Unit 11 lớp 11

SOURCES OF ENERGY

The natural environment includes all natural resources that are necessary for li8fe: the air, the ocean, the sun, and the land. Because they are vital for life, these resources must be protected from pollution and conserved. Ecologists study their importance and how to use them carefully.

According to ecologists, resources are divided into two groups: renewable and nonrenewable. When a resource is used, it takes some time to replace it. If the resource can be replaced quickly, it is called renewable. For example, grass for animals is a renewable resource. When cows eat the grass, the resource is used. If the soil is fertilized and protected, more grass will grow. Coal, however, is nonrenewable because it takes millions of years to make coal. All fossil fuels are nonrenewable resources.

Solar energy, air, and water are renewable resources because there is unlimited supply. However, this definition may change if people are not careful with these resources. The amount of solar energy that reaches the earth depends on the atmosphere. If the atmosphere is polluted, the solar energy that reaches the earth may be dangerous. If life is going to continue, the air must contain the correct amount of nitrogen (N), oxygen (O), carbon dioxide (CO2), and other gases. If humans continue to pollute the air, it will not contain the correct amounts of these gases.