Nearly all other sources of energy originally got their energy from the sun. Organic matter, like plants, convert solar energy into leaves, flowers and fruits. Animals, which eat organic matter, convert the energy into body mass. When animals die, their energy is decomposed and over extensive time, becomes stored as oil, coal or natural gas. Hold up an apple, orange or other fruit or vegetable.
Food is the source of energy used by people.
Food that we eat is digested, and the stored energy is used by the body to keep the heart beating, the blood pumping and the body growing. Hold up a bottle of vegetable oil. Vegetable oil and animal oil have played an important role in human history. Vegetable oils, like olive oil, corn oil or safflower oil, are often used in cooking. Animal oil, like that from whales, seals and livestock, was used in the past for lighting lamps as well as for waterproofing.