An ongoing tour of literature related to astrobiology, hosted by Dr. David Grinspoon, Curator of Astrobiology at the Denver Museum of Nature & Science.
|Dr. David Grinspoon, Curator of Astrobiology at the Denver Museum of Nature & Science. Click image for larger view.
Greetings people of Earth. In this space we will present reviews of current and classic books related to questions about life in the universe, written by colleagues and friends from the field of astrobiology, or the many related fields in the Earth, space and life sciences.
We will cast a wide net, including scholarly and popular books, fiction and nonfiction, books focused directly on astrobiology, as well as those that are more tangentially related to the field, yet help to illuminate the subject in interesting ways. Who knows, maybe we’ll even include an occasional movie, CD or interstellar webcast.
Here, Charley Lineweaver reviews “ Scientists Debate Gaia,” a collection of essays gathered from an American Geophysical Union conference held in 2000. While not overtly about astrobiology, it nonetheless asks important questions about the development of life and the longevity of civilizations in the universe.
Lineweaver is the author of many articles that range from the origin of life on Earth, to galactic habitable zones, to the cosmic microwave background of the universe. He is also an editor of "The Cosmic Microwave Background," published in 1997. Currently he is a Senior Fellow at Australia National University’s Planetary Science Institute.
|Scientists Debate Gaia, published by MIT press.
Can a Biosphere be Selfish?
The Gaian Challenge to Darwinism
A book review by Charles H. Lineweaver
In the mid-60’s, NASA was developing instruments for the Viking spacecraft to detect life on Mars. To assist in this effort, NASA consulted James Lovelock, an iconoclastic British atmospheric chemist. Lovelock wondered: Can the existence of life be recognized from the chemical composition of a planet’s atmosphere? What would the Earth be like now, if life had never evolved on it? Would there be oxygen in the air? Would the surface temperature be hot like Venus or cold like Mars?
He concluded that it wasn’t necessary to send a spacecraft to Mars. All you needed was to determine the composition of the martian atmosphere –- if life was there, the atmosphere should be in chemical disequilibrium as it is on Earth. It was later found that the martian atmosphere was in chemical equilibrium, and so he concluded that Mars was dead. (Recent observations, however, have detected low levels of methane on Mars.)
Determining what life is and how to recognize it is the Holy Grail of astrobiology. It is at the heart of the question of how we fit into the universe. To make progress, we need to explore the martian subsurface and analyze the atmospheres of the nearest 100 or 1,000 terrestrial planets. Lovelock’s Gaian chemical equilibrium test for the presence of life is fundamental to these efforts. Both NASA and ESA are putting their astrobiological money into interferometric infrared spectroscopy to look for the traces of chemical disequilibrium in planetary atmospheres as the primary biomarker.
Lovelock thought that terrestrial life didn’t just passively produce chemical disequilibrium. There seemed to be some element of control or regulation. In 1974, Lovelock, with his eukaryotic exosymbiont Lynn Margulis, published “Atmospheric homeostasis by and for the biosphere.” (The words “by” and “for” are the revolutionary teleological prepositions that launched Gaia into a sea of controversy that continues to this day.)
Lovelock expanded on this concept in 1978, publishing a book called Gaia that described how the entire biosphere behaves like a living creature. Gaia resonated with throngs of new age agnostics yearning to breathe free, and the book became a best-seller. Lovelock has since written copiously and articulately on Gaia in books of popular science and in professional literature.
|Charley Lineweaver, Senior Fellow at Australia National University’s Planetary Science Institute.
To separate Gaian science from pop-science, the American Geophysical Union sponsored the 1988 Chapman Conference on Gaia. This meeting resulted in an eclectic and authoritative conference proceedings: “Scientists on Gaia.” A second conference held in 2000 has resulted in a new book, “Scientists Debate Gaia.” It has almost the same title, almost the same editors, and many of the same contributors as its predecessor.
