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As a SciShow viewer, you can  keep building your STEM skills for 20% off an annual premium  subscription at Brilliant.org/SciShow. [ intro ] If a tree falls in a forest and  doesn’t decompose, what happens to it? Well, like all living things on Earth,  trees are mostly made of carbon.

And, if that tree happened to  exist some 300 million years ago, that carbon might have turned into coal. In fact, we can thank ancient fallen forests for essentially the world’s entire supply of coal, the burning of which made  things like steam engines and the entire Industrial Revolution possible. Of course, it has also caused  some serious climate problems.

And while we look to uncover some of the  secrets of these coal-forming forests, we can also focus our efforts on getting  that carbon out of the atmosphere and back where it came from. Carbon is vital to all life on Earth. We find it everywhere, from  the bodies of living organisms, to the seawater and earth, and in  our atmosphere as carbon dioxide.

And it’s always moving through these forms through what’s called the carbon cycle. When an organism like a tree dies, it’s slowly broken down by decomposers, which are other organisms that are  specially adapted to eat dead stuff. Fungi are the dominant decomposers, but microorganisms and insects that  are adapted to chow down on dead stuff can also do a lot of heavy lifting.

Together they break down tissues and, over time, release the carbon in them  back into the atmosphere to be carbon dioxide gas again. But it turns out that’s not the  only fate of carbon in dead things. That carbon can also be taken out of this cycle and instead get stored in rocks and sediment.

Case in point: coal. Coal forms when carbon from  organic matter accumulates in layers that are compressed  over millennia into rock. And it turns out that the vast  majority of the world’s coal formed during a single geologic time period that started about 360 million years ago.

So much coal formed in this period that geologist literally named it after the amount  of carbon dating to this time, which is where we get the name Carboniferous.. Coal really piled up because  the trees and other plant life just flat out didn’t break down. And there’s never been a time since then where so much coal formed all  at once, in lots of different places.

So what gives? Let’s look back at  the Carboniferous Period to find out. Most of the world was pretty  tropical at that time.

Mild, humid environments were regularly flooded by the surrounding warm ocean waters,  and swamp forests reigned supreme. And these swamps saw the rise  of the first towering trees, but not the kinds of trees we’re used to today. They’re in a group of plants called lycopsids, and while today’s lycopsids are  only a few inches tall at most, their Carboniferous ancestors  grew upwards of 35 meters tall! .

These plants also contained a  fibrous tissue called lignin, which gives modern day  plants their rigid structure. Lignin is really tough—too tough, it turns out, for most decomposers to digest. Even today, there are only a  few fungi that have enzymes powerful enough to break it down.

So for a long time, scientists thought that fungi simply hadn’t yet evolved the ability to  break down the new woody fibers of plants yet. But in 2016, researchers instead proposed that tectonic plate movement was more  likely the influence of coal formation. They examined sediments from  this coal-forming period of time, and found that a lot of the  plant matter from this era still didn’t have all that much lignin!

And, there was a ton of  geologic activity at that time, moving around land masses that would  eventually combine into what we know as Pangea. This plate movement created tall  mountains and deep valley basins, which were the perfect places for  plant debris to accumulate en masse. The already humid environment was subject to regular flooding, causing the formation of thick marshy layers.

When you’re at the bottom of a waterlogged swamp, you won’t find much oxygen around. And one of the key ingredients  of decomposition is oxygen. So lignin or not, the fact that these swamps sealed out oxygen- protected the  plant matter from decomposing.

Given a few million years, all  that carbon compressed down to form the coal we know and burn today. We humans have been burning  coal for thousands of years. But coal really became important  during the Industrial Revolution, when we used it to power steam  engines and other technologies.

That made manufacturing easier, but it solidified our dependence on fossil fuels. And it’s now one of the biggest  contributors to our warming climate. All that coal was once a carbon sink.

For millions of years it kept the trapped  carbon locked away and out of the carbon cycle. By burning it, we’re adding much  more carbon into the atmosphere than would be there otherwise, all way faster than decomposers  ever could have done. So as we try to find solutions  to the climate crisis, we’re going to have to stop  burning so much carbon.

But, in thinking of other ways to mitigate the amount of carbon  in our atmosphere right now, we can also take some inspiration  from the Carboniferous period and start to sequester it too. Of course, we can’t rely on natural coal formation to happen at the scale it was  during the Carboniferous period. The conditions are too different today  from what was going on back then, not that it would even happen on  a timescale that will help us.

We just don’t have the millions of years to spare! But it turns out we have other ways  to get carbon back into the rocks where we got it from, geologically isolating  it and keeping it out of our atmosphere. Basically, we can inject it into  rocks in the form of carbon dioxide!

Rock types with certain minerals containing calcium, magnesium and iron are the  best candidates for this process, since those elements will react with  carbon dioxide to help lock it in place. It’s not exactly a straightforward solution, since these processes aren’t easy to pull off, and they can be very costly. Plus, there are potential risks.

Some studies have shown that chemical reactions within the rocks can cause the carbon dioxide  to find its way back into the atmosphere, and even into our drinking water. And not in a fun, fizzy water kind of way. Excess carbon dioxide in water systems can increase the amount of dissolved solids  in the water which affects the taste.

It can also make the water more acidic, and could even increase the metals present. Other research has even shown that if we pump that carbon  into the wrong locations, there’s a risk of triggering  earthquakes through this process, which is not ideal. So what locations are better  for geologic carbon storage?

Well, it’s looking like areas where  we’ve already extracted coal and oil are actually best suited to the process. See, when it comes to geologic  activity like earthquakes, areas that are chosen for mining tend  to be more quiescent, or dormant. So areas where we’ve extracted resources already may be better candidates for carbon  sequestration just because of that fact. .

So it does look like one day, large scale geologic carbon storage  could be one of the solutions we mobilize in an effort to gain control of  our massive climate change problem. Even if we have a long way to go before  we can store carbon deep in the rocks at the scale the ancient forests did, we can thank the Carboniferous  forests for two things: Giving us the high-octane fuel that  powered so many of our modern inventions, and inspiring the solutions that may allow  us to put that carbon back where we found it. You never know where you’ll find solutions to some of the world’s biggest problems.

And to help you discover those scientific  wonders in the world around you, there’s the Brilliant course,  “Physics of the Everyday.” Brilliant is an online  learning platform with courses in science, computer science, and math. Through interactive puzzles and lessons, they bring you into the world of STEM. This Brilliant course has an entire  section called “Fuel the World” that runs through the physics of fossil  fuels, solar power, nuclear energy, and more.

Then the next section takes that  knowledge out into nature to apply it. You’ll learn about the Greenhouse Effect and other environmental phenomena  related to those fuel systems. To get started, you can find the link in the description down below or  head to Brilliant.org/SciShow.

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