ICY SCIENCE: SCIENCE SPACE ASTRONOMY Spring 2014 | Page 32

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salty - there are lots of ions from minerals dissolved in them. So much of the geology on Earth is from
rock being changed by the way water affects it, but usually this happens slowly, too slowly for anyone to
sit there and watch it happen. But there are a few more dramatic reactions that literally can be watched,
at the hydrothermal (hot water) vent sites. Some of these vents, called black or white smokers, are in
volcanic areas where water seeps down through cracks in the crust, gets super-heated, and boils up in
jets. Black and white smoker vent areas are filled with life, very alien-seeming life. Most of the known
deep-sea vents are so hot and acidic, with temperatures in the vent water up to around 300 degrees C,
that the creatures making a living there are very specialized to deal with those conditions. In some parts
of the vent system, oxygen is extremely low, too low for oxygen-using creatures to live. And most of the
life in these communities depend on the basic energy not of sunlight, but of the chemicals in rocks, captured by microbes.

Normally, when thinking about life that may be elsewhere in the solar system, astrobiologists wouldn’t
use such alien-seeming Earth creatures . The prudent thing is to speculate on living systems that are
well-known. Almost all of the life that we know of on Earth are part of a global food web that is based
on the energy of sunshine, captured by plants, and an energy cycle that uses free oxygen released from
the plants, and so photosynthesis is the energy process that most biologists know best. But Earth is the
only place in the entire solar system where we have found liquid water on the surface, where plants
can reach sunlight. There really doesn’t seem to be any other place in our solar system where we could
expect a food web to be based on plants, or their exhaled oxygen. But what about those worlds with
hidden water? We have to consider life forms that can get their energy from rocks and don’t need free
oxygen to live, and hydrothermal vents are full of them.

ICY SCIENCE | QTR 2 SPRING 2014