The International Seabed Authority — the United Nations body that regulates the world’s ocean floor — is preparing to resume negotiations that could open the international seabed for mining, including for materials critical for the green energy transition.

Years long negotiations are reaching a critical point where the authority will soon need to begin accepting mining permit applications, adding to worries over the potential impacts on sparsely researched marine ecosystems and habitats of the deep sea.

Here’s a look at what deep sea mining is, why some companies and countries are applying for permits to carry it out and why environmental activists are raising concerns.