html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> sciencewriters hypertext book club: 2005-04-03

30 million years ago

Because we perceive as individuals, each of us feels himself to be the center of the universe. As a species and culture, we are similar: like the proverbial carpenter, who sees everything as a board to be nailed, we see the universe in our own image, as centered around and focused upon ourselves. This may well be an illusion of the sort mentioned by magician Jerry Andrus who was told as a kid that Albany, Oregon was the center of the universe. In fact, eighty percent of life's history was microbial, and humans may be no more central to life, the universe, and everything than Albany, Oregon is to geopolitics and world history! (There are, however, different interpretations.) Remnants of bacteria, with DNA identified by moleular biologists as extremely similar to free-living bacterial DNA, divide as mitochondria within the nucleated cells of people as these lines are read. It may be a blow to our collective ego, but we are not masters of life perched on the final rung of an evolutionary ladder. Ours is a permutation of the biosphere, and the cosmos generally. We did not invent genetic engineering, we insinuated ourselves into the life cycles of bacteria, which have been directly trading and copying genes on their own for billions of years. We did not invent agriculture or locomotion on horseback, but became involved in the life cycles of plants and animals, whose numbers have increased with ours. We are probably descended from mothers such as Lucy, whose name comes from the Beatles' song, Lucy in the Sky with Diamonds, which was playing at the archeological dig during the time of her discovery. Lucy was a north African apewoman whose fossil remains date back over three million years. She was an upright walking and running animal but only about three-and-a-half feet tall. If she were crouched on the back of a subway today, you might mistake her for a bag lady.
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    50 mllion years ago

    By 400 million years ago, as the first jawed fishes ambled ashore and at the time of the earliest wingless insects, vascular plants were already thriving. A crucial challenge of the new land environment was water shortage. One solution was the development of seeds. The durable seed permits the plant embryo to wait for the best moment to develop. The invention can be appreciated by conjuring up a comparable structure for mammals. Imagine if human zygotes were wrapped in protective time-release capsules that were activated only by a booming peacetime economy. How convenient it would be for a distracted young woman it she could collect and store her babies-to-be, germinating them only after receiving her college diploma, buying her house and, in general, securing her future. Seeds permitted embryonic plants to wait and silently monitor the environment until favorable conditions arose. The first forests contained giant "seed ferns." These were trees that looked like supersized ferns but which, unlike ferns, produced seeds. For over a hundred million years, from 345 to 225 million years ago, durin g the time of the evolution of winged insects, torpedo-shaped squids, and dinosuars the seed ferns grew in lush, tropical splendor. The first mammals, warm-blooded egg-layers and small marsupials, date to the period of the first flowers, evolving some 125 million years ago. By the early Cenzoic Era, mammals had come into their own, wandering toward polar caps, climbing trees and the highest mountains.
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    70 million years ago

    Although the earliest mammals evolved in the early Mesozoic 200 million years ago they were still in the background 130 million years later during the heyday of dinosaurs. Seventy million years ago was a time of monster reptiles, great forests, and huge chalk cliffs made of microbial shells. For the microbial underlayer of life on Earth did not disappear. Indeed meiotic sex, the kind with two parents contributing an egg and sperm, probably evolved a billion years ago, in the Proterozoic Eon. Animals, plants, and fungi are "late bloomers," only appearing recently on the evolutionary stage. When the bolide (large rock from the sky) hit into the Yucatan area off the Mexico coast sisty-five million years ago, mammals got their chance. We can imagine the gruesome scene. Any herbivorous dinosaurs not killed by shock waves and fire would have slowly starved in the cold dark. Carnivorous ones would have at first dined on their flesh, but they in turn would have died when the meat of the herbivores went rancid. All the while, worms, insects, and other small creatures would have been having their feasts. And on these invertebrates, mammals would have enjoyed a survivor's banquet. Here was the inaugural party, the kicoff event for millions of years of further evolution of mammals. In many places, the recyling of flesh would not have lasted until the light and greenery returned and with it new life. But in some areas it did. That was enough to let mammals emerge into a dinosaur-free world. The brain and body revolution that had allowed our ancestors to steal dinosaur eggs now allowed them to take control over the future. Mammals thus entered evolution's center stage. Nighttime life had given them the ability to regulate their own warmth and be active when nearly every other creature was asleep; more important, it had prepared them in other ways. It had required mothers to feel emotions for their young, their children. Mammals had evolved into devoted parents, not only letting their offspring nestle and huddle into their fur for warmth but also suckling them with mik from their mammary glands (the most primitive mammal, the echidna, does not have teats; its young suck on hairs, which suggests that nursing has its origins in that snuggling up to a mother's warmth). Reptiles had no such care. The emotional attachments of mothers to children in mammals by contrast enabled the rise of other attachments such as friends to friends. Such emotions did much to drive the expansion of the brain. Rising up from reptiles that never dream, mammals had creaed a brain that, after tens of million more years of evolution, could become yours.
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    200 million years ago

