Oil is one of the most valuable resources on the planet because of our use of it in our cars, homes and a variety of other products. On average, we use over 19 million barrels of oil a day in the United States. With as much oil as we use every year, it’s important to understand the process of making it, so we can use it in a sustainable manner.
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Oil is defined as a fossil fuel that’s made from carbon and hydrogen. It takes a very long time and very specific circumstances for oil to form, and most of the oil that we use today started forming millions of years ago.
Roughly 10 percent of the oil that’s harvested today was formed during the Paleozoic age, which fell between 541 and 252 million years ago. Most of it formed during the Mesozoic era, which happened between 252 and 66 million years ago. The final 20 percent formed during the Cenozoic age, roughly 65 million years ago.
How is oil actually formed? It starts with ancient shallow oceans and the microscopic organic matter that called those oceans home — phytoplankton, zooplankton and algae in addition to the bacteria that thrived in those warm shallow waters. As the organisms died, they floated to the bottom of the ocean and mixed with the clay-like material that made up the river and ocean beds of the era.
This organic-rich mud envelops the dead organic matter, preventing it from decomposing. As millions of years pass, this mud layer is compressed and becomes sedimentary rock. The organic material becomes what is known as organic shale.
If the shale is deep enough, between one and 2.5 miles below the surface of the earth, it starts to get warmer and experience additional pressure. The pressure turns the organic shale into oil shale, also known as kerogen. This stage is where it gets a little bit tricky. At temperatures between 90 and 160 degrees Celsius, the kerogen turns into oil and natural gas. At any temperatures higher than 160, only natural gas or graphite is formed.
This temperature range is known as the oil window. Oil will escape from the oil shale and rise toward the water above, creating a reservoir. This situation is what prospectors are looking for when searching for new areas to drill — reservoirs that can be tapped into safely without damaging the environment.
If a prospector finds a sealed reservoir, they can drill into it and place pipes into the reservoir to draw the oil up to the surface where it can be transported to a refinery for processing. Earthquakes and other geological changes can bring these deposits closer to the surface, making it easier for us to access the oil.
While you might just think of oil as gasoline for your car, we use it in a variety of other products. Crude oil is a primary component in petrochemical feedstocks, which are used to make plastics. It’s also the main component in a number of different fuels, including kerosene, jet fuel and aviation gasoline.
It's even under your tires when you drive — petroleum is a primary component in the asphalt and road oil that’s used to create the roads and highways that crisscross the landscape.
If oil is constantly being formed by the heat and pressure of the earth's mantle, is there enough oil to last us forever?
The short answer is no. We're quickly using up all the accessible oil in the planet's crust, and it will take millions of years for more to form. As it stands, we'll probably run out of oil sometime in the next century, which means that it’s up to us to conserve the oil that we have left. Using less gasoline, which has a lower energy content than other types of fuel, such as heating oil, and also accounts for nearly half of our oil usage, is a good place to start.
As a species, we need to start using oil more responsibly. The planet might be making more of it, but our world isn’t getting any smaller.