Like its older twin, “Scientists Debate Gaia” is a wonderful book --informative, frustrating and inspirational. It is well-bound (bravo MIT press) and well-refereed (bravo editors). The collection includes a few dozen well-referenced chapters (bravo 54 contributing authors). In it you will find a potpourri of theoretical biologists wrestling with that nasty teleological prepositional phrase “for the biosphere,” some ecological case studies and numerical simulations focusing on “by the biosphere,” along with a smattering of history and philosophy.
Gaian science and astrobiology have very similar programs. Astrobiologists look at the stars and ask “What has life done to the planets out there and how can we recognize it?” Gaian scientists have been looking at the Earth for decades asking “What has terrestrial life done to our planet and how can we recognize it?” Astrobiology and Gaian science share a common working hypothesis: Things are connected, so let’s find the connections and try to put the big picture together.
Despite this, astrobiology and Gaian science often remain separate fields of inquiry. Astrobiology attracts mainly astronomers and biologists, while Gaian science attracts atmospheric chemists, geologists and concerned ecologists. Since Gaian scientists have little or no input from astronomers, their questions are more down to earth. They study the physiology of the Earth’s biosphere and atmosphere – also known as “Earth Systems Science” -- and pay little attention to the origin of life or to other terrestrial planets.
|The thin martian atmosphere is mainly composed of carbon dioxide. Planetary scientists have studied the atmosphere of Mars for any signs of gases that could be generated by life.
In this collection, Gaian scientists address many issues of astrobiological interest (there is even a chapter, “Extraterrestrial Gaias” by Franck et al). For instance, over the past four and a half billion years, the Sun’s luminosity has increased by about 30 percent, but the temperature of the Earth’s surface doesn’t seem to have followed in step. Lovelock and Margulis hypothesized that the biosphere regulates the Earth’s surface temperature. There are two obvious ways to do this: Regulate the albedo and/or regulate the abundances of greenhouse gases in the atmosphere.
Lovelock invented the parable of Daisyworld to demonstrate that the biosphere could regulate the albedo. An interesting and perhaps devastating critique of this regulatory ability is given in Weber and Robinson’s chapter “Daisyworld Homeostasis and the Earth System.” They suggest that Daisyworld’s thermoregulatory properties are due to assumptions of the model rather than some necessarily evolved or emergent phenomenon.
However, as mammals, we are proud of the way our bodies regulate our body temperature to within half a degree of 37 degrees Celsius. Like any ability of a living organism, it evolved from a population that started out with little or no temperature regulation. Members of the population that could regulate out-reproduced the non-regulators. Today we describe this behavior as “self-regulation”—the temperature is maintained “by and for” the benefit of our bodies. A nice Gaian extension of this idea is J. Scott Turner’s analysis (“Gaia, Extended Organisms and Emergent Homeostasis”) of the thermoregulation of termite colonies, presumably by and for the colony. So if a miniature ecosystem can evolve to do it, why can’t a big one?
On the surface, natural selection and Darwinian evolution are simple ideas, but a fundamental debate has been percolating for years: What is the unit of selection? A gene? A chromosome? An individual? A group of individuals of the same species? An ecosystem? Do ecosystems compete with each other? If so, when one ecosystem out-competes the others and comes to dominate the biosphere, can we say that the characteristics that led to its success are the products of evolution? Maybe regulatory mechanisms, which are now global and seem to have no competitors, were once sub-global with competitors.
|A termite mound. Termites are able to thermoregulate their environment and therefore ensure the health of the colony.
Forget the debates with creationists and intelligent designers; the scientific debate about the unit of selection is one of the most important challenges that Darwinism has ever had to face. The chapters of this book pose that challenge by asking, again and again, how could the biosphere evolve to regulate the Earth?
Thus, Gaia does what good scientific ideas are supposed to do. It extends and extrapolates a fundamental theory, like Darwinian evolution, into unfamiliar territory, by scaling it up to larger and larger units of selection – from individuals to groups to ecosystems, up to the entire biosphere.