    The first mammals evolved while reptiles were taking to the seas and skies. Reptiles strut the stage of life as actors reading the part given them by the sun and the weather. They are ectotherms, which means that they cannot generate heat internally. As a result, their pattern of activity is determined by the sun. We sometimes mistakenly call this cold-bloodedness, but reptiles can be as warm as you. Wheat makes you different is that your body automatically--whatever the weather--accurately keeps much the same temperature. Mammals have hair, sweat glands, insulating fat under the skin, and cells densely packed with power-generating mitochondria. The temperature differs among mammal species (wolves' body temperature is the highest at 105 degrees F while echidnas' is the lowest at 73.7) but these mammalian traits stabilize internal temperature. Inner temperature control was necessary for mammals to roam under cover of the night. In the dark they could not be seen and in the cold reptiles were sluggish. Under cover of the dark mammals could hunt invertebrates and steal eggs from the stronger but stupider rulers of the day, reptiles. The reptiles' inability to control their temperature does not make them less successful than mammals. There may be no polar iguanas or Arctic sea snakes but there are an estimated ten billion lizards in Italy alone. Reptiles have a big advantage: keeping one's blood warm within narrow limits requires eating vast amounts of food. Even at an ideal air temparature, a mouse uses up to thirty times more energy than a similar-sized foraging lizaard. But cold-bloodedness is a dead end for the evolution of intelligence. And here mammals had an edge. That edge became crucial sixty-five million years ago when an asteroid or comet smashed into the Yucatan areal off the Mexico coast. Not only did its impact kick vast amounts of dust into the upper atmosphere, but it started worldwide fires that belched out smoke clouds of Armageddon proportions. As a result, the Earth was lightless for several years, vegetation died, and there were mass extinctions, including the vanishing of the last of the dinosaurs. While living at night could not save those living in the Yucatan peninsula, it did help others. At such a dark moment in the world's history, it paid to be able thrive in the night, in the cold, and to possess an intelligent brain.
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  • Take me to the Late Mesozoic

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    300 million years ago

    In the late Paleozoic Era, less than a third of a billion years ago, microbes were carried ashore in the intestines of roving aimals. As complex as it is compared to an inanimate droplet of chemicals, the bacterial cell is quite a simple affair among life forms. DNA floats unpackaged in bacteria. Cells with nuclei such as ours and those of all animals, by contrast, are studded with mitochondria and plastids, and held together by a network of reticular structures and by the streaming, pulsing cytoplasm around them. The nuclear DNA, much of it repetitive, is coiled tightly into chromosomes wheich are contained in a membrane-bounded nucleus. Genetic evidence fingerprints the origin of nucleated (or "eukaryotic") cells from mixtures of living bacteria. Living corporations (that remained because they were good metabolic fits), some of the mergers began as hostile takeovers of one organism by another. But over hundreds of millions of years they became so interwoven that it took the electron microscope and biochemical analysis to trace the multiple origins of the nucleated cell. Modern kinds of bacteria suggest what happened. Bdellovibrio and Daptobacter are oxygen-using bacteria that break into other bacteria, multiplying inside: these look similar to the ancestors of the oxygen-using bacteria that became the mitochondria. The originally invaded bacterium was a larger being like Thermoplasma, an organism intolerant of concentrated atmospheric oxygen that dwells in hot and acidic waters such as found in Yellowstone National Park. Using a primitive sulfur metabolism, this ancient oxygen-intolerant part of the partnership may date back to the origins of life itself in and around iron sulfide structures. Plants have an even more complicated partnership: their green parts, or chloroplasts, have been traced to free-living bacteria such as Prochloron. The addition of a photosynthetic bacterium to the mix made it unnecessary to actively seek food. This was a further refinement and arguably an advance upon the more frenetic lifestyle that led to animals.
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    500 million years ago

