It Goes On

Model of L-serine molecule

Moments after the Big Bang, the universe contained hydrogen, helium, and trace amounts of lithium. Once stars coalesced, carbon and oxygen were produced.

Carbon and oxygen are synthesized when helium burns inside red giant stars.

Carbon in the universe is traceable to stars

Carbon-based Life

Carbon is the essential ingredient of life-sustaining organic molecules: carbohydrates; proteins; nucleic acids; and lipids.

Carbon allows for bonds that form three-dimensional molecular structures likened to, and modeled by, rings and chains. Such complex molecular structures provide the building blocks of life.

“In three words I can sum up everything I've learned about life: it goes on.”
― Robert Frost

Earth's Carbon

Earth is largely comprised of oxygen and silicon with comparatively little carbon.

Earth exhibits an observable and measurable carbon cycle analogous to a bookkeeper's columnar ledger of debits and credits. Carbon is exchanged between these reservoirs:

• Biosphere - sum of all ecosystems, or life zone;
• Pedosphere - outermost layer of Earth comprised of soil and soil formation;
• Geosphere - solid parts of Earth including, but not limited to, the lithosphere;
• Hydrosphere - combined mass of water on and under the surface of Earth; and
• Atmosphere - layer of gases surrounding Earth retained by Earth's gravity.

Earth's carbon cycle is a model for the ongoing flows between each of the reservoirs. Some carbon flows are slow (e.g., on the order of hundreds of millions of years), while others are fast:

• Slow Carbon Cycle - Over the span of geologic time (100 - 200 million years), chemical reactions, tectonic events, and volcanic events occur that transfers carbon between rocks, soil, ocean, and atmosphere.
• Fast Carbon Cycle - Plants, and phytoplankton in the ocean, absorb carbon dioxide (CO₂) from the atmosphere into their cells via photosynthesis, then return CO₂ via cellular respiration and microbial decomposition.

Fast carbon cycle depicting exchange of carbon between reservoirs

“Originally, the atoms of carbon from which we’re made were floating in the air, part of a carbon dioxide molecule. The only way to recruit these carbon atoms for the molecules necessary to support life—the carbohydrates, amino acids, proteins, and lipids—is by means of photosynthesis. Using sunlight as a catalyst the green cells of plants combine carbon atoms taken from the air with water and elements drawn from the soil to form the simple organic compounds that stand at the base of every food chain. It is more than a figure of speech to say that plants create life out of thin air.”
― Michael Pollan, The Omnivore's Dilemma: A Natural History of Four Meals

Monitoring Earth's Carbon

NASA will launch the Orbiting Carbon Observatory-2 satellite in July 2014. It will record atmospheric CO₂ from space. The data will be used to map CO₂ sources and sinks and to provide insight into its variability over seasonal cycles.

You will die but the carbon will not; its career does not end with you. It will return to the soil, and there a plant may take it up again in time, sending it once more on a cycle of plant and animal life.
― Jacob Bronowski

REFERENCES

• Carbon Cycle, Wikipedia.
• Foundations of Carbon-Based Life Leave Little Room for Error, NC State University Press Release, 13 March 2013.
• Orbiting Carbon Observatory, NASA.
• The Carbon Cycle, Holli Riebeek, Earth Observatory, 16 June 2011.
• What is the Carbon Cycle? What is the science behind it?, United States Carbon Cycle Science Program.