Workers drill into the ground in Wadi Lawayni, a remote valley in Oman. Millions of years ago, unusual rocks were pushed to surface here through a rare geologic upheaval. Now in contact with the air, they are reacting with carbon dioxide, locking the greenhouse gas into solid minerals.

Juerg Matter/Univ. of Southampton

The tired, crumbling peaks of the Al Hajar Mountains are slowly decomposing like a slab of rotten meat. Subtle signs of decay are all around. Flammable hydrogen gas sometimes bubbles from groundwater. Water from natural springs is often saturated with minerals. This water leaves a carpet of frosty white crystals as it flows over the ground. Only a few types of plants can grow in such alien soils.

Here, in the desert nation of Oman, east of Saudi Arabia, the mountains comprise exotic minerals that don’t normally exist at Earth’s surface. They formed dozens of kilometers (miles) below — deeper than humans have ever delved in search of oil or gold. Now exposed to air and water on Earth’s surface, these minerals prove chemically unstable.

When rain falls, it trickles into cracks in the rock, carrying gases from the air. The water and gases react with the rock to form new, colorful minerals. These jagged veins of black, white and blue-green stone push ever deeper into the bedrock. Like slow but powerful fingers, the minerals widen the cracks, prying the rock apart.

Peter Kelemen believes that these decomposing rocks could help humans solve an important problem: climate change.

Kelemen is a geologist at the Lamont-Doherty Earth Observatory in Palisades, N.Y. The white carbonate veins, he notes, formed as carbon dioxide (CO2) in rainwater latched onto magnesium and calcium atoms in the rocks. In other words, these new minerals trap the same gas that humans release when they burn fossil fuels. It’s the same greenhouse gas that is warming our planet.

These unusual rocks are spread across an area of Oman about the size of Maryland. They are naturally petrifying 50,000 to 100,000 tons of CO2 per year, Kelemen believes. That’s puny compared to the 30 billion tons of CO2 that humans release each year. But Kelemen and his colleagues believe these rocks could one day solidify up to a billion tons of CO2 per year. Other rock formations scattered around the world could capture another 10 billion to 20 billion tons of CO2 each year. ”You’re looking at something that could potentially have an impact on the human global carbon budget,” he told me one afternoon in Oman. 

Kelemen and his collaborator, Juerg Matter, have been working on this idea for nearly 20 years. Matter is a geochemist at the University of Southampton in England. When I visited them in Oman in 2018, their team was busy drilling several holes into the rock. They planned to pull up stone from as deep as 400 meters (1,300 feet) underground. Those cores would help them better understand a natural process that they hope to speed up.

Removing CO2 from the air once seemed outlandish. In the last 20 years, however, it has gained momentum as the urgency of climate change has become clearer.

Many scientists now believe people will not reduce releases of greenhouse gases quickly enough to prevent Earth from warming more than 1.5 degrees Celsius (2.7 degrees Fahrenheit). It is thought that this warming limit would avert the most dangerous effects of climate change. Those effects include runaway sea level rise, the loss of the Amazon rainforest and frequent catastrophic storms.

Scientists are now suggesting that people resort to a strategy called “negative emissions.” These would include vast projects to suck billions of tons of CO2 from the air each year. They would need to use many tactics, such as replanting forests. Or fertilizing the ocean to spur the growth of photosynthetic plankton. The forests and plankton would naturally pull CO2 out of the air.

Several companies are also building “direct air capture” machines to pull CO2 from the air. The captured gas could then be pumped underground.

Energy companies have pumped small amounts of CO2 into empty oil and gas reservoirs since the 1980s. There, the gas is trapped between layers of sedimentary rocks, such as sandstone. But if the gas leaks back out, it could cause problems, warns Gregory Nemet. He’s an energy scientist at the University of Wisconsin–Madison. “It doesn’t take a lot,” he says. “If it’s one or two percent leakage, that really puts a hole in our plans to stabilize the climate.”

