Living below the sea is possible, at least for a short time. So what is stopping us creating colonies to ease over-population, or guard against disasters?
Ian Koblick hoped the colourful seaweed samples he brought into class would impress.
His marine biology professor at Stanford University commented on their beauty and asked where he had found them.
Ian replied that he had collected them while exploring off the Californian coast using the Aqua-Lung, an early version of today's scuba equipment.
His tutor dismissed his innovative approach. "Diving is for daredevils," she reprimanded.
"If you want to be a real scientist, collect like a scientist."
The year was 1962, and it did not take long for her words to seem antiquated.
Jacques-Yves Cousteau's exploration of shipwrecks, discovery of previously unknown marine flora and fauna, and invention of novel deep-sea exploration tools had already captured public imagination worldwide.
A wave of interest in undersea exploration was washing over the scientific community.
There was serious talk of creating colonies on the bottom of the sea.
As for Koblick, he disregarded his professor's advice and went on to become an ocean explorer and aquanaut.
Ten years later, he opened La Chalupa, then the largest and most advanced underwater habitat and research facility at the world.
Since then, however, interest in sending humans underwater for extended periods of time has ebbed.
Of more than a dozen underwater habitats that once existed, just three remain, all in the Florida Keys.
Koblick and his collaborators own and operate two of them - the Marine Lab, which is used as a research and training base by the likes of the US Navy and Nasa, and the Jules Undersea Lodge, which offers everything from education and training facilities to undersea weddings and luxury romantic getaways at $675 per night.
Creating larger-scale underwater habitation wouldn't only benefit research (or indeed romantic getaways).
Proponents maintain it could help alleviate over-population problems, or guard against the possibility of natural or man-made disasters that render land-based human life impossible.
The question is how feasible this actually is.
Under pressure
According to Koblick, the technology already exists to create underwater colonies supporting up to 100 people - the few bunker-like habitats in operation today providing a blueprint.
"There are no technological hurdles," Koblick says. "If you had the money and the need, you could do it today."
Beyond that number, technological advances would be needed to deal with emergency evacuation systems, and environmental controls of air supply and humidity.
With safety being paramount, operators assure underwater habitats are running smoothly by monitoring life support systems - air composition, temperature and humidity - from the surface.
Above the National Oceanic and Atmospheric Administration's Aquarius Reef Base, the third of the three existing facilities (which accommodates up to six aquanauts at a time), a bright yellow circular disc tethered to the undersea lab 60ft (18m) below collects data from a variety of sensors and sends it to shore via a special wireless internet connection.
Future habitats could use satellites to communicate this important information.
For now, energy independence is still a challenge.
Sustainable future options might include harnessing wave action or placing solar panels on the surface.
Making larger habitats with multiple modules made of steel, glass and special cement used underwater would be simpler than trying to create one giant bubble.
These smaller structures could be added or taken away to create living space for as many people as desired.
Most likely, we wouldn't want to build any deeper than 1,000ft (300m), because the pressures at such depths would require very thick walls and excessive periods of decompression for those returning to the surface.
Koblick and his colleagues did not experience any ill effects from living below the surface for around 60 days, and he thinks stints up to six months would be feasible.
Source: BBC
