Wednesday, June 11, 2014
Climate Change Part 10: The Carboniferous Period
Note: This program first aired June 7, 2014.
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.
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