I once heard Lynn Margulis give a lecture in Spanish to an enthralled Mexican audience. She said, “¿Cómo pueden los genes ser egoístas? Ellos no son uno mismo!” (“How can genes be selfish? They have no self!”). But what in the world is a “self?” Maybe the central debate of this book can be similarly synopsized: How can Gaia be selfish? How can it do anything “for” itself? It has no self! Margulis seems willing to accept a selfhood for Gaia, but not for genes.
Richard Dawkins and George Williams each have the opposite view. They argue that genes or individuals (since genes come in packets called individuals) are the units of selection. They say that the behavior of the biosphere can’t be interpreted as the result of Darwinian selection since there were no other biospheres to compete or cooperate with. For them, a large group of competing individuals differentially reproducing is a requirement of evolution.
Maybe selfhood and purpose just fade away on the largest and smallest scales. Darwinian evolution often assumes a sharp boundary between life and non-life. Yet at the smallest scales (viruses and prions) and at the largest scales (Gaia) the familiar properties of life seem to fade away rather than retain the discrete boundaries we normally observe between the biotic and abiotic.
|James Lovelock proposed the Gaia hypothesis, in which Earth is an organism or system capable of self-regulation.
Tyler Volk’s book “Gaia’s Body” was cited in many chapters, and Volk himself contributed a chapter, “Gaia is Life in a Wasteworld of By-products.” He proposed that the atmosphere is one giant waste dump. Life produces wastes, and these wastes build up and affect the environment. They become intolerable for some forms of life, but then along come new forms of life who take advantage of these waste products. Volk’s point is that poop just happens. Thus the effects of the biosphere’s wastes are certainly “by” but not necessarily “for” the biosphere. Volk made me wonder whether some waste products are fitter than others and whether sewage treatment plants are as important as grocery stores.
Volk’s wasteworld idea is an interesting counter to the teleology of “for the biosphere”. And it solves an objection raised by Dawkins regarding cheaters, because cheaters can’t steal stuff that is being given away for free. But the more I think about wasteworld, the more I’m convinced that all adaptations “for” something start out as by-products. Isn’t our body’s ability to control our body temperature a by-product of evolution --a feature that became a beneficial adaptation (with a maintenance cost) only in hindsight?
Volk suggests using cycling ratios to measure “by and for the biosphere” and to determine how beneficial for life something may be. A cycling ratio is the amount of an element cycling through the Earth and biosphere, divided by the amount that would be cycling through the Earth in the absence of life. Volk estimates the cycling ratio of carbon to be about 200 -- so 200 times more carbon is flowing through the veins of Gaia than would be cycling through an abiotic Earth from plate tectonics and volcanism.
Lenton’s chapter, “Clarifying Gaia: Regulation with or without Natural Selection,” suggests that resistance to change and resilience (or recovery) from change are properties that should be measured to quantify Gaia. There are practical problems with these proposals. The largest is that separating biotic from abiotic processes and their ultimate effects on chemical disequilibrium is complicated, because the boundary between far-from-equilibrium-dissipative-structures and traditional life forms is not sharp.
|A collection of observations by the Earth Observing System flagship Terra were stitched together into a seamless true-color mosaic of every square kilometer (.386 square mile) of our planet.
Image Credit: NASA Goddard Space Flight Center
Two chapters that got me the most excited address thermodynamics and definitions of life. Eric Schneider’s “Gaia: Toward a Thermodynamics of Life” discussed life as part of the universal set of far-from-equilibrium-dissipative-structures. Dorion Sagan and Jessica Hope Whiteside’s “Gradient Reduction Theory: Thermodynamics and the Purpose of Life” discussed the second law of thermodynamics as the purpose of life. Agnostics looking for purpose in their lives would do well to digest this chapter, along with Lovelock’s suggestion that agnostics worship Gaia to fill their religious vacuum. Unfortunately, Sagan and Whiteside’s profound insights and overviews sometimes revert to continental philosophizing. Oh well. There is still grandeur and universality in this thermodynamic view of life. It has the advantage of being so general that it can be applied to life elsewhere in the universe, and at the same time it tells us the purpose of life. Not bad for $50.
