Life on a Young Planet (41 page)

__________

¹
Recall that a nanometer equals one-millionth of a millimeter, or one-thousandth of a micron. The head of a pin is about 1.5 million nanometers long.

²
The requirement that cells be “free-living” eliminates symbionts or parasites from consideration. Organisms that obtain much of what they need from other cells can jettison many of their genes. I wouldn’t be surprised to learn of parasites smaller than known free-living cells.

Epilogue

The past is autobiographical fiction pretending to be a parliamentary report.

—Julian Barnes
Flaubert’s Parrot

“H
OW DO WE SEIZE THE PAST
?” muses the narrator in
Flaubert’s Parrot.
“We read, we learn, we ask, we remember, we are humble; and then a casual detail shifts everything.” And so it does. In our efforts to decipher Earth’s early biological history, minute details have repeatedly sparked revelation: here an exquisite cyanobacterium in billion-year-old chert, there a drop in the iron retained by ancient soils, and somewhere else a change in the fabric of carbonate minerals precipitated on the ocean floor—the world in a grain of sand if ever there was one. Individual details may seem trifling, but collectively they reveal the epic drama that carries us from Darwin’s warm little pond to his dilemma of Cambrian diversity, now seen in new light. From there, it is but a short hop to fish, to ungainly amphibians waddling across a Paleozoic swamp, to tiny mammals dodging the footfalls of dinosaurs, and to a species that can not only reconstruct its evolutionary past but contemplate similar histories on other worlds.

The early evolution of life, then, is part of
our
story. We are the product of a planetary history more than 4 billion years long, the latest installment of a book whose final chapters have yet to be written. As Hap McSween wrote in
Fanfare for Earth
, “we are stardust” is not just Woodstock bravado; it is literal truth. The carbon in my body was forged in the crucible of an early star, dispersed into space by a supernova, gathered along with dust and rock as our planet took shape, and then cycled repeatedly among air, oceans, and organisms, through cyanobacteria and dinosaurs, perhaps even through Darwin,
before coming to rest, at least for the moment, in a paleontologist’s brain.

But while the story of evolution undoubtedly includes human beings, it is not
about
us. The long history of life helps to explain our presence, but it can be interpreted as a journey toward man only if we strike a particular course through the Tree of Life. Travel another path and life’s history is a gripping saga of cyanobacterial survival, a cautionary tale of trilobitic fall, or the inspirational story of yeasts finding sustenance in rotting fruit. Each of the 10 million or so species alive today is
equally
the product of Earth’s 4-billion-year evolutionary history—myriad forms separated by evolutionary divergence but united in ecological codependence. Whatever the merits of viewing Earth as
our
world, we could not persist without the bacteria and algae, plants and animals. We are evolutionary latecomers, among the latest threads in an ecological tapestry woven since our planet was young.

It is, in fact, ecology that confers special status on humans, not evolution. Unlike the millions of species that preceded us, humans don’t simply adapt to the environments provided by nature. We take our environment with us, finding comfort in a heated Siberian cabin or an air-conditioned condo in Houston. Armed with technology, our species has spread across the planet, populating it in remarkable numbers. And in the process, we have altered nearly all landscapes, commandeered much of Earth’s photosynthetic production, and come to rival bacteria as participants in biogeochemical cycles. What we do with our special status will determine the plot of the next chapters in Earth’s history, not just for us but for the biosphere as a whole.

There are, of course, other versions of the tale. And not just the “autobiographical fictions” of other paleontologists who refract the same observations through a different lens of experience. I’m thinking of versions that slip free of the factual moorings that guide and constrain my telling—granting us special status by assertion rather than ecology, while simultaneously rejecting almost everything else argued in this book. How do we think about explanations of Earth and life that dispense with science altogether?

The great creation stories of the Bible, or the Upanishads, or the Aboriginal Dreamtime provided ways of comprehending the universe thousands of years before Copernicus, Newton, Darwin, and Einstein
furnished new explanatory language. As eloquent guides to a
moral
universe, they continue to speak across the generations. Indeed, their power derives from their timelessness—words that inspired an iron age shepherd in the Levant can still move a computer analyst in Detroit. Scientific accounts, in contrast, are bounded in time. Today’s state of the art was incomprehensible yesterday, and it will be out-of-date tomorrow. That these two ways of comprehending should be confused in either form or purpose strikes me as both absurd and unfortunate.

The modern world provides substantial tests for faith and theology—the Holocaust, crib death, and Alzheimer’s disease come readily to mind. In contrast, the reconciliation of traditional truths and science is almost trivially simple, requiring only that God, if present, be great enough to mix immanence into the nascent universe, enabling it to unfold over the eons, obedient to the laws of special relativity, nuclear chemistry, and population genetics. Science’s creation story accounts for process and history, not intent. Accepting its ancient counterparts as parables, then, eliminates conflict. (Saint Augustine said as much in the fourth century.) But we must be clear: there can be no other resolution that involves science.

Creationists commonly target evolutionary biology as science’s boogeyman, but the account of early evolution presented in preceding chapters necessitates that the biblical literalist be catholic in his rejection of scientific understanding. He must reject geology because its confluence of pattern and process cannot be accommodated by a biblical timetable. Physics and chemistry must go, too, because they explain the radioactive decay that dates zircons as millions or billions of years old. And astronomy and astrophysics? Don’t even think about them. Indeed, the biblical literalist, passing Permian brachiopods, Cambrian trilobites, and 1.7-billion-year-old schist as she hikes down the Grand Canyon, can only conclude that the
appearance
of age and order in stratigraphic successions is an elaborate ruse, part of a great cosmic charade set up to trap the unfaithful. What sort of God would do that? One who can be petty and vengeful, who may love His creation but doesn’t trust it. A God, in other words, much like ourselves. In his zeal to know the mind of God, the creationist finds only a mirror.

