The rock dust that could help absorb CO2

For billions of years, rain has slowly dissolved rock and, in doing so, has captured thousands of tons of carbon dioxide from the atmosphere, locking it away as stable minerals. It is one of planet Earth's natural carbon removal systems. Yet, as with many natural processes, it takes a long time – slower than the few years we have to bend the emissions curve. 

Enhanced rock weathering (ERW) replicates this process, speeding it up. Instead of waiting for a mountain to erode grain by grain, crush the rock into dust first, spread it on farmland, and let rain do the rest in years instead of centuries. Is grinding up rock and spreading it on fields really a credible climate solution, or just an appealing idea that doesn't scale? Let's dig into it in this new episode of Green Tech Decoded.

Series

Green Tech Decoded

From revolutionary wind turbines to futuristic materials, a lot is happening in green tech. But what are all these technologies about? And why should we care? In Green Tech Decoded, we explain how these innovations work and why they could redefine our society.

View series

How does enhanced rock weathering work?

As rain falls through the atmosphere, it absorbs CO_2, forming a weak carbonic acid. When that slightly acidic rainwater reaches certain rocks — particularly silicate rocks like basalt — it reacts with them. As a result, it produces dissolved bicarbonate and, eventually, stable carbonate minerals that can lock carbon away for thousands to millions of years.

Enhanced rock weathering accelerates this by increasing the rock's surface area. Grinding basalt with the huge grinders placed in quarries into a fine dust exposes vastly more surface to rainwater than a boulder ever would. Therefore, reactions that would naturally take millennia instead happen over a period of years. The dust is spread on farmland, much like farmers have spread crushed limestone on fields for generations to correct soil acidity. ERW just uses a different rock, chosen for how efficiently it captures carbon rather than for its effect on pH alone.

Basalt is the go-to material: it's abundant, and it's often a byproduct of quarrying operations that would otherwise sit unused. Some developers use faster-reacting minerals like olivine or wollastonite instead, trading lower abundance for a quicker carbon payoff.

What are the pros of enhanced rock weathering?

• It doubles as free fertilizer. Spreading basalt on acidic farmland reduces soil acidity and releases phosphorus and potassium as it breaks down — nutrients crops need and that farmers would otherwise buy as fertilizer. Field trials have found measurably higher crop yields and improved soil health in the first year after application, which gives farmers a reason to participate even before carbon credits enter the picture.
• It reuses existing infrastructure. ERW leans on existing mining and agricultural supply chains — quarries that already crush rock, trucks that already move it, and fields that are already being farmed. That's very different from carbon removal approaches that need entirely new industrial plants built from scratch.
• The carbon storage is durable. Once CO₂ is locked into a solid carbonate mineral or dissolved as stable bicarbonate, which eventually reaches the ocean, it remains there for thousands to millions of years. It is a genuinely permanent removal, unlike carbon stored in a forest, which can burn down. 
• The theoretical scale is enormous. Estimates of how much CO₂ ERW could remove globally vary widely. However, even conservative modelling puts it at several hundred million tonnes of carbon dioxide per year by 2050 – 0.7–1.1 gigatonnes per year by 2100, roughly what Japan emits in a year.  

What are the cons of enhanced rock weathering?

• Mining and transport need to be taken into account. Crushing rock and trucking it to farms takes energy, and that energy usually comes from fossil fuels somewhere in the chain. If the mining, grinding, and hauling aren't done efficiently — ideally using rock quarried close to where it's applied — a meaningful chunk of the captured carbon is offset by the emissions used to capture it.
• We don’t have real-world proof yet.  Because ERW happens underground and over years, proving exactly how much carbon has been removed at any given field is hard. Several measurement standards exist, but other major registries remain on hold pending further scientific development. Most of the eye-catching gigatonne-scale numbers come from lab experiments and computer models rather than large, long-running field trials. Independent researchers, including Project Drawdown, classify ERW as promising but not yet ready for large-scale deployment — worth "keeping watch on" rather than scaling immediately.
• Results vary a lot by geography. Weathering happens fastest in warm, wet, tropical conditions — a farm in Zambia will sequester carbon much faster than an equivalent field in a cooler, drier climate. That means ERW isn't a one-size-fits-all solution, and its economics vary widely from region to region.

Where does the technology stand now?

ERW has moved well past the academic-curiosity stage. Verified carbon credits are now being issued and sold to real corporate buyers, including major tech companies, and the sector is consolidating. 

Lithos Carbon, a US company founded by Yale geochemists, applies basalt to farms across the Corn Belt and has become one of the most visible names in the space. In late 2025, it delivered the largest single ERW carbon-credit issuance ever registered, and it has raised over $60 million in funding to date.

Terradot has emerged as one of the sector's consolidators. In February, it acquired Eion, a company known for deploying ERW across the US Mid-Atlantic and Kenya, and for a "soil fingerprinting" method that tracks trace elements such as magnesium and nickel to verify how much carbon has actually been removed. Eion had already secured offtake agreements with Microsoft, Google, Shopify, and the carbon-removal buyers' coalition Frontier. 

What to expect from enhanced rock weathering?

ERW's appeal is that it doesn't require inventing anything new; it repurposes mining infrastructure and adds up to agriculture. That's also its limit: growth depends on measurement systems catching up, and on carbon markets staying willing to pay for tonnes that are hard to see. 

You'll never watch enhanced rock weathering happen — it works quietly under a cornfield. But if the numbers hold up, it could become one of the more unglamorous, dependable tools in the climate toolkit: spread the rock, and let the rain do the rest.