    Some 500 million years ago animals developed hard parts from deposits of cellular waste. Unaware of the global power they were generating, the new oxygen-using bacteira flourished in their local niches all over the planet for hundreds of millions of years. But eventually, as atmospheric oxygen levels rose toward 21 percent, perhaps 2.2 billion years ago, a new kind of cell came on the scene. This was the eukaryotic cell with its key feature, the nucleus and its important secondary characteristic, oxygen-using cell parts known as mitochondria. When eukaryotes live as single cells they are called protists. Amoebae and paramecia are examples of protists. But as primitive as these cells may seem, their basic cell structure is almost identical to that of the multicellular bodies of animals, fungi, and plants. As Stonehill College astronomer Chet Raymo pointed out, the difference between the new cells and the old bacteria in the fossil record looks as drastic as if the Wright Brothers' Kitty Hawk flying machine had been followed a week later by the Concorde jet. But this doesn't mean that something miraculous happened--divine intervention to get from bacteria to fungi! Rather, the genetic evidence is clear: the new cells, the kind that we find in human bodies (and, if you add the green parts called chloroplasts, in plant bodies) came about when different kinds of bacteria merged. In retrospect, this makes sense: the bacteria that were able to detoxify hazardous oxygen were in great demand, and any organism that could team up with them was assured life on the surface rather than death or slinking down into the relative safety of the anoxic muds!
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    700 million years ago

    The oxygen holocaust was a worldwide pollution crisis that occurred about two billion years ago. Before this time there was almost no oxygen in the Earth's atmosphere. The Earth's original biosphere was has different from ours as that of an alien planet. But purple and green photosyntetic microbes, frantic for hydrogen, discovered the ultimate resource, water, and its use led to the ultimate toxic waste, oxygen. All organisms are open thermodynamic systems which necessarily produce waste: our precious oxygen was originally a gaseous poison dumped into the atmosphere. The appearance of oxygen-using photosynthesis and the resulitng oxygen-rich environment tested the ingenuit of microbes, especially those producing oxygen and those nonmobile microorganisms unable to escape the newly abundant and reactive gas by means of motion. The microbes that stayed around responded by inventing various intracellular devices and scavengers to detoxify--and eventually exploit--the dangerous pollutant. Oxygen in the atmosphere was originally thought by scientists to be the reason for the proliferation of visible forms called the Cambrian explosion(because fossils of these animals were first found in Cambria, England). But an intriguin sign that oxygen prodeuction existed long before most think it did is displayed by banded iron formations--more commonly known as iron ore. These rocks show layers of relatively oxidized and non-oxidized iron, hematite and magnetite. They are probably testimony to oxygen-producing life--cyanobacteria--growing on top of each other with other bacteria long before the evolution of visible life forms.
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    0.8 billion years ag (The Proterozoic Eon)

    The height of the Proterozoic Eon was some 800 million years ago. This was still before the famous Cambrian explosion. Part of what led to the astonishing radiation of life forms today was sex--not two-parent sex leading to reproduction as we know it in mammals, but a more primordial kind. The first sort of sex to appear on our planet was the bacteria-styl genetic transfer exploited by today's genetic engineers. In this sort of sex anywhere from a few to almost all of an organism's genes can go to its partner. Bacteria-style sex was important as a way of genetically locking together symbiotic mergers between very different organisms. And it was always crucial to the biota's "reaction time": its abilitiy to respond quickly to environmental changes and emergencies. Human beings and most plants and animals simply cannot make dramatic changes in their outward appearance or metabolism by receiving visiting genes that code for at most only a few percent of their proteins. Yet in the microcosm, the implications of easy genetic exchange are staggering. For if, indeed, all strains of bacteria can potentially share all bacterial genes, then strictly speaking there are no true species in the bacterial world. All bacteria are one organism, one entity capable of genetic engineering on a planetary or global scale. In the words of Canadian bacteriologists Sorin Sonea and Maurice Panisset, this entity is, in effect "a unique, complex type of clone, composed of highly differentiated (specialized) cells." During the Proterozoic, before more familiar organisms such as the trilobites evolved, strange beings appeared which may or may not have been animals.
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    1.3 billion years ago

