Where Does the Earth Store All Its Carbon?

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In the public discussion about the climate crisis, you have probably heard about the idea that we need to find efficient technology to actively capture carbon out of the air and store it away. But where? For example, an operation in Iceland has managed to turn atmospheric CO2 into a rock.

All of this may sound revolutionary, but the truth is that humans haven’t done anything nature isn’t already doing. Earth has its own carbon storage system, and now we are looking for a way to hack into it to solve our atmospheric carbon problem.


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How does the Earth’s carbon storage function?

Although all living things are made of and metabolize carbon, most of it is stored in the Earth’s crust and mantle. The atmospheric carbon is just a tiny fragment of the Earth’s overall carbon stash. It is estimated that 1.845 billion billion metric tons of carbon are settled in mantle and crust, while only 43,500 billion tons can be found on the surface. The “loose” carbon is eventually deposited into the Earth’s innards through plate tectonics.

However, carbon escapes from the “storage” in various ways – volcanic activity on land and along the oceanic ridges, wildfires, from soil and lakes, and other minuscule sources. The “loose” carbon is eventually deposited into the Earth’s innards through plate tectonics, so the overall balance stays relatively unaffected.

iagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans.(Diagram adapted from U.S. DOE, Biological and Environmental Research Information System.)
Diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans. (Diagram adapted from U.S. DOE, Biological and Environmental Research Information System.)

Still, larger quantities can be released into the atmosphere during incidental events such as massive volcanic activity or an asteroid impact. The most recent “incidental” driver of carbon in Earth’s geologic history is the direct anthropogenic burning of Earth’s carbon deposits closer to its surface – namely, coal and oil. Currently, human activity releases more than 35 billion metric tons of carbon dioxide per year, reaching a record 37.1 billion metric tons in 2018.

Measuring the Location of Carbon on Earth

Yet the mechanisms behind carbon reservoirs are not entirely known. That is why the international Deep Carbon Observatory has been doing its research. By measuring levels of carbon in rocks that act as a sort of data storage for Earth’s historic carbon levels, they have tried to demystify the planet’s carbon cycles.

The layers revealed records of occasional disturbances – events that overturned the balance and made the carbon levels go significantly up in certain periods. Those historic upsets in carbon levels have been a major focus of the team’s research, as well as the series of papers published in the journal Elements this October. The incidental large-scale release of carbon has proven to have catastrophic effects throughout the geological history, and have been directly tied to climate change and mass extinction events. It is easy to see why they are of special interest today.

Histograms of carbon influx (positive values) and outflux (negative values) to the atmosphere and the oceans. Graph: Suarez, Edmonds, and Jones, 2019.
Histograms of carbon influx (positive values) and
outflux (negative values) to the atmosphere and the oceans. Graph: Suarez, Edmonds, and Jones, 2019.

The most famous example of a carbon-related catastrophy is the dinosaur extinction that took place around 66 million years ago, caused by the impact of the Chicxulub asteroid. The impact didn’t kill the dinosaurs directly – instead, it vaporized carbon-rich rocks, releasing hundreds of billions of tons of CO2 dioxide into the atmosphere.

Before that, 252 million years ago, there was a Permian-Triassic extinction event, very likely tied to a number of magma eruptions – large igneous provinces, which could have released several billion tons of carbon each year during the time of the event. Unfortunately, as pointed out above, today’s human activity releases much, much more.

Research like the one by Deep Carbon Observatory is crucial to make us fully understand the impact and possible consequences of our constant output of Earth’s stored carbon into the atmosphere, as well as to inspire humankind to find solutions and get Earth’s carbon budget back in balance.

References

C.A. Suarez, M. Edmonds and A.P. Jones. (2019). Earth catastrophes and their impact on the carbon cycle. Elements. Vol. 15, October 2019, p. 301. doi: 10.2138/gselements.15.5.301. http://elementsmagazine.org/2019/10/02/earth-catastrophes-impact-carbon-cycle/

“Here’s where Earth stores its carbon.” Science News. October 1, 2019. https://www.sciencenews.org/article/where-earth-stores-its-carbon

“In Iceland, turning CO2 into rock could be a big breakthrough for carbon capture.” PRI. May 3, 2019. https://www.pri.org/stories/2019-05-03/iceland-turning-co2-rock-could-be-big-breakthrough-carbon-capture

“CO2 Emissions Reached an All-Time High in 2018.” Scientific American. December 9, 2018. https://www.scientificamerican.com/article/co2-emissions-reached-an-all-time-high-in-2018/

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