Natural resources are natural substances required by humans for different needs. They include metals, minerals, water, crops, forests, and rainforests. Natural resources such as oil, gas, coal, wood, wind, sunlight and waves can be used to produce energy and are called energy resources. Non-renewable energy sources like oil, natural gas and coal cannot be easily replaced as they take millions of years to form, whereas renewable resources such as wind power, solar power, and hydropower can be replaced and will not run out.