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The Critical Angle: Does our oil really come from dead dinosaurs?
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The Critical Angle: Does our oil really come from dead dinosaurs?

Who doesn’t want a Triceratops in their tank?

Every February, to help celebrate Darwin Day, the Science section of AIPT cranks up the critical thinking for SKEPTICISM MONTH! Skepticism is an approach to evaluating claims that emphasizes evidence and applies the tools of science. Every day this month we’ll be highlighting skepticism in pop culture and skepticism of pop culture.

Today paleontologist Jim Lehane takes a closer look at a common assertion that’s also the premise of the upcoming comic, Tankers: did the bodies of decomposing dinosaurs become the oil we extract from the Earth today?

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Tankers follows the story of an oil company worried about losing their reserves in the coming years, as the natural supply starts to run out. Their estimate is that within about 50 years, our oil reserves will be exhausted. The actual numbers for this aren’t exactly known, for several reasons — ever-evolving technology, more reliance on “unconventional” oil sources (such as tar sands and fracking), the transition away from oil toward more renewable resources like solar and wind energy, and a growing global population demanding ever more resources. Regardless of the length of time that oil reserves will last, scientists generally agree we’re nearing the “peak” of our supply, meaning we’ll soon be on the downward trend of available oil.

With this in mind, the protagonists of Tankers determine they need to make more oil. To do this they need to increase the source material, which in their interpretation is the decaying bodies of dinosaurs (oil is a fossil fuel, after all). By going back in time and redirecting the asteroid that hastened their extinction, they can allow dinosaurs to live for another 50 million years, providing loads more organic matter to produce petroleum.

It’s a deliberately absurd premise, for obvious reasons and another that might not be so apparent. Oil does come from decaying organic matter, but it’s not from dinosaurs.

The Critical Angle: Does our oil really come from dead dinosaurs?

That’s one way to make a fossil.

Let’s break this down a little bit. All of our oil-containing rocks come from the Phanerozoic Eon (the last ~541 million years of the planet, during when the majority of life has existed). The Phanerozoic is broken down into three eras. The Paleozoic (514 to 251 million years ago) is the time when life exploded onto the planet; 10% of our oil reserves come from rocks of this age. The Mesozoic (251 to 66 million years ago) is the age of the dinosaurs, and 70% of oil reserves come from this time. The most recent era is the Cenozoic (66 million years ago to today), which is known as the age of mammals. The final 20% of oil reserves come from this time.

Despite 70% of our oil coming from the “age of dinosaurs,” dinosaurs themselves only make up a very, very small portion of all the life that’s ever existed on Earth, from a pure mass standpoint. A recent evaluation of the current biomass across all kingdoms of life determined that a whopping 81.8% of all of it is plants. Another 12.7% is bacteria, leaving only 5.5% of the biomass left for non-photosynthetic organisms. Animals only equate to less than one half of one percent of the world’s entire biomass.

Looking at those numbers, it should be no surprise that most oil actually comes from dead plankton, including phytoplankton, zooplankton, algae, and bacteria. As these tiny organisms die, they sink to the bottom of the oceans, where they get mixed up with the mud and sediment already on the bottom, and new sediment is actively deposited on top of them. One of the key ingredients into turning this dead soup into oil is lack of oxygen (this type of environment is known as an anoxic environment). Oxygen allows for other organisms, as well as chemical reactions, to break down the organic matter over time. Without oxygen, the organic matter can’t break down, and it stays around.

Over time this mud/dead life slurry is buried by more mud and dead life. The slurry is eventually compacted, hardening into the rock called shale. With increased pressure comes increased temperature, and as the lower layers start to heat up, they essentially “cook” the organic matter, creating a waxy, organic-rich material called kerogen. As the temperatures of the rocks increase, the kerogen transforms into other organic materials, like oil (at temperatures between 90° and 160°C) and natural gas (at temperatures greater than 160°C).

dinosaur oil plastic

This meme lied to me.

So is it just a coincidence that most of our oil comes from the age of dinosaurs? Not exactly. For much of the Mesozoic Era, the Earth was much warmer than it is now, creating ideal conditions for life across the globe to proliferate. This increased abundance of life led to an increase abundance of dead life, specifically bacteria, algae, and other planktonic organisms, that was later cooked and converted to oil. Similar conditions (warm and wet) also existed during the period of the Paleozoic Era known as, unsurprisingly, the Carboniferous.

Editor’s note: Of course, that’s all if you discount the abiotic hypothesis of oil production, which claims it’s made (somehow) by carbon monoxide and hydrogen gases rising from deep within the Earth. But that’s a whole different kind of absurdity. 😉

The Critical Angle is a recurring feature that uses critical thinking and skepticism to analyze pop culture phenomena. Skepticism is an approach to evaluating claims that emphasizes evidence and applies the tools of science. Rather than repeating the same old arguments, we put them to the test.

AIPT Science is co-presented by AIPT and the New York City Skeptics.

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