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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.
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