Readers Respond to the July 2021 Issue

SEQUESTERING CO₂ IN ROCKS

“The Carbon Rocks of Oman,” by Douglas Fox, described efforts by geologist Peter Kelemen and other scientists to potentially sequester carbon dioxide in mantle rock formations. As a physical chemist who picked up the rudiments of geology and geochemistry during environmental investigations, I was intrigued by the article, which discussed various mechanisms that might be used to enhance the process or lower costs, including both in situ and ex situ concepts.

Would it be possible to use standard petroleum methods such as fracking with high-pressure liquids to improve the permeability of the mantle rocks? And would seawater—which would already be used to sequester CO₂ in Kelemen’s plan—be a candidate for such fracking?

Finally, do the calcium and magnesium in seawater also react with CO₂, especially at the higher pressures and temperatures at depth? And if so, might this tend to “plug up” the veins, natural or induced, before the solution could migrate very far?

Gary McKown West Chester, Pa.

Fox describes a natural process that permanently petrifies CO₂ as magnesium carbonate (MgCO₃) or calcite (CaCO₃) in mantle rock in Oman.

Each CO₂ molecule has two oxygen atoms, whereas there are three in each molecule of MgCO₃ or CaCO₃. If the described process was greatly intensified to rid the atmosphere of CO₂, is there a possibility that we would permanently “lose” too much oxygen? Would we exchange one evil for another?

URSULA GARTENMANN Zurich

FOX REPLIES: In response to McKown’s letter: Injection of CO₂ could indeed potentially be enhanced with artificial fracking using seawater. Pressurized “supercritical” CO₂ could also be a possible fracking fluid.

The calcium and magnesium naturally present in seawater should not increase the tendency of pores in the rock to be clogged with precipitating carbonates. This is because fluids in the water underground already contain calcium and magnesium. The natural carbonation reactions actually involve an initial step in which these elements in the rock dissolve in the CO₂-rich water (which is acidic). Ions of calcium and magnesium then react with the CO₂ and precipitate back into solid minerals.

Gartenmann asks an interesting question. Fortunately, the reactions that convert CO₂ into CO₃ do not consume oxygen gas (O₂). Instead they consume oxygen atoms that are already present in the water and in minerals such as olivines (including Mg₂SiO₄ and Fe₂SiO₄), serpentine [Mg₃Si₂O₅(OH)₄] and brucite [Mg(OH)₂]. Because of the oxygen contents of such minerals, very roughly, Earth’s crust and mantle contain more than a million times more oxygen than the atmosphere!

But even if we were to assume that all of the extra oxygen atoms needed to sequester carbon in rock came from the air, we would lose only a minuscule amount of them: mineralizing a billion metric tons of CO₂ would consume about 0.00003 percent of the estimated 1.2 quadrillion metric tons of O₂ in Earth’s atmosphere. And mineralizing a trillion metric tons of CO₂ would consume only about 0.03 percent of that oxygen.

SCIENCE AND “TRUTH”

In “Is Science Actually ‘Right’?” [Observatory], Naomi Oreskes argues that it offers a process of discovery rather than providing absolute truth.

Science is not really about “right,” “wrong,” “true” or “false.” My work studying Earth’s interior, where observations are always incomplete and often not very accurate, has led me to the idea that theories should be evaluated as more or less “useful within a certain context.” I find this avoids much confusion about what science provides.

For example, Isaac Newton’s theory of gravity was superseded by Albert Einstein’s, but that did not make Newton’s theory “wrong” or make Einstein’s “right.” Newton’s theory is still extremely useful in many contexts. Einstein’s theory is useful in a much broader range of them: it can do a better job of explaining Mercury’s orbit and black holes. If someday a better idea than Einstein’s general theory of relativity comes along, or observations are found that are inconsistent with that theory, then Einstein will not have been “wrong” either.

A physician with a good scientific background will probably be more useful to your health than a typical politician, however prominent. And a climate scientist’s projections into the future are likely to be more useful than those of an ill-informed coal executive. On the other hand, your average shopkeeper may have a better understanding of economies than most neoclassical economists, whose theories bear no useful resemblance to observable economies.

GEOFF DAVIES retired senior fellow, Australian National University

BETTER GUN SAFETY

In “Patient Care Must Include a Gun Talk” [Forum], Chethan Sathya and Sandeep Kapoor argue that doctors should talk to their patients about firearm safety. Doctors are well equipped for good discussions with their patients about exercise, smoking, drug and alcohol consumption, and diet as they relate to health. But few of them, including my doctors, own firearms, and most know little about appropriate firearm safety courses.

I own a firearm and have taken in-person safety courses, which have been invaluable. Doctors would be more effective and trustworthy on this subject if they were better informed about safe gun ownership resources, including local safety courses. For those millions of citizens who are going to own firearms, nothing improves gun safety practices better than a well-taught training course.

ANDREW GOLDSTEIN Portland, Ore.

NEW ERA OF PROTEINS

Your July issue was outstanding. I have never enjoyed reading so many of the articles in any one edition of Scientific American. All of them had important information.

I especially liked “Life, New and Improved,” Rowan Jacobsen’s feature on the creation of artificial proteins and the use of the technology in the development of a new COVID vaccine. I’ve recommended it to my four granddaughters as must reading. One is a research biologist doing work in neuroscience. Two just completed their sophomore years in different colleges, and the fourth will be a senior in high school next year.

J. P. UTTLEY via e-mail

This is, without a doubt, the most intriguing article I have read in this magazine, and I am a long-time subscriber. I’m looking forward to follow-ups because this is obviously the dawn of a new era. I hate the overuse of hyperbolic descriptions, but the superlative fits well here.

STUART TAYLOR Perth, Australia

ERRATUM

“Switchgrass Cleaner,” by Susan Cosier [Advances; August 2021], should have described other researchers using plants to clean up “PCBs,” not “PDBs.”