Pineapples in Newport, Rhode Island, symbolize welcome and hospitality, a tradition dating back to returning sea captains.

Large swathes of the deep-sea floor contain nodules of the critical minerals cobalt, copper, manganese and nickel. "This is an exciting opportunity for the U.S.," Gerard Baron, ...

The sampling method is pretty standard, he said. Scientists measure the amount of oxygen that is lost, or declines, during a 48-hour period as the chamber sits in place on the ocean floor.

In the 1960s, the U.S. Navy was exploring the other "final frontier" -- the sea. A series of underwater habitats called "Sealabs" were constructed for scientific exploration on the ocean floor.

President Trump signed an order Thursday aimed at making it easier for companies to mine the ocean floor. Scientists and environmental groups say it could harm a fragile ecosystem.