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July 17, 2006
Part IX: Astrobiology
Extremophiles and the Physical Limits
of Life on Earth... and Mars
Lynn J. Rothschild,
NASA Ames Research Center
38 min. (slideshow requires QCShow Player)
Audio only (mp3 format)
View as a webpage (quicktime, real player) (notes)
Where there are no bounds, that is to say in God, perfection is absolutely infinite.
— Gottfried Leibniz, 1646-1716
Lynn Rothschild describes terrestrial life at its environmental extremes. More importantly, she asks, "Is 'extreme' just a relative term, or are there truly physical limits to organic life?"
Rothschild argues that for carbon-based biochemistries, extreme environments are not merely relative to what we ourselves would find comfortable, but that they're real, and these limits can be outlined in physical terms of maximum and minimum qualities: temperatures, pHs and the like.
She also notes that although aerobic metabolisms have great energetic advantages over anerobics, the capacity to tolerate the toxic effects of free oxygen makes us — and all other complex multicellular life on the planet — extremophiles ourselves. We're not the default condition.
Thirty years ago we had a much more certain idea of what life was like on the Earth, but in the intervening period, we've been surprised a number of times. On one hand, we've discovered that life isn't pervasive on this planet. As Chris McKay pointed out in an earlier lecture, there are broad areas on Earth where life simply hasn't been able to make a go of it, and these areas are as dead to life as the Moon. On the other hand, we've also found life clustered on deep-sea vents at the bottom of ocean and in the boiling acidic waters of hot springs, places we never previously suspected life might exist.
After fifty years of study, astrobiology remains an area of investigation without a known subject. As George Gaylord Simpson wrote in 1964: "this 'science' has yet to demonstrate that its subject matter exists!" That said, astrobiology nevertheless is already serving a valuable purpose. It's causing us to ask, "What are the fundamental natures of life, and where might we find it?", questions we didn't ask before.
We only have one example of life to study, thus we try to legitimately draw every valid conclusion we can from its range of expressions. But because we only have this one example, we're bound to be surprised when we do find the first examples of other geneses of life, just as we've been surprised by the variety and forms of solar systems we're currently finding around other stars.
Lynn presented this talk at a conference on early Mars at Jackson Hole, WY, near Yellowstone, thus the frequent references to Yellowstone in the talk.
— Wirt Atmar
About the Speaker
Lynn Rothschild received degrees in Biology, Zoology, and Molecular & Cell Biology from Yale, Indiana, and Brown Universities. She has combined a broad background in evolutionary biology and protistology to answer questions of microbial evolution including the use of molecular phylogenetic markers and the origin of chloroplasts.
The objective of her work at NASA Ames is to model Precambrian ecosystems and to predict the effect of global change variables, particularly pCO2 and UV radiation, on ecosystem functioning using field and molecular techniques. Other current projects include studies of phytoplankton blooms, endoevaporitic microbes, and analyses of analogs for life on Mars.
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