Now, more than 40 years later, we're ready to start deep-sea mining for real. We're depleting many of our land-based stores of minerals, and remote though it is, the bottom of the ocean is a likelier source of precious minerals than asteroids. It is strewn with deposits rich in gold, copper, manganese, cobalt, and other resources that supply our electronics, green technology, and other vital tools like medical imaging machines.

In 2019, Canadian mining firm Nautilus Minerals will send robots to excavate deposits rich in copper and gold within the jurisdiction of Papua New Guinea. Other nations are hot on their heels. The International Seabed Authority, which regulates deep-sea mining in international waters, has granted contracts to more than 25 countries to explore for minerals.