Fossil fuel formation: Key to atmosphere's oxygen?

Fossil fuel formation: Key to atmosphere’s oxygen?
This black shale, formed 450 million years ago, contains fossils of trilobites and other organic material that helped support increases in oxygen in the atmosphere. Credit: University of Wisconsin-Madison

For the development of animals, nothing—with the exception of DNA—may be more important than oxygen in the atmosphere.

Oxygen enables the chemical reactions that animals use to get energy from stored carbohydrates—from food. So it may be no coincidence that animals appeared and evolved during the "Cambrian explosion," which coincided with a spike in roughly 500 million years ago.

It was during the Cambrian explosion that most of the current animal designs appeared.

In green plants, photosynthesis separates into (which is released to the atmosphere), and (which is stored in carbohydrates).

But photosynthesis had already been around for at least 2.5 billion years. So what accounted for the sudden spike in oxygen during the Cambrian?

A study now online in the February issue of Earth and Planetary Science Letters links the rise in oxygen to a rapid increase in the burial of sediment containing large amounts of carbon-rich organic matter. The key, says study co-author Shanan Peters, a professor of geoscience at the University of Wisconsin–Madison, is to recognize that sediment storage blocks the oxidation of carbon.

Without burial, this oxidation reaction causes dead plant material on Earth's surface to burn. That causes the carbon it contains, which originated in the atmosphere, to bond with oxygen to form carbon dioxide. And for oxygen to build up in our atmosphere, plant organic matter must be protected from oxidation.

And that's exactly what happens when organic matter—the raw material of coal, oil and natural gas—is buried through geologic processes.

To make this case, Peters and his postdoctoral fellow Jon Husson mined a unique data set called Macrostrat, an accumulation of geologic information on North America whose construction Peters has masterminded for 10 years.

The parallel graphs of oxygen in the atmosphere and sediment burial, based on the formation of sedimentary rock, indicate a relationship between oxygen and sediment. Both graphs show a smaller peak at 2.3 billion years ago and a larger one about 500 million years ago.

"It's a correlation, but our argument is that there are mechanistic connections between geology and the history of atmospheric oxygen," Husson says. "When you store sediment, it contains that was formed by photosynthesis, which converted carbon dioxide into biomass and released oxygen into the atmosphere. Burial removes the carbon from Earth's surface, preventing it from bonding molecular oxygen pulled from the atmosphere."

Some of the surges in sediment burial that Husson and Peters identified coincided with the formation of vast fields of fossil fuel that are still mined today, including the oil-rich Permian Basin in Texas and the Pennsylvania coal fields of Appalachia.

"Burying the sediments that became was the key to advanced animal life on Earth," Peters says, noting that multicellular life is largely a creation of the Cambrian.

Today, burning billions of tons of stored carbon in fossil fuels is removing large amounts of oxygen from the atmosphere, reversing the pattern that drove the rise in oxygen. And so the in the atmosphere falls as the concentration of carbon dioxide rises.

The data about North America in Macrostrat reflects the work of thousands of geoscientists over more than a century. The current study only concerns North America, since comprehensive databases concerning the other 80 percent of Earth's continental surface do not yet exist.

The ultimate geological cause for the accelerated sediment storage that promoted the two surges in oxygen remains murky. "There are many ideas to explain the different phases of ," Husson concedes. "We suspect that deep-rooted changes in the movement of tectonic plates or conduction of heat or circulation in the mantle may be in play, but we don't have an explanation at this point."

Holding a chunk of trilobite-studded Ordovician shale that formed approximately 450 million years ago, Peters asks, "Why is there oxygen in the atmosphere? The high school explanation is 'photosynthesis.' But we've known for a long time, going all the way back to Wisconsin geologist (and University of Wisconsin president) Thomas Chrowder Chamberlin, that building up oxygen requires the formation of rocks like this black shale, which can be rich enough in carbon to actually burn. The organic carbon in this shale was fixed from the atmosphere by photosynthesis, and its burial and preservation in this rock liberated molecular oxygen."

What's new in the current study, Husson says, is the ability to document this relationship in a broad database that covers 20 percent of Earth's land surface.

Continual burial of carbon is needed to keep the atmosphere pumped up with oxygen. Many pathways on Earth's surface, Husson notes, like oxidation of iron—rust—consume free oxygen. "The secret to having in the atmosphere is to remove a tiny portion of the present biomass and sequester it in sedimentary deposits. That's what happened when fossil fuels were deposited."