Of course, scripture insists that God made man in his own image, not the reverse. To a nomad seeking oases in a Mideastern desert or a seamstress laboring in medieval Europe, this may well have been received as a literal commentary on God’s visage. Philosophers from Aquinas to
Descartes saw God reflected in the human mind. But the scientific and technological revolution of the twentieth century suggests a more specific, and perhaps more unsettling, reading. To a remarkable degree, we have come to understand the world we live in and, indeed, to dominate it. Through physics and engineering, we can harness the power of atoms for electricity or mass destruction. Medicine makes lame beggars walk. We can fathom the miracle of birth and the mystery of death, and have the power of life and death over species as well as people. Perhaps we were made in God’s image after all.

In the end, dialogue between religion and science matters not so much because it holds the prospect of consensus on our past, but because we need to agree about our future. At the dawn of the twenty-first century, we stand at a crossroads in Earth history. The technological intelligence that gained ecological hegemony for humans now threatens the products of a planetary lifetime. As a result, our grandchildren may know the rhinoceros only from pictures, the rain forest from parks, and coral reefs from history books. Even as we search for life on Mars, we risk losing it on Earth.

Thoughts such as these are disheartening. But the future needn’t be an evolutionary endgame. There is another possibility. At the intersection of ecological dominance and planetary history lie the makings of an evolutionary ethics. If we can understand the immensity of our evolutionary inheritance, we may be moved to preserve it. If we can acknowledge our unprecedented role as planetary stewards, we may be able to discharge our responsibility with wisdom and with honor. On this issue, at least, faith and science find common ground. I don’t know whether God decreed the passenger pigeon, but if He did, it was not for us to exterminate.

Copernicus and Darwin profoundly altered the human sense of self. We do not live at the center of the universe, and we cannot claim the privileges of special creation. In coming decades, planetary exploration may even show that we are not unique or, at the very least, not alone. But whatever astronomy and evolution may take away, ecology restores. On this planet, at this moment in time, human beings reign. Regardless of who or what penned earlier chapters in the history of life, we will write the next one. Through our actions or inaction, we decide the world that our grandchildren and great grandchildren will know. Let us have the grace and humility to choose well.

Further Reading

Prologue

Whitman, W. 1993. When I heard the learn’d astronomer, p. 340 in
Leaves of Grass
. Reprint of the “Deathbed Edition,” originally published in 1892. Modern Library, New York.

Chapter 1. In the Beginning?

Key References on Kotuikan Geology and Paleontology

Bowring, S. A., J. P. Grotzinger, C. E. Isachsen, A. H. Knoll, S. M. Pelechaty, and P. Kolosov. 1993. Calibrating rates of Early Cambrian evolution.
Science
261: 1293–1298.

Kaufman, A. J., A. H. Knoll, M. A. Semikhatov, J. P. Grotzinger, S. B. Jacobsen, and W. Adams. 1996. Integrated chronostratigraphy of Proterozoic-Cambrian boundary beds in the western Anabar region, northern Siberia.
Geological Magazine
133: 509–533.

Khomentovsky, V. V., and G. A. Karlova. 1993. Biostratigraphy of the Vendian-Cambrian beds and the lower Cambrian boundary in Siberia.
Geological Magazine
130: 29–45.

Rozanov, A. Yu. 1984. The Precambrian/Cambrian boundary in Siberia.
Episodes
7: 20–24.

Selected General References

Barnes, J. 1986.
Staring at the Sun
. Jonathan Cape, London. (Source of my opening quotation; reprinted with permission.)

Conway Morris, S. 1998.
The Crucible of Creation: The Burgess Shale and the Rise of Animals
. Oxford University Press, Oxford. (An individualistic but authoritative account of the Cambrian Explosion.)

Darwin, C. 1859.
On the Origin of Species by Means of Natural Selection
. J. Murray, London. (Often reprinted, Darwin’s masterpiece is the foundation of modern biology.)

Fortey, R. 1996.
Life: A Natural History of the First Four Billion Years of Life on Earth
. Alfred Knopf, New York. (A good introduction to paleontology and paleontologists, with much to say about early animal evolution.)

Gould, S. J., and N. Eldredge. 1993. Punctuated equilibrium comes of age.
Nature
366: 223–227. (Commentary on the idea of punctuated equilibrium and the relationship of stratigraphic pattern to evolutionary process.)

Chapter 2. The Tree of Life

Bult, C. L., and 40 others. 1996. Complete genome sequence of the methanogenic archaeon
Methanococcus janaschii
.
Science
273: 1058–1073. (Among the first microbial genomes to be published, this paper established beyond doubt the distinctive nature of archaeal biology.)

Doolittle, W. F. 1994. Tempo, mode, the progenote, and the universal ancestor.
Proceedings of the National Academy of Sciences, USA
91: 6721–6728. (A lively review of efforts by molecular biologists to root of the Tree of Life using duplicated genes.)

Doolittle, W. F. 2000. Uprooting the Tree of Life.
Scientific American
282 (2): 90–95. (A discussion of gene trees, organismsic phylogeny, and the differences between them in evolutionary investigations of microorganisms.)

Fitz-Gibbon, S. T., and C. H. House. 1999. Whole genome-based phylogenetic analysis of free-living microorganisms.
Nucleic Acids Research
27: 4218–4222. (Presents a phylogeny based on whole-genome analysis that compares closely with trees based on ribosomal RNA sequences.)