We can classify natural resources as either renewable or nonrenewable. Coal, oil, and gas are nonrenewable. They take millions of years to form. Some scientists predict that we will run out of and gas in 50 to 100 years. Coal is more plentiful. So it may last for hundreds of years. Resource as wood and water are renewable. They can be grown or recycled naturally. They can, however, become limited from overuse.