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Citation: Fossil fuel formation: Key to atmosphere's oxygen? (2017, January 2) retrieved 23 October 2019 from https://phys.org/news/2017-01-fossil-fuel-formation-key-atmosphere.html
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Jan 02, 2017
Sounds like the simple solution is - more plants...

Jan 02, 2017
Sounds like we need to sequester the carbon, not release it from stores. Unfortunately we need to implement alternative energy sources before we can reverse this current destruction caused by burning of fossil fuels.

Jan 03, 2017
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Jan 03, 2017
. Unfortunately we need to implement alternative energy sources before we can reverse this current destruction caused by burning of fossil fuels.

What's unfortunate about that? If ever there was a business opportunity then this is it. It's win-win for everybody (except those clinging to old paradigms, of course)

Jan 03, 2017
If ever there was a business opportunity then this is it.


That depends on whether people are willing to pay for it. Sequestering carbon is literally sinking resources in the ground, and it costs resources to do so, which means a society that does that has to lower its living standards or increase resource production to pay the difference.

The latter of course doesn't make very much sense, because in our immediately foreseeable future it would simply mean burning up more carbon to come up with so much extra energy.

The former is simply a question of how many poor people you're willing to throw under the bus - because they're hit by the austerity first - and how that affects your standing as a political leaders.

Perhaps in the far future, 50-100 years from now when the renewables have actually caught up to speed, we can start using the surplus to sequester carbon on the large scale.

Jan 03, 2017
Now, here's the trick to the above: do you mean sequestering Carbon, or CO2?

There's a subtle difference, because the article is talking about sequestering carbon and liberating oxygen, which means reversing the combustion of CO2 back to C and O2 and that requires a ton of energy. That wouldn't be doable with our current means, except on a tiny scale that wouldn't matter.

If you simply sequester CO2 into minerals, that takes far less. You just lose the oxygen.

Jan 03, 2017
Sounds like the simple solution is - more plants...

Shhh... millions can't be made from the obvious and best solution.

Jan 03, 2017
50-100 years = "far future"? That is the present, geologic time. Only tomorrow, Human time. Only the far future in mayfly years..... If we let our attention be drawn away by the "renewables aren't ready" misinformation and not use the next 50 years wisely, there will be no "far future" for Humans.

Jan 04, 2017
Sounds like the simple solution is - more plants...

Shhh... millions can't be made from the obvious and best solution.


Shhh... But Trillions can be made and is being made as we speak by letting the oil cartel destroy our earth, through greed, corruption and disrespect to humankind.

Jan 07, 2017
50-100 years = "far future"? That is the present, geologic time.


Humanity can barely see 10 years in the future. We can make plans for about 15 years into the future, but beyond that it starts to break down because we can't ensure our own social and economic stability.

And, remember what the year 2000 was supposed to be like, back in the 70s?

If we let our attention be drawn away by the "renewables aren't ready" misinformation and not use the next 50 years wisely


We don't have 50 years. We have about 10 years before the current energy systems start to grow too old and nuclear power starts to drop offline, at which point we'll be losing 20% of the electricity generation worldwide and the renewables just can't keep up with that.

Jan 07, 2017
Fossil fuel burning, key to atmosphere's CO2, plant and all animal life on the planet.

Jan 07, 2017
This is assuming that 'fossil fuels' arent abiogenic. But as hydrocarbons can be found throughout the solar system, why wouldnt we expect to find them here as well? Or for that matter, on the moon and mars?

Jan 07, 2017
This is assuming that 'fossil fuels' arent abiogenic. But as hydrocarbons can be found throughout the solar system, why wouldnt we expect to find them here as well? Or for that matter, on the moon and mars?

You wouldn't expect to find large pools and high concentrations of abiogenic long chain hydrocarbons like oil unless the whole place was swimming in simpler hydrocarbons like methane and there was some funky chemistry going on.

Life is basically a catalytic reaction.

The soviets were big on the abiogenic petroleum theory, but they failed to produce any useful results - ie. oil wasn't found where the theory would predict. Meanwhile oil -was- found where the biogenic theory predicted.

Jan 07, 2017
You wouldn't expect to find large pools and high concentrations of abiogenic long chain hydrocarbons like oil unless the whole place was swimming in simpler hydrocarbons like methane and there was some funky chemistry going on
"Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes..."

"oil and natural gas are often found together. In common usage, deposits rich in oil are known as oil fields, and deposits rich in natural gas are called natural gas fields..."

-next question?
oil wasn't found where the theory would predict. Meanwhile oil -was- found where the biogenic theory predicted
-And what if we strike 'oil' on mars? Then we would need to figure out why abiogenic hydrocarbons arent found here on earth. Or reinvestigate the stuff that already is.

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