Chemistry, CO2, and the Anthropocene

This is a creative project that I wrote for my general chemistry class.
I find the scientific connections between chemistry, geology, and climate change extremely interesting, and my goal in this project was explaining it in a way that many people could understand.
Hope I accomplished that at least somewhat.
- Bianca

Chemistry, CO_2, and the Anthropocene: Understanding Humans Chemical Effect on the Climate

We are currently in an ice age. 

Some geologists call our time the Quaternary Period, but some people call it the Anthropocene.

Every 20,000 years, our ice age cycles between the earth being covered by 10% ice and being covered by 30% ice. Our earth has been cycling this way for the last 2 million years, between 30% and 10% ice coverage, and has completed this cycle around 20 times…

Source: https://www.ncdc.noaa.gov/abrupt-climate-change/Glacial-Interglacial%20Cycles

During the Mesozoic Era, 252.2 to 66 million years ago, there were two of earth’s biggest mass extinctions to begin the Era and to end it. During the Mesozoic, the earth was really, really hot, with CO₂ levels at about 4000 ppm (parts per million), meaning that “greenhouse gases” were at a high. 

Source: https://www.britannica.com/science/evolution-scientific-theory

The extinction event at the end of the Mesozoic killed about 75% of all plant and animal species on earth. Almost none of the earth was covered by ice, and much of the land on earth was covered by water, since there were low levels of sea ice.

But now we are in the Anthropocene epoch. Anthropo- means human: it’s the epoch that humans have been shaking things up for. Some scientists suggest that this epoch should be considered to have started around 12,000-15,000 years ago when human societies started farming on a larger scale. This is also called the “Neolithic Revolution.”

The Neolithic revolution is also when some scientists think that humans may have started affecting the amount of greenhouse gases (like CO₂ ) that are in the atmosphere.

Remember the 20,000 year cycles of ice? Well, we are theoretically in the middle of one of those cycles, meaning that the Neolithic Revolution would have been at the beginning of our current 10% ice coverage status within our ice age.

We know about increased amount of farming during the Neolithic Revolution because of a chemical process scientists use called “carbon dating.”

Carbon has multiple “isotopes,” which are versions of the same element (Carbon for example) that have the same number of protons, but different numbers of neutrons, the neutral particles in the nucleus, or middle, of an atom. Different isotopes of atoms are more or less “stable.”

So, for example, Carbon 14 (¹⁴₆C) is too large to be stable, and the ratio of protons to neutrons is uneven, making Carbon “decay” – it spits out a neutron, keeps a proton, and spits out a nuclear electron.

¹⁴₆C  à  ₁₄N + B^- (Beta particle, or radiation)

Therefore Carbon 14 has a “Half-life,” or a time for half of those radioactive elements to decay.

There’s a lot of Carbon in decaying organic matter: "organic matter" that humans were farming about 12-15 thousand years ago. So, scientists measure the radiation that this decaying carbon gives off, and use it to track the age of items found at Neolithic sites.

Through Carbon dating, we have a better idea of how many people were farming, where, and for how long.

If farming and decaying organic matter started the release of carbon, we know that the industrial era really spiked it.

As you can see in the reaction where octane is combusted, the product, or what is released from the reaction of burning gas, is CO₂, water, and energy.

Fossil fuels are about 81% of U.S. Energy use. That means 81% of our country’s energy comes from reactions like this combustion – releasing CO_2, water, and energy.

Petroleum and natural gas are “hydrocarbons,” meaning they are chain or ring-like molecules containing Hydrogen (H) and Carbon (C).

When we use a car, octane gasoline combusts in the following formula:

2C₈H₁₈ + 25O₂ à 6CO₂ + 18H₂O + Energy

The 81% of energy in the US in post industrial times has made a “normal” fluctuation of CO₂ ppm in our ice age go up. Carbon dating has also allowed us to track the amount of atmospheric carbon through testing sediments, and over the 20,000 year Anthropocene that keeps us alive, the CO₂ levels have fluctuated between 180ppm to 280ppm, normally.

Today, our CO₂ levels are at over 400ppm.

Just like the Mesozoic (remember, when all those plants and animals died?), if our earth were to keep getting hotter, we would trap more greenhouse gas, and the CO₂ ppm would keep going up. We could potentially avert the next glacial period, when the earth is supposed to be covered by 30% ice instead of 10%, and some scientists say that we might already have missed the mark for the beginning of the higher ice percentage in our ice age.

Although, to some, it feels hard to believe, combusting all that gas -- octane -- for a good few decades is changing the makeup of our atmosphere, and perhaps the current trend in our geologic time.
I hope I don’t live to see the end of the Anthropocene.

by Bianca Bowman


Sources:
All of the information comes from my Chemistry notes with Professor Jordan Walk from Chem 103, Fall 2019, and my Geology 101 notes from Professor Jim Kaste, Spring 2018.