Gretchen Fruh-Green of Switzerland’s Institute for Mineralogy and Petrology is the lead author of the Science report. They performed carbon dating of over 30 chimney structures at the Lost City, many of which are no longer active and so have stopped growing. These carbon datings show “many of the sediments sampled to date were deposited just before the last glacial maximum 20,000 years ago”. They estimate that the mantle rocks immediately below the vent are relatively young at 1.5 million years old, but no active volcanic or tectonic process are taking place there today.
As reported by Bob Beale of Australian Broadcasting Corp., the Lost City may serve as a natural laboratory that yields clues into the nature of the Earth’s early ecology, into the origins of life itself and perhaps into the conditions that might foster life on other planets. The team used chemical data to infer the rate at which seawater penetrates to a depth of a few kilometres into the mantle, which is heavily fractured and cracked in that region. When the seawater enters these cracks, it hydrates the rocks to form the mineral serpentine; in doing so, it releases heat that drives the high-temperature venting. The team’s calculations imply that the process has been continuously active for at least 25,000 years – the age of the oldest sediments – and the researchers note that even older vent debris lies beneath them in piles up to 20 m deep. They calculate that the process could keep on producing serpentine and releasing heat for many tens of thousands of years: about 180 cubic km of the massif have already been converted to serpentine.
The Lost City chimneys are mainly made of carbonates, like stalagmites in limestone caves, and range from a clean white colour to grey. Some have been colonised by corals, and microbes are believed to feed off gases such as methane that are released from them. This type of vents may be conducive to life because their fluids are less acidic and are rich in organic compounds, compared to the well-known black-smoker vent systems heated by volcanism, the researchers said. While the Lost City system is the only one of its type known, many others could exist, the researchers say. The fact that hot vents can occur without volcanic activity means they can exist in many more parts of the ocean, increasing the areas where microbial life could have formed.
A Web site has chronicled a recent 32-day expedition to the Lost City that started April 21 using the Atlantis, operated by Woods Hole. It took five days to reach the ocean above Lost City from their base in Barbados where researchers then used the submersible Alvin and an unmanned Autonomous Benthic Explorer. Lost City is nine miles from the nearest spreading center and sits on 1.5 million-year-old crust.