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Why it matters: Whenever I hear the word “terraforming,” I immediately think of sci-fi novels like Larry Niven’s Ringworld or games like No Man’s Sky, where you can literally dig down or pile up earth to suit your needs. Now, a San Francisco startup is using the concept to save sinking cities and restore wetlands.

San Rafael is sinking into the ocean. The small city just north of San Francisco is already three feet below sea level and is sinking about half an inch per year. The city’s elevation and proximity to the Bay increase its risk of flooding, particularly from rising sea levels.

Other cities in the US and overseas are in similar situations. A Climate Central study estimates that some 300 million people could face routine flooding by 2050. Conventional protection relies on seawalls, which would cost more than $400 billion in the US alone. A new startup is proposing an out-of-the-box approach that could achieve the same goal for a fraction of the cost.

Terranova has developed autonomous robots that inject a slurry of wood waste into the ground. Over time, the process raises the land, reversing subsidence and lowering flood risk.

Terranova claims its technique is more cost-effective and stable than traditional flood mitigation methods.

Terranova co-founder and CEO Laurence Allen said San Rafael’s Canal District sits “really far under sea level.” He estimates a seawall would cost the city $500 million to $900 million, an amount unaffordable for its roughly 60,000 residents. By contrast, the startup estimates it can lift 240 acres of San Rafael by four feet for $92 million.

TechCrunch notes that Terranova recently closed a $7 million seed round, valuing the startup at $25.1 million. Investors include Congruent Ventures, Outlander, GoAhead Ventures, Gothams, and Ponderosa.

The company’s strategy relies on cheap, widely available waste wood mixed with proprietary materials to create a slurry. Tracked robotic units autonomously drill wells and inject the mixture up to 60 feet underground. If kept wet, the wood should not decompose, keeping the terraformed region stable. The startup plans to sell carbon credits to offset project costs.

Terranova developed specialized software for its autonomous robots. Models of the subsurface combine public geographic data and core samples from California water wells. An algorithm calculates injection patterns, which operators can tweak using a SimCity-like interface. Once the robots finish injecting, the slurry consolidates within two hours.

Some experts have raised concerns that underground wood slurry could affect earthquake behavior. However, Allen maintains that similar risks exist with most other alternatives, and his method could be safer and more stable than seawalls or dikes.

Terranova’s business model splits revenue with contractors, but the startup hopes its lower costs will make its approach attractive for projects beyond cities, including wetland restoration. For Allen, the focus is personal.

“I’m from San Rafael, born and raised,” he said. “I really want to save the city.”