But different rocks, like those in Oman, could more permanently trap CO2. They contain high levels of calcium and magnesium silicates. In these minerals, calcium and magnesium atoms are bound to clusters of oxygen and silicon atoms, called silica. These minerals, uncommon at Earth’s surface, are plentiful in rocks very deep below ground. Scientists had suspected these minerals would react with CO2 and lock it into carbonate minerals. This idea lured Matter to get involved. He wanted to test it.

Matter had just gotten his PhD when he took a job at Lamont-Doherty back in 2001. The campus sits in a forest near New York City. The buildings stand above cliffs that drop 100 meters (325 feet) into the Hudson River. Those chocolatey brown cliffs are made of stone known as basalt. It formed from lavas that erupted millions of years ago from deep inside Earth.

Basalts contain calcium and magnesium silicates. David Goldberg, the geophysicist who hired Matter, wanted him to try injecting CO2 into them.

”Everybody thought I’m crazy, and even stupid,” for trying this, recalls Matter. Other scientists had done lab experiments. Their data suggested carbonate minerals would take hundreds of years to form. That would be far too slow to attack today’s climate-change threat.

But in 2004, Matter and Goldberg tried anyway. They injected water 230 meters (750 feet) down a well drilled into the basalt. That water contained a few kilograms (maybe 5 pounds) of CO2.

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When Matter pumped the water back out a week later, the CO2 had vanished. This gas forms a weak acid in water. The acid dissolved some of the calcium and magnesium silicates in the rocks. They reacted with the gas to form carbonates. And this was happening 300 to 3,000 times more quickly than in lab tests. The team published its findings back in 2007.

“Thinking back, it was quite high risk what we did,” says Matter. There was a big chance that it wouldn’t work. “We just believed in it,” he says. And, he adds, “We were really just lucky.”

Matter and several other scientists then went looking for other places to turn CO2 into stone — and on a much bigger scale. In 2012, they got their chance.

Iceland is an island nation in the north Atlantic Ocean. Reykjavik Energy, there, ran a geothermal power plant near one of the country’s many volcanoes. The company wanted to dispose of CO2. Its plant generated electricity using hot water gushing up from underground. Volcanoes often spew CO2. As the water emerged from below ground, it too released this gas into the air.

But there was an obvious solution. Iceland is made almost entirely of basalt. Injecting CO2 into that basalt should lock it away.

In 2012, workers drilled a hole in a grassy field near the power plant and injected water 400 meters (1,300 feet) into the basalt below. This water held six times as much CO2 as seltzer water does. To prevent it from fizzing violently as the gas escaped, the water had to be kept under high pressure. Over several weeks, the team injected 71 metric tons (78 U.S. tons) of CO2 into the rock.

Meanwhile, Sandra Snæbjörnsdóttir (SNY-byorns-DOT-er) pumped water from another nearby hole. She’s a geologist who was working on this project, known as Carbfix. She found that the CO2 was disappearing from the injected water as it seeped through the rocks. “It happened actually faster than we dared to hope,” she says.

Over 95 percent of the CO2 formed minerals — solid rock — within two years. The team drilled a new hole and retrieved stone cores from near the injection site. The cylinders of gray-black basalt were splotched with white. Those splotches were the carbonate minerals formed by the injected CO2. These results appeared in Science in 2016.

The project is now petrifying 10,000 tons of CO2 per year. And Carbfix has become a separate company, with plans to expand its operations.

“You can actually stuff quite a lot of CO2 into these rocks,” says Snæbjörnsdóttir, who now works for the new company. She estimates that a cubic meter of basalt (a block the size of a dishwasher) can absorb more than 100 kilograms (220 pounds) of CO2. Basaltic rock also sits beneath most of the world’s seafloors. Not all of that rock is suitable for petrifying CO2. But some of it seems to be. Snæbjörnsdóttir predicts that Carbfix will eventually try injecting CO2 into these oceanic basalts off the coast of Iceland.

Matter oversaw the initial Carbfix experiments. But even before those first injections, he was already looking for more places to solidify CO2.

In 2007, he and Kelemen started looking at the rocks in Oman. These rocks come from the mantle. That’s the middle layer of our planet. Humans have never directly seen it. The mantle starts about 10 kilometers (6 miles) below the seafloor and reaches 2,900 kilometers (1,800 miles) into the Earth. The Oman rocks were a tiny fragment of mantle that had been shoved up to the surface. It happened millions of years ago during a rare geologic upheaval.

