The natural environment includes all natural resources that are necessary for life: the air. the oceans, 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 caretully.

According to ecologists, resources are divided into 2 groups: renewable and non-renewable. When a resource can be replaced quickly, it is called renewable. If it cannot be replaced quickly and easily, it is non 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 nonrenevvable resources.