1. Earth’s Resources, Interactions, and Cycles
The Earth has renewable, nonrenewable, and inexhaustible resources.
Past events have led to the formation of many of the Earth’s resources.
The Earth’s different systems interact with each other.
Earth’s water, carbon and nitrogen are continually recycled.
Because of its atmosphere, soil, oceans, and living things, Earth’s physical characteristics are different from those of the moon.

2. Types of Natural Resources
A natural resource is something found in nature that people are able to use to meet their needs.
There are three types:
Renewable Resources
Nonrenewable Resources
Inexhaustible Resources

3. Renewable Resources
A renewable resource is something that can be replaced.
A renewable resource can be replaced by natural processed such as growth.
Renewable resources must be given time to renew itself.
Examples are forests, livestock, and food crops.

4. Nonrenewable Resources
A nonrenewable resource is formed over a very long period of time and cannot be replaced or renewed.
Examples are oil, coal, copper, and other minerals.
Once used, the nonrenewable resources cannot be replaced.

5. Inexhaustible Resources
An inexhaustible resource is in such a large supply that it cannot be used up by human activity.
Examples are energy from the sun, wind power, and heat from deep inside the Earth.

6. Soil Some soils can grow different crops better than others.
Because of this, each type of soil is a renewable resource.
To prevent erosion of the soil, farmers must practice soil conservation.
Examples of soil conservation—planting crops that hold the soil together, strip cropping, contour plowing, and terracing.

7. Gases
Since most of the atmosphere is made of nitrogen, this gas is almost inexhaustible.
As air pollution increases, the nitrogen becomes unusable.
Oxygen is a renewable resource. Plants produce oxygen during photosynthesis
If we reduce plant life by cutting down rainforests, we may reduce our oxygen.
The breathing of animals and the burning of materials create a gas called carbon dioxide.
Some scientists believe the large amount of of carbon dioxide now being produced has caused a heating up of Earth’s surface, known as global warming.

8. Water Water is needed by all living things to survive.
Fresh water is a valuable renewable resource. It is constantly replaced by the water cycle.
Water pollution threatens this water.

9. Rocks
Rocks above and below the Earth's surface contain many valuable minerals and other resources.
Because there is a great deal of sandstone and silicon, they might be considered inexhaustible.
However, because rocks and minerals cannot be replaced after they are taken from the ground, they are considered nonrenewable resources.

10. Fossil Fuels
Fossil fuels are burned to release large amounts of energy.
Coal is a brown or black rock formed from plants in forests or swamps 400 million years ago. When burned, coal releases the energy stored by plants from the sum millions of years ago.
Oil and natural gas were formed by very tiny one-celled plants and animals in the ocean.Over millions of years, heat and pressure changed their soft bodies to liquid oil and natural gas.

11. Fossil Fuels Continued
It takes millions of year for fossil fuels like oil and gas to form.
They can only be burned once.
Form this reason, they are important nonrenewable resources.
Some scientists fear their supply on Earth is being used at a faster rate than new energy resources can be found.

12. Interactions of Oceans and Land Forms
Rivers carry sediment from the land into the river.
Ocean currents take some of this sediment, accumulated over millions of years, to coastlines where it forms sandy beaches.
Tides come in twice each day as sea levels rise and fall.
Tides and waves erode the coastlines, wearing away rock and dissolving minerals.

13. Weather Patterns
Weather refers to conditions in the atmosphere at Earth’s surface—including temperature, rainfall or snowfall, and wind.
Climate is the typical weather of a place over a long period of time.
Weather results form the interaction of several systems—land features, energy from the sun heating the Earth’s atmosphere, and the Earth’s oceans.
The temperature stays cooler over lakes and oceans in the summer and warmer in the winter. This affects air flowing over these areas.

14. Rainfall Patterns
Because air cools as it rises over a mountain, the ocean side of a mountain often has heavy rainfall.
The air loses its moisture and becomes drier by the time it reaches the other side of the mountain, which has less rain.

15. Winds and Tornados
The uneven heating of the atmosphere by the sun create typical wind patterns.
Cold air sinks and warm air rises.
Tornadoes are high-speed winds that whirl in a funnel.
A tornado occurs when dry, cool air meets warm, humid air.

16. Tropical Hurricanes
Hurricanes occur in tropical regions in late summer and early fall when the ocean water is very warm.
The warm ocean water evaporates quickly and rises.
Air around the rising air column begins to spin at high speeds.
The hot air rises until it cools.
Then it releases energy and causes heavy rains, winds, and lightning.

17. The Earth’s Cycles
Cycles are processes that go through a series of steps in which the lat step leads back to the first step. Then the process begins all over again.
Important Cycles on Earth
The Water Cycle
The Carbon Cycle
The Nitrogen Cycle

18. The Water Cycle
The water cycle is the process by which the Earth’s water moves into and out of the atmosphere.
Steps in the water cycle
Evaporation
Condensation
Precipitation
Excess precipitation runs off into rivers, lakes and streams or is absorbed by the ground and becomes groundwater. Then some evaporates and the cycle begins again.

19. The Carbon Cycle
Carbon is continuously recycled among the atmosphere (as carbon dioxide), plants, and animals.
Steps in the carbon cycle
Algae and plants convert carbon dioxide from the air into sugars during photosynthesis.
Animals eat the stored carbon in the algae and plants; these animals return carbon dioxide to the air by breathing and during decay of their bodies and waste.
The remains of some plants and animals become part of the Earth’s crust by turning into coal, oil, or limestone.
Fossil fuels return carbon dioxide to the air when they are burned.

20. The Nitrogen Cycle
Although nitrogen is plentiful in the air, it is not in a form plants and animals can use.
Small organisms called bacteria turn the nitrogen into useful nitrates.
Look at the chart of the nitrogen cycle on page 168

21. The Nitrogen Cycle Steps
Waste products and remains of dead animals and plants are broken down by bacteria, leaving nitrates in the soil.
Some bacteria convert nitrogen compounds into nitrogen gas, which enters the atmosphere.
Plants obtain nutrients from the soil
Animals eat plants or other animals with nitrogen compounds.
Certain types of bacteria and algae convert nitrogen gas from the atmosphere into nitrogen compounds.
Animals eat these bacteria and algae, and convert their nitrates into their own nitrogen-based compounds

22. Human Activities
Problems can arise when human activities interfere with the water, carbon, and nitrogen cycles.
By burning fossil fuels, humans release more carbon dioxide than plants can use.
With the reduction of rainforests, the number of plants conducting photosynthesis is reduced.
When these things occur, the carbon cycle is changed and greater amounts of carbon dioxide build up in the atmosphere.

23. Comparing the Earth and Moon
The moon is a rocky sphere without water or air.
The Earth is made of rocky material that is mostly covered with water. Earth has an atmosphere.
Because the moon has no atmosphere, its surface is marked by craters from meteors.
Temperatures on Earth do not vary as greatly as they do on the moon, because our atmosphere holds in the heat and reduces the extremes in temperature.
Our atmosphere also traps water vapor and sends it back to Earth as rain or snow.