How Did So Much Oil Get Trapped Under The Ocean?

What is oil even made of? Here's how fossil fuels form in the ocean and how scientists know where to find it.

Just as there is a lot of oil beneath dry land -- well, not as much as there used to be -- there's also a lot of oil under the oceans. But if oil comes from dead dinosaurs, how did it get under the sea?

Funny you should ask. Trace Dominguez digs deep in today's edition of DNews.

First things first: Oil isn't really dead dinosaurs. At least, it's not entirely dead dinosaurs. Petroleum as we know it is the end result of an enormously long and complex process that begins with the decomposition of several different organic materials: plants, fish, animals -- and, yes, the occasional pterodactyl.

The ocean floor is actually a perfect place for oil to form, over the course of millions of years. Most things that die in the ocean eventually sink to the bottom. Many things that die on land get swept by rain into rivers and eventually wind up in the ocean. And the bottom of the ocean doesn't have much oxygen, which is a good thing when you're trying to turn organic matter into high-energy slop.

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Living things are made of proteins, carbohydrates, lipids (or fats) and lignin (or woody polymers). When these decomposing organics become compressed -- in an anoxic environment -- they break down strangely. Add heat, pressure and several million years, and the slop undergoes chemical processes that produce hydrocarbon chains. These eventually become petroleum or natural gas, depending.

The interesting twist is this: The petroleum deposits that exist now -- the places we drill for the stuff -- are where oceans used to be, and not necessarily where the oceans are today. That's why we find oil in unlikely places like the Arabian Peninsula, or Texas. Of course, because 70 percent of the Earth's surface is covered in water, plenty of deposits are still beneath our existing oceans.

We just have to go waaaay down to it. An offshore drilling rig like Deepwater Horizon can reach 10,000 feet to the ocean's floor -- then drill over 30,000 more feet into the rock to extract the oil. Consider that the tallest building in the world, the Burj Khalifa, is only 2,717 feet. Wild.

-- Glenn McDonald

Learn More:

Live Science: The Mysterious Origin And Supply Of Oil

Scientific American: Why Is Oil Usually Found In Deserts And Arctic Areas?

Stanford University: Stanford Scientists Discover How Pangea Helped Make Coal