The mantle is the source of lava and basalts. Its rocks contain even higher levels of calcium and magnesium silicates than do basalts. Because of this, Matter and Kelemen believed that the Oman rocks might be able to trap more CO2 per cubic meter than the rocks in Iceland.

Mantle rocks on the surface of the Al Hajar Mountains are crisscrossed with white carbonate veins. Matter and Kelemen used radiocarbon dating to show that some of those veins were less than 5,000 years old. This suggested these rocks hadn’t just absorbed CO2 millions of years ago — they were doing so right now. Matter and Kelemen published those findings in 2008.

The two scientists still needed to learn more about what was happening below the surface. So in 2017 and 2018, they and a large team of researchers drilled several holes in Oman to retrieve stone cores. I spent a week with them in January 2018 as they drilled in a remote valley, Wadi Lawayni (WAH-dee Lah-WAY-nee).

On a late afternoon, several camels wandered past, chewing on scraggly bushes. A diesel engine roared. And a metal drill shaft, driven by that engine, spun several thousand times per second as it cut into the rocks beneath our feet.

Now and then, workers in hard hats idled the motor to a low growl. Then they raised the drill from the hole, detached a metal pipe and slid out three meters (9.8 feet) of cored rock.

The cylinders of stone were as thick as a baseball bat. After laying them out on tables, Kelemen, Matter and several other scientists examined them.

The gray stone was crisscrossed with white, black, orange-yellow and blue-green minerals. These veins marked where water and gases, seeping through cracks, had reacted with the stone.

Oxygen reacted with iron in the rock — literally “rusting” it — to create yellow and orange veins. Black, blue and green veins often were a mineral called serpentine. It forms when water reacts with silicates. And the white veins were usually carbonate minerals — although not always. I watched as Elisabetta Mariani ran a quick test on a vein to identify the mineral.

Mariani is a geologist at the University of Liverpool in England. Using a lighter, she held a flame against the vein for several seconds. Then, with a plastic bottle in hand, she squeezed several drops of acid onto it. The heated part of the vein fizzed like seltzer water for several seconds. As it reacted with the acid, the rock was releasing tiny bubbles of CO2.

“This is magnesite,” she said — magnesium carbonate.

These carbonate veins were plentiful in the top 15 meters (50 feet) of core. They were often as thick as a finger. Farther down, they thinned and became less frequent. Below 100 meters (330 feet), there were none.

This confirmed what Matter had long suspected. “All of the CO2 is mineralized in the very shallow part,” he says. Once rainwater has seeped in, it may spend many years underground. But all of its CO2 is consumed right at the beginning.

Matter and Kelemen now think the rate of carbonate formation could be boosted — and by a lot. Someday, they envision CO2 being pressurized into water at 125 times rainwater’s natural concentration (about 6 times that of seltzer water). This mix would then be pumped three kilometers (almost two miles) underground. Rocks there are close to 100 °C (212 °F). The high heat and pressure would speed up the chemical reactions that turn CO2 to stone.

This is many years away.

But the first baby steps are starting. Late in 2020, an Omani company named 44.01 was set up. (It is named after the average weight of a molecule of CO2.) The company’s goal is to trap CO2 in mantle rocks in Oman.

”We are aiming for one gigaton,” said Talal Hasan, shortly after 44.01 was formed. He is the company’s founder. By “gigaton,” he means a billion tons per year.

The first field test was, of course, quite small. Last September, workers injected about 240 kilograms (530 pounds) of CO2 into one of the boreholes in Wadi Lawayni. A month later, Matter pulled some water samples out of another hole a few meters away.

Matter is still analyzing that water. But he hopes to find evidence that the mix of CO2 and water is reacting with the rock. “This test is just to demonstrate on a field scale that the reaction is fast enough,” he says. Later, larger tests will see if the newly forming carbonates are prying the rock apart, as expected. Both Matter and Kelemen are giving the company scientific advice.

