Did you know that just the coal reserves in the U.S. can produce more energy than all the recoverable oil left in the world? The other “black gold” is an object of plenty of controversy, and an extremely potent source of energy. Let’s take a closer look.

Where does coal come from?

Like petroleum and natural gas, coal is a fossil fuel. And like all fossil fuels, it’s organic material that has been mixed with acidic water, covered with layers of rock, and left to “cook” for hundreds of millions of years.

To take a step back and see how that process plays out for coal, we should start in the swampland that thrived during the Carboniferous Period. Here, deep, dense layers of plants died, creating a feast for hungry bacteria. The bacteria consumed oxygen along with the plant matter, depleting the swamp of its oxygen supply so that plants no longer decayed. And that’s how we got peat.

For the peat to turn into coal, it was covered by layers of sediment (rock) and pressed into the earth’s hot core. Over time, as it compressed and warmed up, the peat became denser and more potent, eventually transforming into coal.

Coal that formed during the Carboniferous Period is the oldest you’ll find on the continent, and it’s mostly clustered around Appalachia. Younger coal deposits in North America can be found further west. The older a coal deposit is, the more energy it will produce.

How does it create energy?

We turn coal into electricity the same way the earth turned peat into coal: By burning it. Here’s the whole process:

First, we crush coal into a fine powder, then mix the powder with hot air.

The combination is moved to a furnace, where it heats water in a boiler to create steam. (This is where the heat energy transforms into mechanical energy.)

The steam powers a turbine engine, which powers a generator (transforming the mechanical energy into electricity).

Finally, the steam cools down and returns to the boiler, and the process begins again with more coal.

What’s the environmental cost of Coal?

The use of coal as an energy source impacts the environment in two ways: The waste we produce by burning it and the effect of mining on our landscape.

Since coal is composed mainly of carbon (like every fossil fuel), it generates carbon dioxide when we burn it to produce electricity. Carbon dioxide emissions are responsible for the greenhouse effect in the atmosphere, the phenomenon which causes global warming. Along with carbon dioxide, burning coal creates toxins like mercury, lead, arsenic, and residue like “fly ash” that, if not contained, can have disastrous effects on public health. There’s also concern about sulfur dioxide emissions, which are related to acid rain. Luckily, cleaner coal solutions like integrated gasification combined cycle (IGCC) and carbon sequestration can reduce these dangerous emissions. So, while coal is not clean or renewable, we can reduce its harm.

The damage from mining is harder to keep in check – especially surface mining, which involves removing mountaintops. This damages ecosystems and alters the natural landscape.

What are its common uses?

93 percent of coal we use in the U.S., we’re using to generate electricity. Because of its environmental impact, we’ve been reducing our use of coal in the U.S. over the past couple of decades. But it still accounts for about 30 percent of our country’s electricity production, usually from power plants. Other uses of coal include steel production and cement manufacturing.

How much does coal cost?

Conventional wisdom dictates that coal is the cheapest fossil fuel. It’s readily available and requires very little processing before we can turn it into electricity. Plus, in most places, the infrastructure is already in place. And the data agrees. Compared with oil and natural gas, coal is the cheapest source of nonrenewable energy. However, as public opinion changes and we burn through our supplies, the cost of coal is rising. Economists expect coal to continue getting more expensive through the year 2040.