Life in the Dark - Deep Sea Ecosystems

The hydrothermal vents - which are essentially geysers on the sea floor - support exotic chemical-based ecosystems. Some scientists think the vents are modern-day examples of environments where life began on Earth billions of years ago. And the vents might also hold clues to life on other planets.

The thriving communities of life that surround these hydrothermal vents shocked the scientific world when the first vent was discovered in 1977.

Before 1977, scientists believed that all forms of life ultimately depended on the Sun for energy. For all ecosystems then known to exist, plants or photosynthetic microbes constituted the base of the food chain.

In contrast, these vent ecosystems depend on microbes that tap into the chemical energy in the geyser water that billows out from the sea floor -- energy that originates within the Earth itself.

Because they offer an alternative way for life to meet its fundamental need for energy, these vent ecosystems have piqued the interest of astrobiologists - scientists who study the plausibility of life starting elsewhere in the universe.

"It's the only system we know of on Earth where life can thrive in the complete absence of sunlight," said Bob Vrijenhoek, senior scientist at the Monterey Bay Aquarium Research Institute in Moss Landing, California. Vrijenhoek will conduct DNA analysis on the samples gathered by the expedition.

One chore that astrobiologists have struggled with for years is to define the range of conditions (temperature, salinity, irradiation, chemical composition, etc.) in which "life as we know it" could exist. The discovery of hydrothermal vent ecosystems expanded that range.

Images courtesy Woods Hole Oceanographic Institution The Study Area

"It (the life around the vents) was the first discovery of 'life as we don't know it,'" Vrijenhoek said.

Hydrothermal vents form along mid-ocean ridges, in places where the sea floor moves apart very slowly (6 to 18 cm per year) as magma wells up from below. (This is the engine that drives Earth's tectonic plates apart, moving continents and causing volcanic eruptions and earthquakes.) When cold ocean water seeps through cracks in the sea floor to hot spots below, hydrothermal vents belch a mineral-rich broth of scalding water. Sometimes, in very hot vents, the emerging fluid turns black -- creating a "black smoker" -- because dissolved sulphides of metals (iron, copper, and several heavy metals) instantaneously precipitate out of solution when they mix with the cold surrounding seawater.