Early Life, Page 15: [Previous Page] [Next Page] [Class Home Page] Textbook pages 110 - 118

Where do we start our Search for E.T. Life?

There are a lot of stars, planets and moons in the Galaxy! Despite the chance of over-looking something important, we must try to limit our search to planets and moons most likely to support life. These four fundamental characteristics have been identified:



• Liquid Water
• Presence of certain Biogenic Elements
• Access to Energy for Organisms
• A Stable Environment

Perhaps the most important of these? Liquid Water




Exobiologists consider the search for E.T. life to be equivalent to a search for Liquid Water. What is so special about water?

A) Water serves as a medium in which nutrients and waste can be dissolved and transported, and as a chemical reactant itself.

B) Water exists as a liquid over a large and favorable Temperature Range. At high pressures, it can stay as a liquid (deep hot oceans). Consider other possible exobiological liquids (which are as naturally abundant as water, astronomically speaking):

Liquid Freeze Boil Range NH3 -78 C -33C 45 CH4 -182 -164 18 C2H6 -183 -89 94

Other liquids have a small range, and exist as a liquid only at very low Temperatures. But, chemical reactions favor warmer temperatures: Evolution is 100x slower in liquid NH3, not to mention the chilly temperatures of liquid CH4 and C2H6.