But the long-term success of their vision will depend on more than just scientific results. It will also depend on the decisions of governments around the world.

Companies like 44.01 and Carbfix can only turn CO2 to stone if someone will pay them to do it.

Before CO2 can be injected underground, it first has to be captured from the air. And the tech to capture CO2 is not cheap. Still, Nemet predicts that the cost of direct air capture will come down over time (as it has for other technologies, such as wind power).

Even if someone is willing to pay for it, turning CO2 into stone will require a lot of work. Companies like Carbfix and 44.01 might take 20 years to work their way up to injecting gigatons of CO2 per year. And the operations needed to do that will be truly massive.

Kelemen estimates that trapping a billion tons of CO2 per year in Oman might require 5,000 injection wells. Those wells would need to pump a combined 23 cubic kilometers of water into the ground each year. That’s equal to about one quarter the annual flow of the Missouri River. Because Oman is a desert nation, this water would have to come from the ocean.

Gathering a billion tons of CO2 per year from the air would require thousands of machines, each about the size of a truck. Together, they could devour up to 1.3 trillion kilowatt hours of electricity per year. That’s three times the amount of electricity consumed by the entire state of Texas. To avoid gushing more CO2 into the air, this electricity would need to come from a renewable source — such as wind or solar — not fossil fuels.

Fortunately, Oman gets plenty of sunshine. Some 600 square kilometers (230 square miles) of solar collectors could supply the electricity needed. That’s about one five-hundredth of Oman’s land area. “It’s not insurmountable,” says Ajay Gambhir. “But it’s a bit of a challenge,” notes this energy economist. He works at Imperial College London in England.

By 2050, people would need to remove up to 20 billion tons of CO2 from the skies each year. That would require 20 of these massive operations — or hundreds of smaller ones — working across the globe.

Gambhir views these technologies as an important “insurance policy.” Perfecting them will take years. But if we get to 2040 and CO2 emissions are still high, then it will be too late at that point to start working on them, he says. “Doing it now is the right thing to do.”

alien: A non-native organism. (in astronomy) Life on or from a distant world.

annual: Adjective for something that happens every year. (in botany) A plant that lives only one year, so it usually has a showy flower and produces many seeds.

Atlantic: One of the world’s five oceans, it is second in size only to the Pacific. It separates Europe and Africa to the east from North and South America to the west.

atmosphere: The envelope of gases surrounding Earth, another planet or a moon.

atom: The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

average: (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

basalt: A type of black volcanic rock that tends to be very dense (unless volcanic eruptions seeded it with lots of air pockets). 

bedrock: The thick, solid rock layer than underlies the soil and other broken, rocky materials on Earth’s surface.

borehole: A hole drilled deep into the ground to extract a core of soil, ice or rock. Sometimes the hole is drilled with the goal of getting to gas or pools of liquid, such as water or crude oil.

calcium: A chemical element and alkali metal common in minerals of the Earth’s crust and in sea salt. It is also found in bone mineral and teeth, and can play a role in the movement of certain substances into and out of cells.

carbon: A chemical element that is the physical basis of all life on Earth. Carbon exists freely as graphite and diamond. It is an important part of coal, limestone and petroleum, and is capable of self-bonding, chemically, to form an enormous number of chemically, biologically and commercially important molecules. (in climate studies) The term carbon sometimes will be used almost interchangeably with carbon dioxide to connote the potential impacts that some action, product, policy or process may have on long-term atmospheric warming.

carbon dioxide: (or CO2) A colorless, odorless gas produced by all animals when the oxygen they inhale reacts with the carbon-rich foods that they’ve eaten. Carbon dioxide also is released when organic matter burns (including fossil fuels like oil or gas). Carbon dioxide acts as a greenhouse gas, trapping heat in Earth’s atmosphere. Plants convert carbon dioxide into oxygen during photosynthesis, the process they use to make their own food.

carbonate: A group of minerals, including those that make up limestone, which contains carbon and oxygen.

chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemical reaction: A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).

climate: The weather conditions that typically exist in one area, in general, or over a long period.

climate change: Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

colleague: Someone who works with another; a co-worker or team member.

