MIT Discovers Tectonic Clay's Ability to Efficiently Trap Organic Carbon, Leading to Global Cooling

Scientists at MIT have identified a clay mineral known as smectite that can effectively capture carbon and potentially affect the global climate over time periods spanning millions of years. The research indicates that this mineral has likely played a role in causing ice ages throughout history, and it could potentially be useful in future efforts to mitigate climate change. The study's findings were first published in SciTechDaily.com.

Smectite is a certain clay known for its accordion-textured surface. The clay can effectively capture and store carbon dioxide, which could help counteract global warming over time.

MIT scientists show that smectite, a clay mineral found on the seafloor, is surprisingly adept at capturing and storing carbon for millions of years. Under microscopic examination, the clay has a structure resembling an accordion's folds. These folds are known for effectively trapping organic carbon.

The team from MIT demonstrated that carbon-capturing clay is the product of tectonic movement. When the oceanic crust collides with a continental plate, it brings rocks to the surface, which over time can break down into various minerals, including smectite. Eventually, the clay sediment returns to the seafloor, where the minerals trap bits of decayed organisms within their microscopic folds. As a result, the organic carbon is prevented from being consumed by microbes and released back into the air as carbon dioxide.

Over millions of years, smectite can potentially have a global impact, helping to decrease the earth's temperature. The researchers determined that smectite was likely created following several significant tectonic events within the past half-billion years. During each tectonic incident, the clays trapped enough carbon to induce an ice age.

These encouraging findings are a first, demonstrating the potential of plate tectonics to cause ice ages via the generation of carbon-trapping smectite.

The MIT team indicates that tectonic activity leads to the formation of smectite clay, which can capture a surprising amount of organic carbon. This happens across millions of years.

Today, these clays are found in certain areas with active tectonic activity. The research team suggests that smectite clay continues to capture carbon, contributing to a natural albeit slow, defense against climate-warming human activities.

MIT graduate student Joshua Murray states that the impact of these clay minerals is significant and has implications for sustaining life on planets. He discusses potential modern uses of these clays in offsetting some of the carbon humans have released into the atmosphere.

These research findings were published in the Nature Geoscience journal on November 30 by researchers Murray and Oliver Jagoutz, an MIT professor of geology.

Preliminary research conducted by the team suggested that tectonic action in tropic regions was likely behind each of the Earth's major ice ages. They have investigated this link further and demonstrated the mechanism through which tectonic activity could generate carbon-trapping minerals in sufficient quantities to prompt a global ice age.

The team studied geological literature and data, created a simulation based on their findings, and analyzed the impact of different rock types exposed as a result of tectonic collisions. The research involved studying rock weathering and the minerals that form as a result of this activity.

Finally, these weather-eaten minerals were used in a simulated earth carbon cycle to determine the effect of carbon interaction with organic and inorganic forms of carbon.

From these analyses, one mineral had a clear presence and effect: smectite. Not only was the clay a naturally weathered product of tropical tectonics, it was also highly effective at trapping organic carbon. In theory, smectite seemed like a solid connection between tectonics and ice ages.

But were enough of the clays actually present to trigger the previous four ice ages? Ideally, researchers should confirm this by finding smectite in ancient rock layers dating back to each global cooling period.

“Unfortunately, as clays are buried by other sediments, they get cooked a bit, so we can’t measure them directly,” Murray says. “But we can look for their fingerprints.”

The team reasoned that, as smectites are a product of ophiolites, these ocean rocks also bear characteristic elements such as nickel and chromium, which would be preserved in ancient sediments. If smectites were present in the past, nickel and chromium should be as well.

To test this idea, the team looked through a database containing thousands of oceanic sedimentary rocks that were deposited over the last 500 million years. Over this time period, the Earth experienced four separate ice ages. Looking at rocks around each of these periods, the researchers observed large spikes of nickel and chromium, and inferred from this that smectite must also have been present.

By their estimates, the clay mineral could have increased the preservation of organic carbon by less than one-tenth of a percent. In absolute terms, this is a minuscule amount. But over millions of years, they calculated that the clay’s accumulated, sequestered carbon was enough to trigger each of the four major ice ages.

“We found that you really don’t need much of this material to have a huge effect on the climate,” Jagoutz says.

“These clays also have probably contributed some of the Earth’s cooling in the last 3 to 5 million years, before humans got involved,” Murray adds. “In the absence of humans, these clays are probably making a difference to the climate. It’s just such a slow process.”

“Jagoutz and Murray’s work is a nice demonstration of how important it is to consider all biotic and physical components of the global carbon cycle,” says Lee Kump, a professor of geosciences at Penn State University, who was not involved with the study. “Feedbacks among all these components control atmospheric greenhouse gas concentrations on all time scales, from the annual rise and fall of atmospheric carbon dioxide levels to the swings from icehouse to greenhouse over millions of years.”

Could smectites be harnessed intentionally to further bring down the world’s carbon emissions? Murray sees some potential, for instance, to shore up carbon reservoirs such as regions of permafrost. Warming temperatures are predicted to melt permafrost and expose long-buried organic carbon. If smectites could be applied to these regions, the clays could prevent this exposed carbon from escaping into and further warming the atmosphere.

“If you want to understand how nature works, you have to understand it on the mineral and grain scale,” Jagoutz says. “And this is also the way forward for us to find solutions for this climatic catastrophe. If you study these natural processes, there’s a good chance you will stumble on something that will be actually useful.”

Reference: “Palaeozoic cooling modulated by ophiolite weathering through organic carbon preservation” by Joshua Murray, and Oliver Jagoutz, 30 November 2023, Nature Geoscience. DOI: 10.1038/s41561-023-01342-9

This research was funded, in part, by the National Science Foundation.