Hydrothermal vents have been around since the planet was first formed. They are a natural by-product of Plate Tectonics, the process that forms, moves, and eventually consumes entire continents.
The largest geological feature on Earth is one continuous mountain range over 40,000 miles (65,000 km) long, collectively called the Mid-Ocean Ridges. This system encircles the globe like the seam on a baseball, and vents are formed at the points where the continental plates are pulling apart from each other.
Seawater is forced into fissures in the ocean floor by the tremendous pressures found about 2300 meters (7500 feet) below the surface where vents are located. That seawater eventually finds its way into the magma of the Earth where it is superheated and then returned to the ocean at temperatures as high as 400o C (750o F).
The black "smoke" you see is actually a cocktail of metals and minerals drawn from deep within the earth which precipitates out and rains down upon the seabed below when it hits the extremely cold water at the bottom of the ocean. The gold deposited on the chimney by the process is clearly visible in the picture above.
The Marshall Hydrothermal Recovery System is the first mention in the patent literature of any utilization of hydrothermal vents for energy, or anything else.
It goes far beyond simply recovering the staggering heat output of the vents. It is also the world's first practical deep-ocean mining system, and it also has the potential of becoming the most energy-efficient water desalination system ever devised.