HALIFAX, Nova Scotia — 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 start-ups 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.

“It’s like the Wild West. Everybody is on the bandwagon, everybody wants to do something,” said Adina Paytan, who teaches earth and ocean science at the University of California, Santa Cruz.

Planetary, like most of the ocean start-ups, is financing its work by selling carbon credits — or tokens representing one metric ton of carbon dioxide removed from the air.

Largely unregulated, 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 each.

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.

Those leading the efforts, including Will Burt, Planetary’s chief ocean scientist, acknowledge they’re entering uncharted territory — but say the bigger danger for the planet and the oceans is not moving quickly enough.

“We need to understand if it’s going to work or not,” he said. “The faster we do, the better.”

‘Like a vacuum’

Most companies looking offshore for climate solutions are trying to reduce or transform the carbon dioxide stored in the ocean. If they can achieve that, Burt said, the oceans will act “like a vacuum” to absorb more gases from the air.

Planetary is using magnesium oxide to create that vacuum. When dissolved into seawater, it transforms carbon dioxide from a gas to stable molecules that won’t interact with the atmosphere for thousands of years. Limestone, olivine and other alkaline rocks have the same effect.

Other firms are focused on growing seaweed and algae to capture the gas. These marine organisms act like plants on land, absorbing carbon dioxide from the ocean just as trees do from the air.

The company Gigablue, for instance, has begun pouring nutrients in New Zealand waters to grow tiny organisms known as phytoplankton where they otherwise couldn’t survive.

Others view the deepest parts of the ocean as a place to store organic material that would emit greenhouse gases if left on land.

Halifax Harbour is just one location where Planetary hopes to operate. The company has set up another site at a wastewater treatment plant in coastal Virginia and plans to begin testing in Vancouver later this year.

“The whole point here is to mitigate against a rapidly accelerating climate crisis,” Burt said. “We have to act with safety and integrity, but we also have to act fast.”

Scientists have acknowledged major unknowns. But some of the principles behind the technologies have been studied for decades now, and the laboratory can only simulate so much.

It’s unclear if the U.S. government will stall or support ocean climate work going forward. The policy landscape continues to shift as the Trump administration seeks to roll back environmental regulations and reconsider the scientific finding that greenhouse gases endanger public health.

Though Musk, a White House adviser, has downplayed some of his past statements about global warming, four years ago his foundation committed $100 million to fund a competition for the best solution for carbon capture, of which Planetary is in the running for the top prize.

The winner will be announced April 23 — the day after Earth Day.