IT WAS shortly after midnight on 4 December 2000 when Gretchen Fr眉h-Green, a usually cool-headed Swiss geochemist, came running into my cabin in a state of excitement.
We were several days into a month-long voyage to explore a rugged underwater mountain called the Atlantis Massif, which rises up from the Mid-Atlantic Ridge. She had spotted something that she thought I really ought to see for myself.
During the day, members of the 25-strong international research team would dive down in the submersible 鈥淎lvin鈥� to study the mountain, and at night we dragged a camera behind the boat, projecting images to the ship. It was while Fr眉h-Green was watching those real-time images that she saw odd forms looming near the summit of the mountain. What could they be?
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The obvious candidates were hydrothermal vents 鈥� the underwater hot spring systems that occur along volcanic ridges and teem with life despite the absence of sunlight. They are my speciality, hence the midnight call. The vents we knew about were black smokers, dark mineral towers that belch murky, sulphurous plumes and swarm with red tubeworms and shrimp. But these new ones were snow-white, and at first sight there were few signs of animal life.
The next day felt taut as we planned a dive, and American geologist Jeff Karson and I went down to explore. We knew we only had a few hours of air, and we didn鈥檛 want to waste a minute. It鈥檚 hard going: the submersible is a little over 2 metres across, with three viewports, so it鈥檚 like having three people crammed in the front of a Volkswagen Beetle. The view is narrow, and you can only see what鈥檚 captured in the headlights.
We knew from the video that there were at least two limestone towers, but eventually we found up to 30. The tallest rose for 60 metres 鈥� we called it Poseidon. It was an incredibly peaceful place, like a very old redwood forest whose canopy is too high to see.
We were still excited 鈥� and in awe. We sensed that our discovery might be as important as that of the black smokers in the 1970s. Until then, researchers thought that most life was driven by sunlight and photosynthesis, and that the bottom of the ocean was a desert. Black smokers changed all that by showing that the earliest life could have been fuelled by gases released from underwater volcanoes.
Here we were, confronted by something different again. We now know that the limestone towers are produced when seawater percolates through deep-mantle rocks forced to the surface because of geological fault activity. Rocks and seawater react to produce heat, methane and hydrogen 鈥� a combination that seems able to support a surprising range of micro-organisms.
We named the place the Lost City, because of the Atlantis connection 鈥� and because the chimneys were like Roman or Greek towers. It makes sense, with hindsight, that such places should exist. But nobody had predicted their existence, so our discovery had a major impact. And it changed my thinking: I鈥檓 now convinced that we鈥檒l find similar places, and probably other types of hydrothermal vents.
It鈥檚 the most thrilling thought: the more we look, the more we find the sea-floor is capable of supporting more life than we thought possible, and that life is capable of springing up in the most unexpected places.
