Climate change, at least, the current climate change is all
about the carbon. Human society is emitting large amounts of fossil carbon into
the atmosphere at rates much faster than typically seen in the geologic record.
We call it fossil carbon because this carbon is coming out of the rock
reservoir, its carbon that hasn’t been in play in the fast carbon cycle up here
on the surface for hundreds of millions of years. What we are experiencing is a
major flux of carbon out of long term storage, which is then having a major
impact on the atmosphere, oceans and climate system, pretty much everything
here on the thin surface of the Earth on which we live. Another name for this
flux of carbon is called the industrial revolution, and the industrial
revolution was fueled initially by coal, so that is where we will start today’s
discussion.
The fast carbon cycle, as it pertains to coal, consists of
plants drawing carbon dioxide out of the atmosphere. Plants take carbon dioxide
gas and water and use the energy of the sun to break up those molecules and
reform them into a higher energy molecule, glucose. The energy from the sun is
then effectively stored as this higher energy molecule. The glucose molecule
can then be used for energy for the plant to form other structural or
physiological molecules like protiens or fats, or can be directly converted
into long chain carbohydrates. When the plant dies, or is eaten, organisms that
include animals, fungus and bacteria break down all those higher energy
molecules, and use the energy of the sun stored within to do their own
physiologic bidding. As part of that deconstruction process, the molecules are
converted back into carbon dioxide and water and released. That’s the basic
fast carbon cycle, plants take it in, and decay lets it out.
The Industrial Revolution really began some 325 million
years ago, give or take, when some interesting things began to happen on Earth,
and the carbon that we are dealing with today started getting taken out of the
atmosphere. This geologic era is known as the Carboniferous, because of what
happened to atmospheric carbon, and the average carbon dioxide level during
that time, which stretched from 354 to 299 million years ago, was 800 ppm. For
reference, we started the Industrial Revolution at 280 ppm and we have steadily
increased to our current 400 ppm, with no stopping in sight. It was generally
warmer, but keep in mind, we are talking about a 50 million year time period,
with all kinds of tectonic activity, so there was certainly climatic variation.
Biologically, it was very different than today. Virtually none of the animals
we know today existed. Plants had made the transition from water to land, but
there were no flowering plants, they hadn’t evolved yet. All terrestrial plants
were things like ferns and club mosses the size of trees. The fact that this
was still quite early in Earth’s evolutionary history is an important fact to
keep in mind as the story continues.
Conditions on Earth favored rapid growth of these tree ferns
and tree sized club mosses, in tropical swamps that formed along the edges of
the continents that now make up the Northern Hemisphere. Sea level changed
repeatedly, so these swamps were repeatedly inundated with sea water, when the
sea water receded, the brackish swamps continued to grow. The organic matter
from these giant fern swamps built up fairly rapidly, which is a little
unusual. Think back to the basic carbon cycle, plants take carbon in, and decay
mediated by animals, fungi and bacteria releases carbon back out. In this case
decay wasn’t happening , and each time the swamp was covered by the ocean,
another layer of undecayed organic material was buried under sediment.
Scientists think the reason that this swamp forest material didn’t break down
was because the plants had recently evolved a substance called lignin. Lignin
is a common substance today, found in wood everywhere, but at the time it was a
pretty new invention. And likewise, today, lignin is broken down by white rot
fungi. But because in the Carboniferous lignin was so new, nothing had evolved
to break it down and decay it. Because nothing
could decay it, it built up in thick layers. So all the carbon that the giant
ferns and club mosses pulled out of the atmosphere and incorporated into their
bodies in the Carboniferous period got buried under sediment and over a
hundreds of thousands of year period, was slowly transformed into coal.
All that carbon moved out of the atmosphere 300 million
years ago, and stayed out, buried in the ground. We discovered it and realized
we could burn it, and use the heat to heat water to make steam to do work, and
change the world. Really, we are just returning the carbon to the atmosphere
that was there in the Carboniferous. But the world was very different in the Carboniferous,
there were barely mammals, let alone humans. I don’t think I want to live in
the Carboniferous, but if we put all that stored away carbon back where it came
from, that is just where we are heading.
References:
University of California Museum of Paleontology strikes
again : http://www.ucmp.berkeley.edu/carboniferous/carboniferous.php
Fun stuff from the BBC, including videos from Wales: http://www.bbc.co.uk/nature/ancient_earth/Coal_forest#intro
Fungus (or lack thereof) may have been the key to coal
formation: http://www.scientificamerican.com/article/mushroom-evolution-breaks-down-lignin-slows-coal-formation/
Time line of coal in industrial society from the American
Museum of Natural History: http://www.amnh.org/exhibitions/past-exhibitions/climate-change/how-did-we-get-here/the-rock-that-burns
Info on the rise of atmospheric CO2: http://earthobservatory.nasa.gov/Features/CarbonCycle/page4.php
We may be getting
ahead of ourselves here but this solutions site looks pretty good: http://www.thinkglobalgreen.org/carbondioxide.html
