by Lewis Thomas
Berkner has suggested that there were two such explosions of new life, like vast embryological transformations, both dependent on threshold levels of oxygen. The first, at 1 per cent of the present level, shielded out enough ultraviolet radiation to permit cells to move into the surface layers of lakes, rivers, and oceans. This happened around 600 million years ago, at the beginning of the Paleozoic era, and accounts for the sudden abundance of marine fossils of all kinds in the record of this period. The second burst occurred when oxygen rose to 10 per cent of the present level. At this time, around 400 million years ago, there was a sufficient canopy to allow life out of the water and onto the land. From here on it was clear going, with nothing to restrain the variety of life except the limits of biologic inventiveness.
It is another illustration of our fantastic luck that oxygen filters out the very bands of ultraviolet light that are most devastating for nucleic acids and proteins, while allowing full penetration of the visible light needed for photosynthesis. If it had not been for this semipermeability, we could never have come along.
The earth breathes, in a certain sense. Berkner suggests that there may have been cycles of oxygen production and carbon dioxide consumption, depending on relative abundances of plant and animal life, with the ice ages representing periods of apnea. An overwhelming richness of vegetation may have caused the level of oxygen to rise above today’s concentration, with a corresponding depletion of carbon dioxide. Such a drop in carbon dioxide may have impaired the “greenhouse” property of the atmosphere, which holds in the solar heat otherwise lost by radiation from the earth’s surface. The fall in temperature would in turn have shut off much of living, and, in a long sigh, the level of oxygen may have dropped by 90 per cent. Berkner speculates that this is what happened to the great reptiles; their size may have been all right for a richly oxygenated atmosphere, but they had the bad luck to run out of air.
Now we are protected against lethal ultraviolet rays by a narrow rim of ozone, thirty miles out. We are safe, well ventilated, and incubated, provided we can avoid technologies that might fiddle with that ozone, or shift the levels of carbon dioxide. Oxygen is not a major worry for us, unless we let fly with enough nuclear explosives to kill off the green cells in the sea; if we do that, of course, we are in for strangling.
It is hard to feel affection for something as totally impersonal as the atmosphere, and yet there it is, as much a part and product of life as wine or bread. Taken all in all, the sky is a miraculous achievement. It works, and for what it is designed to accomplish it is as infallible as anything in nature. I doubt whether any of us could think of a way to improve on it, beyond maybe shifting a local cloud from here to there on occasion. The word “chance” does not serve to account well for structures of such magnificence. There may have been elements of luck in the emergence of chloroplasts, but once these things were on the scene, the evolution of the sky became absolutely ordained. Chance suggests alternatives, other possibilities, different solutions. This may be true for gills and swim-bladders and forebrains, matters of detail, but not for the sky. There was simply no other way to go.
We should credit it for what it is: for sheer size and perfection of function, it is far and away the grandest product of collaboration in all of nature.
It breathes for us, and it does another thing for our pleasure. Each day, millions of meteorites fall against the outer limits of the membrane and are burned to nothing by the friction. Without this shelter, our surface would long since have become the pounded powder of the moon. Even though our receptors are not sensitive enough to hear it, there is comfort in knowing that the sound is there overhead, like the random noise of rain on the roof at night.
REFERENCE NOTES
THOUGHTS FOR A COUNTDOWN
Hanks, J. H., “Host-Dependent Microbes,” Bacteriological Review, 30:114–35, 1966.
Shilo, M., “Morphological and Physiological Aspects of the Interaction of Bdellovibrio with Host Bacteria,” Current Topics in Microbiology and Immunology, 50:174–204, 1969.
Dilworth, M. J., “The Plant as the Genetic Determinant of Leghaemoglobin Production in the Legume Root Nodule,” Biochemica et Biophysica Acta, 184:432–41, 1969.
Timourian, H., “Symbiotic Emergence of Metazoans,” Nature, 226:283–84, 1970.
Gotto, R. V. Marine Animals: Partnerships and Other Associations. New York: American Elsevier, 1969.
Thompson, T. E., and Bennett, I., “Physalia Nematocysts: Utilized by Mollusks for Defense,” Science, 166:1532–33, 1969.
Theodor, J. L., “The Distinction between ‘Self’ and ‘Non-Self’ in Lower Invertebrates,” Nature, 227:690–692, 1970.
Parker, B. C., “Rain as a Source of Vitamin B12,” Nature, 219:617–18, 1968.
ON SOCIETIES AS ORGANISMS
Ziman, J. M., “Information, Communication, Knowledge,” Nature, 224:318–24, 1969.
A FEAR OF PHEROMONES
Comfort, A., “The Likelihood of Human Pheromones,” Nature, 230:432–33, 1971.
Hoyt, C. P., Osborne, G. O., and Mulcock, A. P., “Production of an Insect Sex Attractant by Symbiotic Bacteria,” Nature, 230: 472–73, 1971.
Wilson, E. O., “Chemical Systems,” in T. A. Seboek, ed., Animal Communication: Techniques of Study and Results of Research. Bloomington: Indiana University Press, 1970.
