It almost sounds too good to be true: Take basalt dust that today is wasted in the manufacturing of things like asphalt shingles, sprinkle it on farmers’ fields, and it raises crop yields while also removing carbon dioxide from the atmosphere.
Where’s the catch?
For the entire thing to work, farmers need to add just the right amount of basalt. Too little and they don’t capture much carbon and their crops don’t see any benefits. Too much and the field could end up releasing carbon instead of removing it. Soils are complex systems.
The team at Lithos Carbon thinks they’ve cracked the code. They’re working with farmers in the U.S. Midwest and Southeast, where they’ve already captured over 2,000 tons of carbon this year.
The startup just announced a $6.3 million seed round led by Union Square Ventures and Greylock Partners with participation from Bain Capital Ventures, Carbon Removal Partners, the Carbon Drawdown Initiative, Fall Line Capital and Cavallo Ventures. For Greylock and Bain, it’s their first climate investment.
Lithos’ technique works by speeding up a natural process known as weathering, which captures about 1.1 gigatons of carbon every year. Geologists have been mulling ways to speed the process for a while, and they’ve settled on a few different options, one of which is scattering crushed rocks on fields. Crushing the rock and spreading it out increases its surface area, speeding its ability to remove carbon.
Unlike some other carbon removal technologies, enhanced weathering produces bicarbonate that eventually makes its way to the ocean through rivers and streams, where it may act as a buffer against acidification. There’s no need to find safe and suitable places to inject carbon dioxide.
“We believe that this carbon removal technology has potential to scale up to 10 gigatons of capture a year,” co-founder and CEO Mary Yap told TechCrunch.
One of the current frontrunners is — you guessed it — basalt. Basalt doesn’t remove the most CO2 from the atmosphere compared with other rocks, but it does have other benefits. For one, many sources don’t contain toxic metals, and in agriculture, it can replace lime, or crushed limestone, which many farmers already apply to their fields to reduce the acidification of their soils. Acidic soils are thought to reduce levels of nitrogen, a key plant nutrient. The silicate from the basalt can also help plants resist both pests and drought, and the basalt releases some potassium and phosphorus, both of which act as organic fertilizers.
The farmers who work with Lithos begin by sending in the soil data sheets they have on hand along with acreage, how much lime they apply and when, and a few other parameters. Lithos then runs it all through its software, which tells the company how much basalt should be applied to which field.
“On the farmer side, they get to abstract away all the carbon removal complexity,” Yap said. “We can replace 100% of the agricultural lime that farmers use to de-acidify their fields with the basalt rock dust that we’re providing, and this will at least keep their crop yields the same or improve them. And we’ve seen in our real trials that we get improvements of 5% to 47%.”
The startup currently gets its basalt dust from waste piles at mines. Crushed basalt is widely used in construction, from asphalt shingles to ballast for railroads and aggregate for road construction, but there’s a lower limit on how fine the grains can be. Lithos works with various mines to find sources that are suitable for use in farming, ensuring that the basalt is the right size and doesn’t contain trace metals.
Currently, Lithos applies basalt to farm fields for free, which results in significant savings for the farmers given that lime applications typically cost $40 to $60 per acre (though that number can vary). In exchange, farmers report their crop yields and send soil samples, which the team tests to refine their models. In the future, Lithos may charge for the basalt and its application, but for now, the company makes enough money from carbon removal credits that it’s unnecessary.
Lithos has sold 640 tons of carbon at $500 per ton to Frontier, a consortium of companies including Stripe, Alphabet, Shopify, Meta and McKinsey that makes advanced purchases to encourage carbon removal projects. Yap wouldn’t disclose Lithos’ average cost per metric ton of carbon, but she did say that it currently has “very healthy positive profit margins.”
It’s unlikely that most companies outside of the Frontier consortium would pay that much today or in the near future, so it’ll be important for Lithos to bring down its costs. Transportation of the basalt is a significant contributor, so finding new and appropriate sources close to farm fields will be key. It does seem possible, though, as Yap said Lithos has captured CO2 for as little as $50 per metric ton.
By optimizing how much basalt gets added to fields, Yap said that Lithos speeds the process of carbon removal to the point where the basalt has removed all the carbon it can within two to three years. The company’s models are based on work done by co-founders Noah Planavsky, an associate professor of geochemistry at Yale University, and Chris Reinhard, an associate professor of atmospheric science at Georgia Tech.
Their work also underpins Lithos’ validation tests, which scrutinize farmers’ soils to determine whether the company’s carbon removal claims are living up to expectations. The team has even modeled the effects of farm runoff on their carbon removal rates because that runoff, when it enters waterways, might affect the water’s chemistry, causing it to release some carbon. Lithos also includes transportation and other logistical considerations in its carbon modeling.
“We are trying to be realistic about what the field will need to scale and set ourselves up for a world where there should be honesty in the field,” Yap said.
There’s plenty of funny business happening in carbon markets today, but if Lithos can deliver on its promise to permanently and verifiably remove carbon at the gigaton scale, it might help tip the balance.