Researchers have found rare metal deep beneath the surface of the sea—but the discovery largely serves to highlight a pressing dilemma about where we should draw the line when it comes to extracting nature's resources.

The BBC reports that scientists have identified an undersea mountain 300 miles from the coast of the Canary Islands that’s incredibly rich in the rare earth metal tellurium. About 1,000 meters beneath the surface, the mountain’s outer crust is coated in two inches of rock that contains 50,000 times more of the metal than deposits found on land.

What makes the finding so tantalizing is that tellurium is used in some of the world’s most efficient solar cells—but is also, like many rare earth metals, relatively difficult to come by. In fact, Bram Murton, who led the project that uncovered the deposits, has calculated that the mountain could yield 2,670 metric tons of tellurium—equivalent to one-12th of the world's total supply.

It’s not the first time that submarine resources have proven tempting. We know that all kinds of metals exist in rocks at the bottom of the ocean, and some organizations have already expressed interest in extracting them. Canadian firm Nautilus Minerals faced government resistance initially, but is now on course to start mining for copper and gold off the coast of Papua Guinea in 2019. And China is enthusiastically researching how to excavate metals from beneath the Indian Ocean, though it’s yet to start the process in earnest.

The idea of tapping the seabed in this way is obviously attractive. Our insatiable thirst for gadgets, electric cars, and clean power has created huge demand for rare and precious metals that are currently mined—often unethically, sometimes at great expense—here on land. Scraping up the requisite materials from the deep blue would provide a way to ensure that the demands of the future are met, and it’s easy enough to see that pioneers of the approach could also make their millions in the process.

But there’s a big "but": many researchers are concerned about the damage that will be caused by these kinds of initiatives. Earlier this year, for instance, an analysis of deep-sea mining tests showed that even small trials can damage marine ecosystems. The worry is that larger operations will cause far more damage, and it’s unclear what the wider ramifications might be if ecosystems are disturbed. It's not unfeasible that we might we even disturb the way that the seas drive weather patterns or sequester carbon.

But the tellurium find raises a troubling dilemma. Here are the resources required to create a significant quantity of green energy, and yet extricating them could be hugely harmful to the environment. The open question: does the benefit of the former outweigh the potential fallout of the latter? Answering that may not be straightforward, but it would get us further toward understanding whether we’re really ready to mine the depths for all they're worth.

(Read more: BBC, PLoS One, “The Rare-Earth Crisis,” “The Human Cost of the Lithium Battery Revolution”)