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Deep Earth Hosts 15 to 23 Billion Tonnes of Carbon - Hundreds of Times More Than Humans

By: April Carson

Microorganisms that barely survive as "zombie" bacteria and other forms of life account for an enormous quantity of carbon down deep within Earth's subsurface—245 to 385 times more than the carbon content of all humans on the surface, according to researchers nearing the conclusion of a ten-year worldwide effort to unveil Earth's innermost mysteries.

Even in the deepest subsurface, bacteria, archaea, and other creatures—some of them zombies—exist that are stranger than their surface counterparts.

Underground dwellers account for between 70% and 99% of Earth's bacteria and archaea.

The subsurface of other planets could conceivably be inhabited by microbes, according to Earth's deep life.

Carbon deep inside the planet's subsurface exists in a form barely perceptible to humans—bacteria and other life forms that are barely alive. According to scientists who are nearing completion of a 10-year worldwide effort to reveal Earth's innermost secrets, it is 245 to 385 times greater than all human carbon on the surface.

On the day before the annual meeting of the American Geophysical Union, researchers with the Deep Carbon Observatory revealed several transformational discoveries, including how much and what kinds of life exist in the deep subsurface under the most severe forms of pressure, temperature, and limited energy and nutrient availability.

The researchers drilled 2.5 kilometers into the ocean floor and collected microbes from continental mines and boreholes more than 5 kilometers deep in order to develop ecosystem models deep within the planet based on their findings.

They have estimated the size of the deep biosphere—2 to 2.3 billion cubic kilometers (nearly twice the volume of all oceans)—as well as the carbon mass of deep life: 15 to 23[1] billion tonnes (an average of at least 7.5 tonnes of carbon per cu km subsurface).

The research also aids in the identification of extraterrestrial environments that may be home to life.

Among many other discoveries and ideas:

  • The deep biosphere is a vast subterranean "Galapagos" that includes bacteria and archaea (microbes without a membrane-bound nucleus), as well as eukarya (microbes or multicellular organisms with cells containing a nucleus and membrane-bound organelles).

  • Bacteria and archaea are the primary forms of life in Deep Earth. They number in the millions, with many more yet to be discovered or identified. This so-called "microbial dark matter" adds a whole new dimension to our understanding of life. According to Life Scientists, around 70% of Earth's bacteria and archaea dwell in the subsurface.

  • Microorganisms living deep in the ground are often very different from their surface counterparts, with life cycles that span near-geologic time periods and feed on energy from rocks in some cases.

  • The genetic diversity of organisms that dwell beneath the surface is nearly identical to or surpasses that which lives above it.

  • Despite the fact that subsurface microbial communities vary considerably by location, several genera and higher taxonomic categories are ubiquitous – they may be found on every continent.

  • Microbial community richness is an indication of the age of marine sediments where cells are found—which implies that food energy has decreased over time, reducing the microbial community in older sediments.

  • The precise limits of Earth's temperature, pressure, and energy availability have yet to be discovered. Records are broken all the time. Geogemma barossii, a single-celled organism that lives in hydrothermal vents on the sea floor and is considered to be Earth's hottest living thing, has an absolute limit of 121 degrees Celsius, but often grows at 113 degrees Celsius, just shy of its limit.

  • The highest temperature at which a microbe can live is 122°C, according to laboratory studies. (Compared to the hottest place on Earth's surface in an uninhabited Iranian desert, which is about 71°C—the temperature of well-done steak)

  • Approximately 5 kilometers is the record depth at which life has been discovered in the continental subsurface; the record in marine waters is 10.5 kilometers from the sea surface, a pressure of extreme pressure; for example, at 4000 meters depth, pressure is roughly 400 times greater than at sea level.

  • The consequences of human activity on life in subterranean regions have been studied more thoroughly (e.g., fracked shales, carbon capture and storage).

DNA sequencing is becoming more accurate and cheaper, and breakthroughs in deep ocean drilling techniques (developed on the Japanese scientific vessel Chikyu, intended to eventually drill far beneath the seabed in some of the planet's most seismically-active areas) allowed researchers to examine the structure of the deep biosphere for the first time.

There are comparable projects to delve ever deeper into continental settings, utilizing sampling equipment that maintains pressure in order to preserve microorganisms (none expected to cause any health risk or benefit).

For example, the group compiled data on cell concentration and microbial diversity from locations all around the world to calculate the total weight of Earth's subterranean deep life, such as mollusks or rotifers.

The researchers took into account a range of factors, such as global heat flow, surface temperature, depth and lithology—the physical features of the rocks in each area—to determine that the continental subsurface contains 2 to 6 × 1029 cells.

The total amount of global Deep Earth biomass is roughly 15 to 23 petagrams (15 to 23 billion tonnes) of carbon, according to estimates of subsurface life under the seas.

“The Amazon rainforest is comparable to exploring the deep subsurface,” says Mitch Sogin of the Marine Biological Laboratory in Woods Hole, USA, co-chair of DCO's Deep Life community of more than 300 researchers from 34 countries. There is life all around us, and it's exciting. There are so many different species that there is always something new to discover.

Molecular studies suggest that microorganisms dark matter is considerably more diverse than we currently realize, and the deepest branching lineages refute the three-domain theory put forth by Carl Woese in 1977. “We may be approaching a nexus where the most feasible branching patterns might be revealed through comprehensive life research,” concludes Professor Nunez.

“We didn't know much about the bacteria and microorganisms that dominate the subsurface biosphere ten years ago,” explains Karen Lloyd of University of Tennessee at Knoxville. “Today, we know that in many regions, they invest the majority of their time and effort to merely maintaining their existence rather than developing it, which is an intriguing way to live.”

“We now know that subsurface life is widespread. We had only investigated a few locations—types of locations where we would expect to find life—ten years ago. Now, thanks to ultra-deep sampling, we know that they can be found almost everywhere, albeit in an infinitesimal quantity of the deep biosphere.

"Our research of deep biosphere organisms has generated a great deal of new information, but it has also brought to light how much more we have to learn about subsurface life," says Rick Colwell, Oregon State University in the United States. “For example, we don't yet know all of the ways that deep subsurface life affects surface life and vice versa. And we may only stare in awe at the natural metabolisms that allow creatures to live under such harsh and forbidding conditions for life on Earth now.”

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About the Blogger:

April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on

To read more of April's blogs, check out her website! She publishes new blogs on a daily basis, including the most helpful mommy advice and baby care tips! Follow on IG @bossbabymav







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