The latest scheme to suck CO2 from the air is to capture it in superheated rocks

Can the solution to providing low-cost direct air capture of the greenhouse gas emissions that are causing climate change be found in superhot rocks?

That's what the investors backing the San Francisco-based startup, Heirloom Carbon are betting on. They've poured about $53 million into the company to fund the expansion of its business that superheats limestone to release carbon dioxide that's then captured and use the leftover minerals to capture MORE carbon dioxide from the air.

Limestone is one of the world's most abundant rocks, and by releasing the CO2 that's already trapped inside the formations (and capturing that CO2) Heirloom's backers and founders think they've found a good, relatively cheap solution to take more greenhouse gases out of the atmosphere.

The Bill Gates-backed firm Breakthrough Energy Ventures is a fan. So is Salesforce founder Marc Benioff's investment firm Time Ventures. Alexis Ohanian, the founder of Reddit, is another investor through his investment firm, 776, and so is famous Uber backer Chris Sacca's Lowercarbon Capital (folks, where's the love?).

There are so many high-powered, family offices and tech forward corporate funds involved in this deal that it's almost impossible to list them all. These are folks like The Microsoft Climate Innovation Fund, Ahren Innovation Capital, Carbon Direct Capital Management, and Breyer Capital -- founded by Facebook investor Jim Breyer.

The accelerated carbon mineralization process that Heirloom has developed also raised some initial money from the government through its ARPA-e program (that's the energy program modeled after the deep tech funding which gave the seed money for the internet) and the National Science Foundation.

In the year since it's launched, companies like Stripe, Shopify, Klarna and (one can only assume) Microsoft, have signed up to offset emissions using the company's technology.

Heirloom touts its tech as having the lowest peer-reviewed cost of any direct air process in the world (at the gigaton scale). And, like the company notes in its press release, the world needs to remove tens of billions of tons of CO2 from the atmosphere to keep global temperatures from rising by 1.5 degrees Celsius (even that increase in temperatures is going to cause serious stresses to people around the globe).

"The costs of Direct Air Capture have to come way down to make a meaningful impact on climate change," said Shashank Samala, Co-founder and CEO at Heirloom, in a statement. "Utilizing low cost, earth abundant minerals as a sponge for CO2 is key to making the economics work. In the 10 months since we launched, we've made a breakthrough in the rate we take up CO2 from the atmosphere, giving us a clear path to ultra-low cost, highly scalable carbon removal, and achieving our mission to help reverse climate change."

Heirloom is in the very earliest stages of testing its process and companies like Stripe are paying lots and lots of money for their technology at the moment. An article in Bloomberg put the cost of Stripe's offset purchase at around $2000.

The new money from investors will be used to drive that cost down. Ultimately, Heirloom hopes it can start selling offsets for as little as $50 per ton.

That would be a huge improvement over current costs. The most advanced direct air systems from companies like Carbon Engineering and Climeworks are in the $600 per ton range for carbon removal.

Carbon Engineering is powering the carbon removal operations of 1PointFive, a subsidiary of Occidental Petroleum, which just signed a big offset agreement with the airplane manufacturer, Airbus.

"To limit the planet's warming to 1.5°C, we need to combine significant carbon reductions with carbon removal from the atmosphere. Our catalytic investments in durable direct air capture technologies like Heirloom aim to drive mainstream adoption by bringing down the green premium through large-scale deployment," says Mark Kroese, General Manager, Sustainability Solutions at Microsoft.