Common Fuel Types and Uses | AP Environmental Science | Khan Academy

Not all fossil fuels are the same, and this is because different kinds of organic material were heated and compressed in different ways, creating different kinds of fossil fuels. One of these kinds of fossil fuels is petroleum. The word petroleum comes from the Latin word for rock, "petra," and the Latin word for oil, "oleum." This makes sense because it's an oily substance that's found in reservoirs trapped in rock.

Humans have been using oil for a very long time. Early civilizations found it bubbling up from the ground at natural wells. The oil they saw coming straight out of the earth is called crude oil or crude petroleum, which means that it is unrefined and unprocessed. Crude oil was probably one of the ingredients in Greek fire, which was a flame-throwing weapon that the Byzantines would fling at their enemies.

Today, we refined crude oil into many products like gasoline and diesel for vehicles, kerosene for heating, and asphalt for road construction. It's also used to make plastics and synthetic fabrics. Another type of fossil fuel is coal, which we mostly burn to make electricity, but it can also be used for heating and cooking. It's a solid, shiny black flammable rock, which is mostly formed from the carbon remains of fossilized plants like moss.

Over thousands of years, plant material transforms into a carbon-rich compound called peat. Then, with some pressure, it becomes soft coal, which is called lignite. With more pressure, it becomes bituminous coal, and then finally, it becomes a hard coal called anthracite. The longer the plant remains are put under pressure, the more energy-dense it becomes. So, if you burned anthracite, you would get a lot more energy than if you burned peat.

Burning coal releases carbon dioxide, sulfur dioxide, nitrogen oxides, and other gases into the air, so coal is one of the dirtiest fossil fuels. The cleanest burning fossil fuel is natural gas, meaning that it emits the least amount of carbon dioxide or other air plumes. This is not the same type of gas as we put into our vehicles; that type comes from petroleum. Instead, natural gas is mostly used for generating electricity, heating homes, and cooking food. Your oven, furnace, water heater, dryer, or grill all might run on natural gas.

Natural gas is a naturally occurring mixture of gases, and it's mostly made up of methane, ethane, propane, and butane. The gas is colorless and odorless, so natural gas companies often add a rotten egg smell to the fuel to make leaks easier to detect. But, even though we can't see or smell natural gas, humans have been detecting it and using it for centuries. There is evidence that more than 2,000 years ago, people in China created bamboo pipelines to transport the gas so that they could use it to boil salt water and separate out the salt. Today, we still use pipelines to transport gas across land, although they're no longer made out of bamboo.

Another kind of non-renewable resource is nuclear fuel. Nuclear power plants don't burn fossil fuels; instead, they split uranium through something called nuclear fission. Just one kilogram of uranium can produce 24 million kilowatt-hours of energy. Compare that with one kilogram of coal, which can produce eight kilowatt-hours of energy. In other words, nuclear fission produces a lot of energy.

It also produces a lot of heat, which we mostly use to make electricity. Also, nuclear energy is known as clean energy because the only greenhouse gas emission is water vapor, which tends to cycle out of the atmosphere faster than other greenhouse gases. But the downside is that the spent fuel is a dangerous radioactive waste, and recycling the nuclear waste is dangerous and expensive.

Petroleum, coal, natural gas, and nuclear fuel make up 85 percent of the world's energy consumption. But as our populations and energy needs grow, it's becoming more important to integrate renewable resources—sources that could be restored by natural processes—into our energy mix.

Here's something to think about: What's something that you do in your day that uses energy? Does that energy come from fossil fuels, and if so, which one? Understanding how you get your energy is part of understanding what powers your community, your country, and the world.