Todd, J. H., “The Chemical Languages of Fishes,” Scientific American, 224(5):98–108, 1971.
Michael, R. P., Keverne, E. B., and Bonsall, R. W., “Pheromones: Isolation of Male Sex Attractants from a Female Primate,” Science, 172:964–66, 1971.
McClintock, M. K., “Menstrual Synchrony and Suppression,” Nature, 229:244–45, 1971.
“Effects of Sexual Activity on Beard Growth in Man,” Nature, 226:869–70, 1970.
Smith, K., Thompson, G. F., and Koster, H. D., “Sweat in Schizophrenic Patients: Identification of the Odorous Substance,” Science, 166:398–99, 1969.
THE MUSIC OF THIS SPHERE
Howse, P. E., “The Significance of the Sound Produced by the Termite Zootermopsis angusticollis (Hagen),” Animal Behavior, 12:284–300, 1964.
Busnel, R. G., ed., Acoustic Behavior of Animals. Amsterdam: Elsevier, 1963.
Payne, R. S., and McVay, S., “Songs of Humpback Whales,” Science 173:585–97, 1971.
Morowitz, H. J., Energy Flow in Biology: Biological Organization as a Problem in Thermal Physics. New York: Academic Press, 1968.
AN EARNEST PROPOSAL
Margulis, L., The Origin of Eukaryotic Cells. New Haven: Yale University Press, 1970.
VIBES
King, J. E., Becker, R. F., and Markee, J. E., “Studies on Olfactory Discrimination in Dogs,” Animal Behavior, 12:311–15, 1964.
Kalmus, H., “The Discrimination by the Nose of the Dog of Individual Human Odours and in Particular of the Odours of Twins,” Animal Behavior, 3:25–31, 1955.
Regnier, F. E., and Wilson, E. O., “Chemical Communication and ‘Propaganda’ in Slave-Maker Ants,” Science, 172:267–69, 1971.
Moulton, D. G., Celebi, G., and Fink, R. P., “Olfaction in Mammals,” in Wolstenholme, G. E. W., and Knight, J., eds., Taste and Smell. London: J. and A. Churchill, 1970.
Hara, T. J., Ueda, K., and Gorbman, A., “Electroencephalographic Studies of Homing Salmon,” Science, 149:884–85, 1966.
Wiener, H., “External Chemical Messengers,” I: “Emission and Reception in Man,” New York State Journal of Medicine, 66:3153–70; II: “Natural History of Schizophrenia,” ibid., 67:1144–65.
Smith, K., Thompson, G. F., and Koster, H. D., “Sweat in Schizophrenic Patients: Identification of the Odorous Substance,” Science, 166:398–99, 1969.
Margolin, A. S., “The Mantle Response of Diodora aspera,” Animal Behavior, 12:187–94, 1964.
Benacerraf, B., and McDevitt, “The Histocompatibility-Linked Immune Response Genes,” Science, 175:273–78, 1972.
Whittaker, R. H., and Feeny, P. P., “Allelochemics: Chemical Interactions Between Species,” Science, 171:757–70, 1971.
ANTAEUS IN MANHATTAN
Watson, J. A. L., Nel, J. J. C., and Hewitt, P. H., “Behavioural Changes in Founding Pairs of the Termite Hodotermes mossambicus,” Journal of Insect Physiology, 18:373–87, 1972.
Wheeler, W. M., Essays in Philosophical Biology. Cambridge, Mass.: Harvard University Press, 1939.
Larousse Encyclopedia of Animal Life. New York: McGraw Hill, 1972.
THE IKS
Turnbull, C. M., The Mountain People. New York: Simon and Schuster, 1972.
SOME BIOMYTHOLOGY
Gressitt, J. L., Samuelson, G. A., and Vitt, D. H., “Moss Growing on Living Papuan Moss-Forest Weevils,” Nature, 217:765, 1968.
Margulis, L., “Symbiosis and Evolution,” Scientific American, 225(2): 48–57, 1971.
Giese, A. C., Blepharisma: The Biology of a Light-Sensitive Protozoan. Stanford, Calif.: Stanford University Press, 1973.
ON VARIOUS WORDS
Wheeler, W. M. “The Ant-colony as an organism,” Journal of Morphology, 22:307–25, 1911.
Maeterlinck, M., The Life of the White Ant. London: Allen and Unwin, 1930.
Marais, E. N., Die Siel van die Mier. Pretoria: J. L. van Schaik, 1933.
Lewis, C. S., Studies in Words. Cambridge: Cambridge University Press, 1960.
Morrison, P. “All That Is Made,” Bulletin of the American Academy of Arts and Sciences, 25(5):7–19, 1972.
Julian of Norwich, Revelation V, 1373.
LIVING LANGUAGE
Grassé, P. P., “Nouvelles Expériences sur le termite de Muller et considerations sur la théorie de la stigmergie,” Insectes Sociaux, 14: 73–102, 1967.
Wilson, E. O., The Insect Societies. Cambridge, Mass.: Harvard University Press, 1971.
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