Oil seems to pop up everywhere, in shale under deserts and plains, and of course, under water. But if oil is a fossil fuel, how do those fossils get under the ocean? Music. Hey slick, Trace here for DNews. Oil is a mystery. Scientists don't really know where it came from or how it got underground. But because we know about plate tectonics, we 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 actually more or less random. Roger and 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, and swamps. Think of it this way: the ocean is deep, and when things die at the top, they 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, that's for plants). 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 quickly and find its way to a place without oxygen to avoid regular decomposition. Oceans are great for this because the seafloor is not very oxygenated. At that point, it breaks down super slowly, and more...