Follow the Water…to Life?
Astrobiology, the search for life beyond Earth, is the fastest growing scientific discipline, at least in terms of increased government funding.
However, despite a quadrupling of funds in just six years (compared to a vastly smaller increase for all the other sciences) and despite decades of diligent searching, no one has found any evidence for life beyond planet Earth. Yet scientists in the astrobiology community and the politicians who fund them remain convinced that life will inevitably be found.
In their search for extraterrestrial life astrobiologists employ the mantra, “Follow the water.” They (wrongly) extrapolate from what they observe on Earth that wherever liquid water exists, life must exist. They also (rightly) recognize that without liquid water physical life is impossible.
Given the necessity of water for life, a recent scientific meeting convened to question whether the notion of water-freelife is feasible.1 While the assembled scientists could not give an absolutely definitive negative answer (science never can), they did conclude that no simple molecule exists that mimics all the useful (essential) biological functions of water. In addition to noting water’s profoundly anomalous features that make life chemistry possible, they discovered and reported two new design features in water’s effect on proteins.
The life-critical role of water molecules on or near the surfaces of proteins has been acknowledged for decades. New, however, is the discovery that water molecules within the internal structure of several proteins preserve the conformation (shape and structural strength) of those proteins. The scientists at the meeting also noted a second design feature: only water allows proteins to achieve optimal stability for their critical-to-life functions. Too much stability means that proteins will not fold or unfold properly. Too little stability means that proteins, once folded, will not adequately maintain their folded structure. Chemists now recognize in water a narrow chemical habitable zone, which adds more stringent parameters for life.
Water seems a miraculously designed molecule. However, the mere existence of water does not guarantee a natural origin (or ongoing existence) of life. Astrophysicist Paul Davies exposes this “ingredients fallacy.”2 Many biologists and astronomers argue that because the ingredients of life-hydrogen, carbon, nitrogen, oxygen, sulfur, water, and hydrogen cyanide-are ubiquitous and abundant in the universe, so too life must be widespread in the universe. Davies demonstrates that this argument is akin to saying that since silicon is ubiquitous and abundant in the universe (it is the seventh most abundant element), then laptop computers-made partly of silicon but far less complex than life-must be widespread in the universe. Likewise, he points out that whereas on Earth “life invades niches with liquid water, it does not emerge there de novo.” He concludes that “the mere existence of liquid water does little to raise expectations that life will actually be found.”
Liquid water is just one of hundreds of different physical and chemical ingredients necessary for life’s existence-but none of these, either individually or together explain life’s origin. A list of essential characteristics can be found on the Reasons To Believe Web site (www.reasons.org). A calculation based on just 202 characteristics conservatively puts the possibility of finding an extraterrestrial site for the existence of life anywhere in the observable universe, independent of divine intervention, at less than one chance in 10217. This number is so huge that the total number of protons and neutrons in the universe (1079) is infinitesimal by comparison.
If scientists indeed follow the “miracle molecule,” water, to find life, it will surely lead to the Miracle Worker, revealed in the pages of the Bible.
- Philip Ball, “Water, Water, Everywhere?” Nature 427 (2004): 19-20.
- Paul C. W. Davies, “How Bio-Friendly Is the Universe?” International Journal of Astrobiology 2 (2003): 115-20.