concentration: (in chemistry) A measurement of how much of one substance has been dissolved into another.

core: Something — usually round-shaped — in the center of an object. (in geology) Earth’s innermost layer. Or, a long, tube-like sample drilled down into ice, soil or rock. Cores allow scientists to examine layers of sediment, dissolved chemicals, rock and fossils to see how the environment at one location changed through hundreds to thousands of years or more.

crystal: (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.

electricity: A flow of charge, usually from the movement of negatively charged particles, called electrons.

engine: A machine designed to convert energy into useful mechanical motion. Sometimes an engine is called a motor. (in computer science) A computer program that performs a particular, narrow range of functions.

exotic: An adjective to describe something that is highly unusual, strange or foreign (such as exotic plants).

field: An area of study, as in: Her field of research is biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.

flammable: Something that can burn (go up in flames) easily.

forest: An area of land covered mostly with trees and other woody plants.

fossil fuel: Any fuel — such as coal, petroleum (crude oil) or natural gas — that has developed within the Earth over millions of years from the decayed remains of bacteria, plants or animals.

geochemistry: A science that deals with the chemical composition of and chemical changes in the solid material of Earth or of another celestial body (such as the moon or Mars). Scientists who study geochemistry are known as geochemists.

geologic: An adjective that refers to things that are related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

geophysics: A field of science that applies and focuses on the principles of physics (energy and forces) to the study of Earth and to similar structures in other celestial bodies (such as exoplanets). People who work in this field are known as geophysicists.

greenhouse gases: Gases that contribute to the greenhouse effect by absorbing heat. Carbon dioxide and methane are two examples of such gases.

groundwater: Water that is held underground in the soil or in pores and crevices in rock.

hydrogen: The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues. It’s made of a single proton (which serves as its nucleus) orbited by a single electron.

Iceland: A largely arctic nation in the North Atlantic, sitting between Greenland and the western edge of Northern Europe. Its volcanic island was settled between the late 800s and 1100 by immigrants from Norway and Celtic lands (ones governed by the Scots and Irish). It is currently home to roughly a third of a million people.

iron: A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

lava: Molten rock that comes up from the mantle, through Earth’s crust, and out of a volcano.

literally: A term that the phrase that it modifies is precisely true. For instance, to say: "It's so cold that I'm literally dying," means that this person actually expects to soon be dead, the result of getting too cold.

magnesium: A metallic element that is number 12 on the periodic table. It burns with a white light and is the eighth most abundant element in Earth’s crust.

magnesium carbonate: A white solid mineral. Each molecule consists of a magnesium atom linked to a group with one carbon and three oxygen atoms. It is used in fireproofing, cosmetics and toothpaste. Climbers and gymnasts dust magnesium carbonate as a drying agent on their hands to improve their grip.

mantle: (in geology) The thick layer of the Earth beneath its outer crust. The mantle is semi-solid and generally divided into an upper and lower mantle.

metal: Something that conducts electricity well, tends to be shiny (reflective) and is malleable (meaning it can be reshaped with heat and not too much force or pressure).

mineral: Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.

momentum: A measure of the motion of something, made by multiplying its mass and velocity. Changing the speed or direction of an object will also alter its momentum.

motor: A device that converts electricity into mechanical motion. (in biology) A term referring to movement.

oxygen: A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.

plankton: (sing. plankter) Small organisms that largely drift or float in the sea. Depending on the species, plankton range from microscopic sizes to organisms about the size of a flea. Some are tiny animals. Others are plant-like organisms. Although an individual plankter is very small, these organisms often form massive colonies, numbering in the billions. The largest animal in the world, the blue whale, lives on plankton.

plastic: Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation. (adj.) A material that is able to adapt by changing shape or possibly even changing its function.

power plant: An industrial facility for generating electricity.

pressure: Force applied uniformly over a surface, measured as force per unit of area.

