Energy and power are closely related but aren't an equivalent physical quantity. Energy is that the ability to cause change; power is that the rate energy is moved, or used. Energy is important to life and every one living organisms. The sun, directly or indirectly, is that the source of all the energy available on Earth. Our energy choices and decisions impact Earth's natural systems in ways we might not remember of, so it's essential that we elect our energy sources carefully. The energy sector or industry includes companies involved within the exploration and development of oil or gas reserves, oil and gas drilling, and refining. The energy industries also comprise integrated power utility companies like renewable energy and coal. Divided energy uses among four economic sectors: residential, commercial, transportation, and industrial. Heating and cooling our homes, lighting office buildings, driving cars and moving freight, and manufacturing the products we believe in our daily lives are all functions that need energy.