary pollutants and other substances.

12. Height and Structure of the Atmosphere
The atmosphere thins as you travel away from Earth until there are too few gas molecules to detect
Atmospheric Pressure – weight of the air above (~1000 millibars at sea level)
The higher you go in the atmosphere, the less air pressure there will be
The atmosphere can be divided vertically into four layers based on temperature (troposphere, stratosphere, mesosphere, and thermosphere)

13. Atmospheric Pressure Variation with Altitude

14. Layers of the Atmosphere
Troposphere – bottom layer of atmosphere, temperature decreases with an increase in altitude (~0-12 kilometers)
This layer essentially has all the weather phenomenon
Stratosphere – temperatures gradually increase due to concentration of ozone (~12-50 km)
Mesosphere – temperatures again decrease with altitude, going as low as -90ºC (~50-80 km)
Thermosphere – no well defined boundary, temperatures increase, due to short-wave solar radiation being absorbed

15. Thermal Structure of the Atmosphere

16. Earth-Sun Relationships
Solar energy is not evenly distributed over Earth’s surface, but varies with latitude, time of day, and season of the year
It is this unequal distribution of heat which creates winds and drives the ocean’s currents
Seasonal changes occur because Earth’s axial position relative to the sun continually changes as it travels along its orbit
If the axis were not tilted, we would not have seasonal changes

17. Summer and Winter Solstice occur when Earth’s tilt is pointed away from the sun
The Autumnal and Spring Equinoxes occur when the sun’s vertical rays strike the equator (Earth not tilted towards or away from the sun)
The length of daylight compared to darkness also is determined by Earth’s position in orbit

18. Sun Rays Striking Earth

19. Earth-Sun Relationships

20. Solstices and Equinoxes

21. Concept Check In which direction does Earth’s axis point?
Earth’s axis points toward the North Star.

22. Assignment Read Chapter 17 (pg. 476-493)
Do Chapter 17 Assessment #1-30 (pg )
Print out “Investigation 17A – Determining How Temperature Changes with Altitude”

23. Cool Down Why do seasonal changes occur?
Seasonal changes occur because Earth’s axis is tilted. Earth’s orientation to the sun continuously changes as it travels along its orbit.
Explain what would happen to air temperatures in the troposphere if carbon dioxide were removed from air.
Because carbon dioxide absorbs heat from Earth efficiently, air temperatures would decrease if it were removed from the troposphere.
What is one new thing you learned today? Explain.