I’m enthusiastic about the way the holistic Gaian program, presented so well in “Scientists Debate Gaia,” is opening scientific minds. But as an astronomer I’d like to see Gaian scientists recognize that Gaia is part of a larger whole – that the Earth is not a closed system and that Gaia has a mother. When we begin to wonder whether our Galaxy is a life form called Galactea, do we become so open-minded that our brains fall out? Maybe this will be the subject of the next Gaian conference. Let a thousand flowers bloom, right in the middle of a cow paddy.
“Buy” this book “for” yourself. Scribble next to all the frustrating and inspirational ideas. My copy is thoroughly defaced. It is a must read for any life form that is even pretending to look for extraterrestrial life.
Scientists Debate Gaia: The Next Century, edited by S.H. Schneider, J.R. Miller, E. Crist and P.J. Boston. MIT Press, Cambridge, Massachusetts, 2004.
Dawkins, R. (1982) Extended Phenotype: The Gene As the Unit of Selection, W.H.Freeman & Company.
Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna,M. (2004) Detection of Methane in the Atmosphere of Mars, Science, Vol. 306, 5702, pp. 1758-1761.
Jones, B.W. (2004) Life in the Solar System and Beyond, Praxis, pp 247-252.
Krasnopolsky,V.A.; Maillard, J. P.; Owen,T.C. (2004) Detection of methane in the martian atmosphere: evidence for life? Icarus, Vol 172, Issue 2, p. 537-547.
Lineweaver, C. (2006) “We have not detected extraterrestrial life, or have we?”, in Life As We Know It, ed. J. Seckbach, Vol 10 of series Cellular Origins, Life in Extreme Habitats and Astrobiology, Kluwer, pp 445-457, ISBN 1-4020-4394-5.
Lovelock, J.E. (1978) Gaia: A new look at life on Earth, Oxford Univ. Press.
Lovelock, J.E. (1990) Ages of Gaia: A biography of our living Earth, Bantam.
Lovelock, J.E. (2000) Gaia: the practical science of Planetary Medicine, Oxford Univ. Press.
Lovelock, J.E. (2000) Homage to Gaia: The Life of an Independent Scientist, Diane Pub. Co.
Lovelock, J.E. (2001) “A Way of Life for Agnostics?” Skeptical Inquirer, Sept/Oct, 2001, 25, 5 40-42.
Lovelock, J.E. (2006) The Revenge of Gaia, Allen Lane.
Lovelock, J.E. and Margulis, L.M. (1974), “Atmospheric homeostasis by and for the biosphere: The Gaia hypothesis” Tellus, 26, 2-10.
Sagan, C. & Chyba, C. (1997) “The Faint Early Sun Paradox: Organic Shielding of Ultraviolet-Labile Greenhouse Gases” Science, 276, 1217-1221.
Schneider, S.H. & Boston, P.J. (1991) Scientists on Gaia, MIT Press.
Selsis, F., Despois, D. and Parisot, J.-P., (2002). Signature of life on exoplanets: can Darwin produce false positive detections? Astron. Astrophys. 388, pp. 985–1003.
Volk, T. (1998) Gaia’s Body: Toward a Physiology of Earth, New York:Springer-Verlag
Volk, T. (2002) The Future of Gaia Theory, Climatic Change 52, 423-430.
Watson, A.J. and Lovelock, J.E. (1983) Biological homeostasis of the global environment: The parable of Daisyworld. Tellus, 35B, 284-289.
Williams, G.C. (1966) Adaptation and Natural Selection, Princeton Univ. Press.
Related Web Pages
Read an extended version of this review essay.
From Dr. G’s Bookshelf:This Easter Island Earth
Mars: Goldilocks’ Oasis?
Biosphere Under the Glass
Higher Concepts and Advanced Aliens