The years 1996-2000 were interesting to the astronomy community for many reasons. Many will remember the pronouncement of Martian fossilized life and the huge groundswell of commentary that the Allan Hills meteorite garnered. And, it was during those years that NASA announced the past presence of water on the Martian surface. Thus it would seem, the two (life and water) would go hand-in-hand. And, I was one of the converts who wanted to believe in the veracity of past life on the red planet. Since that time I have often wondered to myself—why did the ALH84001 finding not hold-up as well as it might? During the time period I recall reading many research reports on the on ALH84001. And as many can attest, all too often a lack of good, scientific judgment may be based upon a pre-conceived belief system that has no scientific foundation. Supporting the galling belief system is the self-perpetuating rationalization: a lifestyle which subconsciously massages egos. Perhaps, it is a sign of professional growth when one can understand that certain patterns of lifestyle can undermine good, scientific judgment. So, I ask, which way to turn?
FOLLOW THE WATER, THE ENERGY, or BOTH?
Simple Corollaries for Life’s Presence and Evolution . . . Why?
- Life requires a solvent—but it may not always be water
- Life requires energy
- Solvation and Energy generally act in a synergistic manner
Our, Earth-like, lives are heavily tilted towards water and the simpler elements on the periodic table. One primary reason is the energetics, and the meaning of the supposition might be summarized in the following manner—our habitable zone is synergistically shaped between ourselves and the environment in which we live. Try to imagine (for the moment) if our (?) Sun was an F class star and not G class. A primary difference is the temperature of the new Sun—one could surmise that the chemistry would be different, as well. And, quite possibly, silicon-based life may arise—using the carbon analogy of periodicity within the table of elements. (Although the presumption sounds deceptively simple, the chemistry is far from simplistic. See the following link for a podcast for a consideration on weird chemistry–Limits of Organic Life.)
It might, well, be speculated that water could serve the role that oxygen serves in our current milieu—and even metal back-bonding would replace the ubiquitous hydrogen-bond. Although the above-mentioned scenario seems fantastic—one may take into account that there may not be one good, realistic definition for non-carbon life. Thus, as current paradigms of carbon-based biochemistry seem to limit our vision of life—the need to expand efforts in basic research in inorganic models utilizing realistic energy cycles could open new venues for biochemical research.
Some references of note:
Lilia Montoya, Lourdes B. Celis, Elías Razo-Flores, Ángel G. Alpuche-Solís. 2012. Distribution of CO2 fixation and acetatemineralization pathways in microorganisms from extremophilic anaerobic biotopes. Extremophiles 16:6, 805-817.
Charles H. Lineweaver, Aditya Chopra. 2012. The Habitability of Our Earth and Other Earths: Astrophysical, Geochemical,Geophysical, and Biological Limits on Planet Habitability. Annual Review of Earth and Planetary Sciences 40:1, 597-623.
C. S. Cockell. 2011. Life in the lithosphere, kinetics and the prospects for life elsewhere. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369:1936, 516-537.
Jorge Rodríguez, Juan M. Lema, Robbert Kleerebezem. 2008. Energy-based models for environmental biotechnology. Trends in Biotechnology 26:7, 366-374.
Niles Lehman. 2008. A Recombination-Based Model for the Origin and Early Evolution of Genetic Information. Chemistry & Biodiversity 5:9, 1707.