What is the Deep Carbon Observatory?
The Deep Carbon Observatory (DCO) is a multidisciplinary, international initiative dedicated to achieving a transformational understanding of Earth's deep carbon cycle, including its poorly constrained reservoirs and fluxes, the unknown role of deep biology, and unexplored influences of the deep carbon cycle on critical societal concerns related to energy, environment and climate.
1. Why study carbon?
Carbon is unique among the chemical elements because of its importance to energy, climate, materials science, environment and health. Carbon forms the backbone of every biomolecule—proteins, carbohydrates, fats and oils, DNA and RNA. When you look at a tree or a whale or any other living thing, you are looking at carbon-based chemical assemblages. Carbon plays many other roles in materials science—carbon chemistry is the basis for every plastic, for paints and glues as well as for dyes and lubricants, for drugs, and, of course, for most of our energy. Carbon is the central element in societal concerns about environment and climate change, as well. And yet, in spite of its importance, we know very little about the nature and extent of carbon inside Earth.
2. What is there to learn about deep carbon? There’s so much we don’t know about deep carbon. For example, studies of meteorites suggest that the material that first formed Earth contained about 3% carbon. Yet, when we add up all the confirmed sources of Earth’s carbon—its life, all its carbonate rocks such as limestone, and the carbon dioxide in the oceans and atmosphere—we find only about 0.1% carbon. Where is the rest? Some of it was probably lost into space as Earth formed, but it’s very possible that significant amounts of carbon are locked into minerals in Earth's deep layers - the mantle and core. By identifying these currently unknown reservoirs, we may be able to increase Earth’s known carbon budget by ten- or twenty-fold.
“Deep life” refers to a fascinating carbon repository and another exciting frontier to explore. We are only just beginning to realize how extensive deep microbial life may be. Drill a hole a mile deep just about anywhere and you will find a sparse, hardy microbial community. These deep microbes, which live in the tiniest cracks and fissures in rocks, survive on the chemical energy of minerals. By some estimates, Earth’s total subsurface biomass may rival all life at the surface—all the ants, elephants, and sequoias included!
There’s also the important question of deep hydrocarbons, especially deep methane or natural gas. Exploratory deep drill holes occasionally find huge deep methane deposits. One must wonder: What is the source of all that methane? Is it all biological, produced by deep microbes? Or might there be even deeper abiotic sources—methane formed by chemical reactions in the lower crust or mantle?
These are three examples of Earth's carbon story that we know we don’t know. However, the most exciting discoveries will likely come from things we don’t realize that we don’t know!
3. How deep is “deep”?The answer depends on the context. “Deep” for life might mean a few meters to a few kilometers beneath Earth's surface, while for carbon-bearing minerals and fluids “deep” also means the lower mantle and core—regions where carbon may play chemical roles that are yet to be discovered. The Deep Carbon Observatory (DCO) thus encompasses the entire planet from crust to core, at scales from nano to global.
4. What is the Deep Carbon Observatory? The Deep Carbon Observatory is a broadly interdisciplinary, international initiative to seek new understanding of carbon, from crust to core, at scales from nano to global. It is a global effort, with participants in 40 different countries, but it’s an observatory in the sense that we need a new generation of observational instruments to make substantial progress. We need new tools to recover deep Earth samples—both rocks and microbes—and we need new analytical instruments and techniques to study those samples. Also required are new high-temperature and high-pressure devices to mimic Earth’s interior conditions in the laboratory and to culture and characterize deep microbes. In addition, we need new theoretical methods to model matter at extreme conditions. All of this and more is our vision for the Deep Carbon Observatory.
5. What do we know about deep life? Studies of drill cores and in deep underground mines reveal that microbial life exists in many crustal rocks at depths of two miles or more below the surface. These hardy microbes are sparse and they live their lives at a remarkably slow pace; some are thought to divide only about once every thousand years. Nevertheless, the volume of the crust is so great that some scientists estimate that the total biomass beneath the surface is almost as large as that of every living thing at the surface.
