Of all the ideas that circulated during the recent American Geophysical Union meeting at the Moscone Center, one of the most outlandish-sounding schemes was from a San Francisco entrepreneur who claims he can help conquer climate change by sprinkling pebbles on tropical beaches.

The proposal appears, to the uninitiated, to be a first-class boondoggle, but California’s top climate scientists not only support the notion that rocks can sequester carbon, they are clamoring for viable experiments to test the theory.

Eric Matzner, who co-founded the nonprofit Project Vesta this year, intends to mine tons of a soft, crumbly green volcanic stone called olivine, grind it into pebbles and spread it on shorelines, coves and beaches, where the wave action will weather it down like a river sculpts gravel.

Scientists say the process of erosion chemically alters the acidic molecules in seawater and converts carbon dioxide into bicarbonate, thereby taking the heat-trapping gases out of circulation and reversing acidification, one of the primary concerns of global warming. The more the rock breaks down, the more carbon dioxide is taken out of the sea.

It is a natural process that is believed to occur faster in the tropics, where warmer temperatures help the dissolution process. That explains Matzner’s desire to do a trial run there.

Scientists say the periodic exposure to the elements of big chunks of volcanic rock as a result of tectonic movement has, over a geologic time scale, influenced the Earth’s climate, even helping bring on ice ages.

That’s because volcanic rocks are alkaline and react to the carbon dioxide in the atmosphere. Scientists have found that grinding the rocks, like the surf does, increases the reactive surface area of the particles, stimulating consumption of CO2.

What Matzner and his scientific adviser, Francesc Montserrat, a marine ecologist in the Netherlands, want to do is speed up the natural process by doing what climate scientists call “enhanced weathering,” essentially rubbing off the oxidation layer built up over time that prevents the molecules from reacting.

“We’re intervening,” Matzner said. “We’re accelerating Earth’s natural process of carbon renewal. In the grand scheme of things, we are putting the carbon in the atmosphere back into rock.”

The plan is to raise $1 million to $1.5 million and use it to collect the stone, grind it into pebbles and pour it on a shoreline, creating an olivine beach. The pilot program would determine the least expensive, most energy-efficient way to accomplish the task, including mining, transport and distribution. The research would compare the amount of carbon dioxide removed to how much is produced by the process.

The Project Vesta team, which has so far raised about $100,000, chose olivine, which is made of magnesium and silica, because “it’s the fastest weathering silicate,” Matzner said. The gemstone, commonly known as peridot, the August birthstone, is also extremely abundant. It is often found in the tailings left over from the mining of diamonds and other minerals.

“There is enough olivine to remove all human emissions, ever,” Matzner said. “We think this is a viable method to remove CO2 on a large scale.”

According to a special report by the U.N. Intergovernmental Panel on Climate Change released in September, more than 90% of the heat and 20% to 30% of the carbon dioxide from cars and factories is absorbed by the ocean. This causes the water to lose oxygen and become more acidic, which has devastating consequences for marine life.

Montserrat, a senior environmental engineer at a dredging company in the Netherlands, said he has been studying ways to recapture carbon since 2011.

He and a colleague conducted experiments in 2016 on Papakolea Beach, a natural olivine beach famous for its green sand, on the Big Island of Hawaii, and published two papers analyzing the enhanced weathering process.

Matzner recruited Montserrat for his project after reading his report.

“It’s buying time,” Montserrat said. “You need to cut carbon emissions, but every year we don’t cut emissions it becomes more clear that we need to find a way to remove CO2.”

If the project moves forward, Project Vesta would be the first in North America to use ocean waves to weather volcanic rocks, but it isn’t the first organization to study how rock sequesters carbon.

The idea was mentioned in the 2016 Paris climate agreement, a pledge by nearly 200 nations to cut emissions and prevent global temperatures from rising more than 3.6 degrees F ahrenheit above average preindustrial levels, the point at which warming could begin to have catastrophic consequences. President Trump plans to withdraw the United States from the Paris agreement in 2020.

Studies using crushed volcanic rock on crops have been conducted in the Midwest, Australia, Malaysia and the United Kingdom. In California, UC Davis researchers started field experiments this year with pulverized volcanic rock on 100 acres of alfalfa, corn and almond crops and on rangeland across the Central Valley.

Project leader Ben Houlton, director of the John Muir Institute of the environment at UC Davis, said the study — funded with $5 million from California’s cap-and-trade program — uses a metabasalt taken from the tailings at a local mine and subjects it to the same weathering process as the beach project would, except on land.

Houlton said olivine was ruled out because it would poison the soil with heavy metals. The rock he uses was selected because it has potassium and zinc in it, which is good for crops. It is pulverized and mixed with the topsoil, where microbial activity causes the weathering that allows carbon dioxide to be consumed.

The idea, Houlton said, is to make the process healthful for crops and useful economically — crop yields have gone up 15% to 20% using the material — providing an incentive for sequestering carbon.

Houlton said his models have shown that farmers could capture between 5 and 10 billion tons of CO2 per year — a little less than a third of what is emitted worldwide — if 75% of earth’s croplands were treated this way.

“I think the capacity for a global scale solution is there,” he said, “but there is still a lot of progress to make on the science that is needed to validate this approach.”

The questions are how fast it can be scaled up, how much it would cost and whether scaling up the process would produce more carbon than it would remove. Also, nobody knows what effect leaching metals, like nickel, would have on the marine environment as olivine dissolves.

“In the big-picture sense, we know that the formation of carbonate rocks is one of the main ways that nature provides long-term removal of atmospheric CO2,” said Christopher Field, a climate scientist at the Stanford Woods Institute for the Environment. “One challenge is getting a process that operates in nature on geological time scales (millions of years) to operate much more quickly. The second challenge is getting the acceleration without requiring so much energy input that we dig a hole we can’t get out of.”

Matzner believes olivine beaches could be turned into economic and cultural resources if governments begin using the substance to fix eroded coastlines or replace sand washed away by rising tides.

“That would be a great way to get lots of this sand deployed,” he said, adding that he will be pushing olivine wedding rings and other jewelry in the name of helping Mother Nature. “We want to create a movement.”

Peter Fimrite is a San Francisco Chronicle staff writer. Email: pfimrite@sfchronicle.com Twitter: @pfimrite