radiocarbon dating: Short for radioactive-carbon dating or simply carbon dating. A way to measure the age of organic materials — ones containing carbon. Carbon 14, a weakly radioactive isotope, forms in Earth’s upper atmosphere as cosmic rays hit nitrogen atoms. This carbon joins with oxygen to form carbon dioxide, which living organisms take up and incorporate in their tissues. When those organisms die, they stop exchanging carbon with the environment and the share of the C14 isotope starts to fall at a constant rate (one set by the law of radioactive decay). By measuring the share of C14 in the organism’s remains, scientists can determine how long ago it died.

rainforest: Dense forest rich in biodiversity found in tropical areas with consistent heavy rainfall.

renewable: An adjective for resources that can be endlessly replaced (such as water, green plants, sunlight and wind). This is in contrast to non-renewable resources, for which there is a finite supply -- one that can essentially be used up. These include petroleum (and other fossil fuels) or relatively rare elements and minerals.

reservoir: (in geology) A large store of something (such as groundwater) or the structure that serves as the storage container.

risk: The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

sandstone: A type of sedimentary rock. It formed as sand-size grains of mineral grit became compacted or glued together over time.

sea: An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

sea level: The overall level of the ocean over the entire globe when all tides and other short-term changes are averaged out.

sedimentary rock: A type of rock that forms from accumulated material that has been eroded from other rocks. It often forms from mud, sand, or clay gathered at the bottom of an ocean, lake, or river.

serpentine: Relating to serpents or snakes.

silica: A mineral, also known as silicon dioxide, containing silicon and oxygen atoms. It is a basic building block of much of the rocky material on Earth and of some construction materials, including glass.

silicate: A mineral containing silicon atoms and usually oxygen atoms. The majority of Earth’s crust is made of silicate minerals.

silicon: A nonmetal, semiconducting element used in making electronic circuits. Pure silicon exists in a shiny, dark-gray crystalline form and as a shapeless powder.

solar: Having to do with the sun or the radiation it emits. It comes from sol, Latin for sun.

strategy: A thoughtful and clever plan for achieving some difficult or challenging goal.

technology: The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

Texas: The second largest state in the United States, located along the southern border with Mexico. It is about 1,270 kilometers (790 miles) long and covers an area of 696,000 square kilometers (268,581 square miles).

trillion: A number representing a million million — or 1,000,000,000,000 — of something.

vein: (in geology) A mineral or ore deposit in rock that typically runs a long distance and may contain enough material to be worth extracting, such as a silver vein.

volcano: A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations. This plumbing system can become more complex over time. This can result in a change, over time, to the chemical composition of the lava as well. The surface around a volcano’s opening can grow into a mound or cone shape as successive eruptions send more lava onto the surface, where it cools into hard rock.

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Journal: P.B. Kelemen et al. Engineered carbon mineralization in ultramafic rocks for CO2 removal from air: Review and new insights. Chemical Geology. Vol. 550, September 20, 2020. doi: 10.1016/j.chemgeo.2020.119628.

Journal: D.E. Clark et al. CarbFix2: CO2 and H2S mineralization during 3.5 years of continuous injection into basaltic rocks at more than 250 °C. Geochimica et Cosmochimica Acta. Vol. 279, April 8, 2020 online, p. 45. doi: 10.1016/j.gca.2020.03.039.

Journal: J.M. Matter et al. Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions. Science. Vol. 352, June 10, 2016, p. 1312. doi: 10.1126/science.aad8132.

Journal: P.B. Kelemen & G. Hirth. Reaction-driven cracking during retrograde metamorphism: Olivine hydration and carbonation. Earth and Planetary Science Letters. Vol. 345-348, 2012, p. 81. doi: 10.1073/pnas.0805794105.

Journal: P.B. Kelemen & J. Matter. In situ carbonation of peridotite for CO2 storage. Proceedings of the National Academy of Sciences. Vol. 105, November 11, 2008, p. 17295. doi: 10.1073/pnas.0805794105.

Journal: D.S. Goldberg et al. Carbon dioxide sequestration in deep-sea basalt. Proceedings of the National Academy of Sciences. Vol. 105, July 22, 2008, p. 9920. doi: 10.1073/pnas.0804397105.

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Douglas Fox is a freelance journalist who writes about life, earth and Antarctic sciences.

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