From the grounds of a gas-fired power plant on the eastern shores of Canada, a little-known company is pumping a slurry of minerals into the ocean in the name of stopping climate change.

Whether it’s pollution or a silver bullet that will save the planet may depend on whom you ask.

From shore, a pipe releases a mixture of water and magnesium oxide—a powdery white mineral used in everything from construction to heartburn pills that Planetary Technologies, based in Nova Scotia, is betting will absorb more planet-warming gases into the sea.

“Restore the climate. Heal the ocean,” reads the motto stamped on a shipping container nearby.

Planetary is part of a growing industry racing to engineer a solution to global warming using the absorbent power of the oceans. It is backed by $1 million from Elon Musk’s foundation and competing for a prize of $50 million more.

Dozens of other companies and academic groups are pitching the same theory: that sinking rocks, nutrients, crop waste or seaweed in the ocean could lock away climate-warming carbon dioxide for centuries or more. Nearly 50 field trials have taken place in the past four years, with startups raising hundreds of millions in early funds.

But the field remains rife with debate over the consequences for the oceans if the strategies are deployed at large scale, and over the exact benefits for the climate. Critics say the efforts are moving too quickly and with too few guardrails.

Planetary, like most of the ocean startups, is financing its work by selling carbon credits—or tokens representing one metric ton of carbon dioxide removed from the air. Largely unregulated and widely debated, carbon credits have become popular this century as a way for companies to purchase offsets rather than reduce emissions themselves. Most credits are priced at several hundred dollars apiece.

The industry sold more than 340,000 marine carbon credits last year, up from just 2,000 credits four years ago, according to the tracking site CDR.fyi. But that amount of carbon removal is a tiny fraction of what scientists say will be required to keep the planet livable for centuries to come.

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