As the world population grows , people are becoming more concerned about the impact of human activity upon the earth . Things that are used by humans are called resources . There are two types of resources ; renewable and finite . Finite resources are those which are limited in amount ; no more can be made and when all of it is used , there will be no more of it . Usually , as finite resources are used up , they become more expensive . Examples of finite resources are land , petroleum products , and ores . Renewable resources are those which replace themselves or can be replaced regularly . Examples of renewable resources are trees , food , wind , grass , solar , and items which are recycled . The cow is a great example of a renewable resource which provides a wide variety of benefits to humans , environmentally , nutritionally , and economically .