But even more exciting, we may find totally new kinds of life living at greater depths—at higher temperatures and pressures. It’s possible that Earth’s deepest life doesn’t use DNA and proteins the way normal cells do. There may be living biofilms that just spread along deep cracks and fissures—perhaps as a growing layer of biomolecules. And, since efforts to detect deep life are based on looking for DNA and proteins, we must also develop new techniques to search for deep and potentially weird life.
6. How is carbon related to mineral evolution? “Mineral evolution” refers to the study of the dramatic changes in near-surface mineralogy over the course of Earth history. A central theme of mineral evolution is that life and minerals have co-evolved. Carbon has seen especially remarkable changes in this regard. Models suggest that early Earth had a thick atmosphere of CO2, but few carbon-containing minerals and no life. Today we have thick deposits of limestone and, of course, abundant carbon-rich life. Subsequently, the way that carbon mineralogy has evolved mirrors Earth’s evolution as a living world.
7. Where is the carbon on Mars and other planets? It is likely that all planets and moons have a significant amount of carbon, but thus far our planetary probes have not discovered significant carbon reservoirs. So where is the carbon on Mars or the Moon? What form does it take? Are there limestone deposits, for example, or even carbon-based life forms? These are important questions that will guide astrobiological research in the coming decade. Our growing understanding of Earth’s deep carbon will eventually point to likely reservoirs on other planets, as well.
8. What new scientific instruments are needed for the DCO? Our ability to characterize Earth’s deep carbon is limited in several ways. First, we need access to deep-Earth samples, including drill cores. For example, new technologies are required to recover deep drill cores with pristine in situ microbes that are uncontaminated by drilling fluids. We also need new analytical techniques to characterize carbon-bearing samples of smaller and smaller sizes to determine their molecular structures and isotopic compositions.
We also want to design and construct a new generation of high-temperature and high-pressure devices that can be used to mimic conditions deep inside Earth, all the way to its center (where pressures exceed 3,000,000 atmospheres and temperatures may exceed 5,000 degrees Celsius). We also need to design reactors to culture deep microbes and to study dynamic fluid-rock interactions at conditions of the lower crust and upper mantle. Equally important are new theoretical approaches to model carbon-bearing phases at extreme conditions—studies that will require advances in both computer hardware and software.
9. How can we find out if there is any carbon in Earth’s deep interior? We know there is at least some carbon in the mantle because we find diamonds—crystals of pure carbon that formed at least 100 miles beneath the surface. Diamonds are thought to reach the surface in epic explosive volcanic eruptions, where magmas rise at speeds that may exceed 100 miles per hour! Some of those diamonds also hold tiny inclusions of other minerals—compounds that might hold a small amount of carbon. These mantle samples provide direct evidence for deep carbon.
Studies of deeper carbon reservoirs will rely on a combination of experiment and theory. Experiments on samples at high temperatures and pressures, for example, will reveal how much carbon might alloy with iron in the core, or dissolve in common oxide and silicate minerals in the mantle. Theoretical models of deep carbon will reveal changes in carbon chemistry at extreme conditions and are beginning to point to as yet unknown carbon-bearing minerals in Earth’s mantle and core.
10. Can the Deep Carbon Observatory help to solve the problem of global warming? The DCO wants to achieve a transformational understanding of carbon’s chemical and biological roles in Earth’s interior. Basic knowledge is vitally important as we debate these issues. So, for example, the DCO’s study of CO2 emitted from volcanoes will also contribute to a more basic understanding of the sources and variations in atmospheric CO2, which is an important greenhouse gas.
DCO scientists are also studying the ways that our planet naturally sequesters carbon, for example during the weathering of rocks on the continents and the alteration of rocks on the ocean floor. We do not yet know the amounts and rates of CO2 transfer from the atmosphere to the crust, but our field and lab studies are designed to learn more. Any advances the DCO makes will help us understand how Earth works, and how to deal with excess CO2. For example, we might find new ways to sequester carbon dioxide in the crust. We might also find evidence for new sources of natural gas, a fossil fuel that produces much less CO2per kilowatt-hour than coal or oil, and may thus be the most practical energy source for the coming decades.