30. Extreme Environment: Black Smoker

Another place to look for analogs to martian life is in extreme environments on Earth, environments that might have once existed on Mars. Since Mars once had abundant liquid water (slides #4, #5, and #7) and had many volcanos, it might have had many volcanic hot springs. On Earth, many kinds of simple micro-organisms live in hot springs. Some organisms even need the hot, sulfur-rich water that the springs provide in order to live. This picture shows a common type of volcanic hot spring on Earth, a “black smoker” hot spring along a mid-ocean ridge in the eastern Pacific Ocean. At black smokers, water heated by hot rock underground is injected into the cold sea water of the ocean floor. The hot water is very rich in sulfur and very poor in oxygen; as it hits the ocean water, black sulfur-rich mineral grains form a cloud. This picture of a black smoker was taken from a submarine (the Alvin), just barely visible at the bottom right. The hot spring water has made solid tubes that stick straight up from the sea floor; the “black smoke” is on top of the tube in the center of the picture.

Few animals can live so deep in the ocean — where it is so dark, so hot, and there is so much sulfur. But Methanococcus jannaschii, a single-celled micro-organism, needs these conditions to survive; it grows best at 85°C (185°F), and lives by taking energy from the hot spring water as it mixes with the ice-cold sea water around it. This way of life is very different from the familiar kinds of life — plants that use light and carbon dioxide from the air, or animals that eat plants or other animals. The Methanococcus way of life shows how diverse and robust life can be, and that life can persist in the worst environments Earth has to offer. Perhaps life could also persist and thrive in martian environments. One job in our future studies of Mars is to learn whether hot springs like this one, or hot springs underground, ever existed on Mars.

We are frequently reminded of just how incomplete our understanding remains of life on Earth. In a paper published in Science in August 1996, a group of scientists at the Institute for Genomic Research in Rockville, Maryland, reported that they had decoded the genetic sequence of Methanococcus jannaschii. Its DNA differs substantially from the two main genetic branches of life on Earth, the bacteria and eucaryotic organisms such as humans and plants that have cells with nuclei. Methanococcus is an archaeon, an organism that looks like a bacterium, but works differently inside. This type of micro-organism was believed to have diverged from the bacterium strain as long as three billion years ago. However, new research reveals that Methanococcus jannaschii was genetically very different from bacteria. In the words of the team's leader, J. Craig Venter: “In decoding the genetic structure . . . we were astounded to find that two-thirds of the genes do not look like anything we’ve ever seen in biology before.” Fascinating discoveries like this one serve as a reminder of the limits of our current Earth-based knowledge. As we mount a serious search for life elsewhere in the universe we must be ready to find life in unexpected forms and unpromising places.

Woods Hole Oceanographic Institute

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