A natural resource is any material that exists naturally and has economic value, such as trees, water, soil, air, and minerals. Resources are either renewable, like trees and solar energy which can regenerate within years, or nonrenewable, like soil, fossil fuels, and minerals which take extremely long periods to form. Because nonrenewable resources can easily run out, conservation of resources like soil, air, water, and fuels is important through practices such as preventing erosion, reducing pollution and waste, and using renewable energy whenever possible.