“Deep Carbon” – How Much Does the Earth Have?

Preparing to summarize and celebrate the 10-year Deep Carbon Observatory program, DCO’s Reservoirs and Fluxes team have outlined several key findings that span time from the present to billions of years past; from Earth’s core to its atmosphere, and in size from single volcanoes to the five continents.

Volcanoes, colliding and spreading continental and oceanic plates, and other phenomena re-studied with innovative high-tech tools, provide important fresh insights to Earth’s innermost workings, scientists say.

Among many wide-ranging findings, outlined and summarized in a series of papers published in the journal Elements:

• Just two-tenths of 1% of Earth's total carbon—about 43,500 gigatonnes (Gt) —is above surface in the oceans, on land, and in the atmosphere. The rest is subsurface, including the crust, mantle and core—an estimated 1.85 billion Gt in all.
  
  
• CO2 out-gassed to the atmosphere and oceans today from volcanoes and other magmatically active regions is estimated at 280 to 360 million tonnes (0.28 to 0.36 Gt) per year, including that released into the oceans from mid-ocean ridges.
  
  
• Humanity’s annual carbon emissions through the burning of fossil fuels and forests, etc., are 40 to 100 times greater than all volcanic emissions.
  
  
• Earth’s deep carbon cycle through deep time reveals balanced, long-term stability of atmospheric CO2, punctuated by large disturbances, including immense, catastrophic releases of magma that occurred at least five times in the past 500 million years. During these events, huge volumes of carbon were outgassed, leading to a warmer atmosphere, acidified oceans, and mass extinctions.
  
  
• Similarly, a giant meteor impact 66 million years ago, the Chicxulub bolide strike on Mexico’s Yucatan peninsula, released between 425 and 1,400 Gt of CO2, rapidly warmed the planet and coincided with the mass (>75%) extinction of plants and animals—including the dinosaurs. Over the past 100 years, emissions from anthropogenic activities such as burning fossil fuels have been 40 to 100 times greater than our planet’s geologic carbon emissions.
  
  
• A shift in the composition of volcanic gases from smelly (akin to burnt matches) sulfur dioxide (SO2) to a gas richer in odorless, colorless CO2 can be sniffed out by monitoring stations or drones to forewarn of an eruption—sometimes hours, sometimes months in advance. Eruption early warning systems with real-time monitoring are moving ahead to exploit the CO2 to SO2 ratio discovery, first recognized with certainty in 2014.
  
  

Says DCO scientist Marie Edmonds of the University of Cambridge, UK: “Carbon, the basis of all life and the energy source vital to humanity, moves through this planet from its mantle to the atmosphere.  To secure a sustainable future, it is of utmost importance that we understand Earth’s entire carbon cycle.”

“Key to unraveling the planet’s natural carbon cycle is quantifying how much carbon there is and where, how much moves—the flux—and how quickly, from Deep Earth reservoirs to the surface and back again.”

Adds colleague Tobias Fischer of the University of New Mexico, USA: “The Deep Carbon Observatory has advanced understanding of the inner workings of Earth. Its collective body of more than 1500 publications has not only increased what is known but established limits to what is knowable, and perhaps unknowable.”

“While we celebrate progress, we underline that deep Earth remains a highly unpredictable scientific frontier; we have truly only started to dent current boundaries of our knowledge.”