But if oil is a "fossil" fuel, how did those fossils get under the ocean?

Hey slick, Trace here for DNews.

Oil is a mystery.

Scientists don't really 100 percent know where it came from or how it got underground, but

because we know about plate tectonics we at least have some ideas of how it got under

the ocean.

Oil is what we call a fossil fuel.

It comes from dead things, especially when there are a lot of them gathered in one place.

It's true that oil famously comes from deserts like on the Arabian peninsula, but that location

is, well, more-or-less random.

Roger N. Anderson of Columbia University told Scientific American, "Plate tectonics determines

the location of oil… reservoirs."

Because the Earth's surface is constantly changing and shifting, oil can end up in all

sorts of weird places…

It helps to understand how oil is made first though.

Hundreds of millions of years ago, organic material (prehistoric plants and animals)

accumulated at the bottom of oceans, rivers, swamps.

Think of it this way, the ocean is deep, and when things die at the top, they can sink

all the way to the bottom.

When that happens a lot, they'll pile up!

Living things are made of proteins, carbohydrates, lipids (or fats) and lignin (woody polymers).

When these decomposing organics become compressed under more and more material, in an anoxic

environment, they break down strangely.

Essentially, the organic matter had to die and quickly find it's way to a place without

oxygen to avoid decomposition.

Oceans are great for this because the seafloor is not very oxygenated.

At that point it breaks down SUPER slowly, so more and more dead stuff can build up and

adds more and more pressure.

Eventually, the pressure of all that material forces the water out; the proteins, lignin

and carbs break down; and all that is left is a lipid, sugar, and amino acid ooze.

Occasionally, this happens near enough to a crack in the crust that it can become trapped.

Then, by adding heat and pressure (something geology and plate tectonics is great at),

this mix of decomposed organisms become subject to chemical reactions, forming what's called

kerogens.

Over millions of years and with more heat and pressure it goes through catagenesis where

the kerogen cooks into hydrocarbon chains.

Humans then look for telltale signs of the these deposits.

When that happens though, it doesn't form a giant lake or pool under the ground; it's

actually stuck in the pores of surrounding rocks, like water clinging to a windowpane.

The immense pressure of the Earth's crust can keep the oil trapped under solid rock,

but if an oil well pushes through it at the right place -- the oil can gush out in a tower

of black liquid.

Companies can then take this and make petroleum!

(WHEW)!

The more we understand about where ancient seas and forests were, the better scientists

can predict where oil is trapped in Earth's crust today.

So, because oceans are great at providing the perfect conditions of low oxygen and high

pressure, AND it's where a lot of this decomposing organic animal and plant matter accumulates…

oil could be anywhere there used to be an ocean.

As the Earth's crust is constantly shifting, the locations of these ancient oceans have

moved too -- scattering oil across the planet; 70-percent of which is covered by water -- so

there's likely a lot of oil trapped under there!

Getting at that oil isn't easy though.

Deepwater Horizon -- could reach 10,000 feet to the ocean's floor, and then drill over

30,000 more feet into the rock to extract the oil.

The tallest building in the world, the Burj Khalifa, is only 2717 feet.

In the end, we think oil got down there because the Earth is constantly changing.

What was once under the ocean is now on top of Mt Everest -- they have undersea fossils

that they found there.

And what was once on top of the world, is now at the bottom of the sea.

How poetic.

We'd like to thank our sponsor for this episode for helping support DNews today: Deepwater

Horizon, the movie.

Check out Deepwater Horizon, based on a true story.

In theaters September 30th.

After learning all about oil, maybe you're curious about how we take uranium and we turn

that into nuclear fuel as well?

Luckily, we have a great video on that

right here.

Are there other processes you want to know about?

Should we look into how oil is refined?

What do you want to know about the world around you?