Google, Microsoft, others invest $300 million in crushed rocks as CO2 removal solution
Enhanced rock weathering has gone from an interesting idea to large-scale trials in just a few years Read More

A flurry of end-of-year deals has signaled growing excitement around a technology that just a few years ago was considered a newcomer to the suite of methods for removing carbon dioxide from the atmosphere.
The technique, known as enhanced rock weathering (ERW), rests on the idea that slow-moving geochemical reactions between rocks and carbon dioxide can be dramatically accelerated. Microsoft, Google and others have recently invested close to $300 million in startups that believe they can realize that goal and develop carbon credits in the process.
The most widely used ERW approach involves crushing basalt, an abundantly available rock, into a fine powder and spreading it on farmland. Carbon dioxide dissolved in rainwater then reacts with the basalt to deliver a double win: the basalt releases minerals that help fertilize the soil and the carbon dioxide is transformed into bicarbonate, a molecule that remains stables as it washes into oceans and settles as sediment. Scientists estimate that if scaled globally this and related ERW approaches could remove 2 billion to 4 billion tons of carbon dioxide annually.
From rocks to carbon removal

Early movers in carbon removal markets are investing in that potential. Last month, Terradot, a startup testing ERW on farmland in Brazil, announced $58 million in funding from investors and a $27 million purchase of 90,000 tons of removal credits from Frontier, an organization set up by Stripe, Meta and others to provide funding to promising removal technologies. Google, another Frontier founder, participated in the investment round and contracted for an additional 200,000 removal credits. The news came just weeks after ERW startup Heirloom announced a $150 million funding round. Rivals Lithos and Undo also reported recent sales of removal credits to BCG and Microsoft, respectively.
A relatively low price point is one reason for the surge of investments. Credits generated by direct air capture (DAC) facilities, which use fans to blow air over chemicals that absorb CO2 and then pipe the captured gas deep underground, costs in the region of $500 per ton. Frontier’s purchase from Terradot is priced at $300 per ton and the company sees a path to less than $100, said co-founder James Kanoff. Land use is another factor: Unlike DAC facilities, which require industrial-scale plants to be built, ERW can be deployed on existing farmland.
Uncertainties remain
The emerging crop of ERW companies has to prove the potential is real. One fundamental challenge is that ERW generally takes place in open systems. In DAC, it’s relatively simple to know how much CO2 has been captured — the gas can be measured as it flows through the facility’s pipes. Farmland carbon accounting is more complex because CO2 can leave the plot as bicarbonate in water, remain in the soil or be released back to the atmosphere by microbes.
That’s one reason why a review from CarbonPlan, a nonprofit that analyzes climate solutions, noted last year that experimental estimates of ERW’s potential to remove carbon, as measured in tons of CO2 removed per hectare per year, vary by four orders of magnitude. “It’s clear that we are still in the early stages of learning about enhanced weathering,” wrote Tyler Kukla, a research scientist with the organization, and other authors. “As results continue to roll in, we would encourage caution when interpreting carbon removal estimates in the literature.”
Tons of soil
Frontier’s commitment to buy ERW credits now, before the science is fully understood, is designed in part to help Terradot and the other ERW startups it supports to address uncertainties. Kanoff’s team is doing so by drawing what he described as a “crazy density” of samples from the fields it’s treating with basalt. “For one of our recent deployments I think we might have had 10 tons of soil samples,” he said.
The experiments are guided by work done by Cascade Climate, a nonprofit that has developed a methodology for quantifying carbon flows under ERW. In addition to taking soil samples before and after application of basalt, Terradot captures and analyses water that flows from the fields after it rains. It compares those and other measurements to data taken from control plots that were not treated with basalt.
“The question is, can we just take that process that we already know works at this large planetary scale and can we speed it up?” said Kanoff. “That’s the first thing. And then if we can solve that problem and we can speed this thing up to actually remove carbon in years instead of millennia, can we have high confidence in measurement, reporting, and verification of the carbon that’s actually captured?”
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