    According to the Book of Genesis, God halted construction of a majestically high tower in Shinar by introducing many languages. The Tower of Babel never reached heaven because its builders, stripped of their common tongue, became confused. This parable shows the importance of a universal language. While people still speak in many languages (though fewer as time goes by), the genetic code--the translation of genes into proteins--is everywhere the same. The common denominator of life extends further. Only about twenty different amino acids, linked in chains of a few dozen to several hundred, make up the proteins in all known organisms on Earth. The amino acid sequence, primarily, determines the protein's shape, and the shape determines its function. The code for translating the sequence of nucleotides in DNA to a sequence of amino acids in a protein is nearly universal. In almost all cases, a given nucleotide sequence will translate into the same amino acid sequence. Mutations are heritable changes in the quantity or sequence of DNA bases. A mutation occurs when something in the environment--radiation, say--either breaks a chemical bond or forges an uncalled-for one, and the resulting change in the DNA sequence, which confers new abilities or disabilities, is copied and passed down through the cell's descendants or causes the cell's demise. Like the dfference of an "s" between teh words laughter and slaughter, small changes or additions can have synergetic effects. The tiny Archean sacs of DNA and RNA carried out their activities prodigiously. With sleep unknown to them they grew, consumed energy and organic chemicals, and divided incessantaly. Their colonies and fibers interconnected and covered the sterile globe in a spotty film. Bacteria first expanded in the waters, where they modified the liquid and produced gases. Then they expanded to the surfaces of the sediments, where they still survive. Today the biosphere surrounds the Earth from a little deeper than six miles into the ocean to over seven miles up, above the mountaint tops at the top of the lower atmosphere.
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    2 billion years ago (The Archean Eon )

    Huge quantities of steam shot out of blow holes and splitting seams. The (Earth)lay covered in a darkening fog of carbon gases and sulfurous fumes. Showers of icy comets and carbonaceous meteorites bombarded teh planet, burning through the atmosphere to the weak and unstable surface, further rupturing the crust. Carbon and water came with them from space in sufficient quantities to add to the Earth's own supplies of what were later to become the staples of life. As the Earth's surface continued to cool, the clouds of steam filling the atmosphere could finally condense. Torrential rains fell for perhaps a hundred thousand years without cease, creating hot, shallow oceans. Submerged plate boundaries, rich in chemicals and energy, steadily vented hydrogen-rich gases into the seas. Water hitting the boiling lava in rifts and volcanoes evaporated, condensed, and rained down again. The waters began to erode the rocky landscape, smoothing out the pockmarks and wounds made by the constant belching of volcanoes and powerful impacting of meteorites. The waters round off the mountains as they were created, washing minerals and salts into the oceans and land pools. Meanwhile, in an event sometimes called the Big Belch, tectonic activity released gases trapped in the Earth's interior to form a new atmosphere of water vapor, nitrogen, argon, neon, and carbon dioxide. By this time much of the ammonnia, methane, and other hydrogen-rich gases of the primary atmosphere had been lost into space. Lightning struck. The sun continued to beam heat and ultraviolet light into the Earth's thickening atmosphere, as the fast-spinning planet spun in cycles of five-hour days and five-hour nights. The moon too had condensed from the sun's nebula. Since some 15 percent of the moon is material of Earth origin, the moon may have arisen when a planetoid crashed into the Earth's surface but could not completely escape Earthly gravity, going into orbit. Talk about trapped! Our faithful natural satellite, rather large for a puny inner planet like the Earth, from the beginning pulled rhytmically on the great bodies of water, creating tides. It is from this Archean Eon, from 3,900 to 2,500 million years ago, that we have found the first traces of life.
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  • Take me to the Early Proterozoic

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    Evolution: 3 billion years ago (The Hadean Eon)

    Where were you during the Hadean Eon 4.5 - 3.8 billion years ago? It's a good question, something like the zen koan, "where was your face before you were born?" Yet there is a physical answer. From the moment we consider origins on a cosmic scale, the view of ourselves as a part--a miniscule part--of the universe is thrust upon us. For the very atoms that compose our bodies were created not, of course, when we were conceived, but shortly after the birth of the universe itself.
    It is a known astrophysical fact that most stars in the sky are shooting away from each other at tremendous speeds. If we reverse this trend in our minds we come up with the so-called Big Bang, the hypothetical release of all the energy, matter, and antimatter in existence. Like any other look into what Shakespeare called "the dim backward and abysm of time," we must not mistake our best gueses or relatively straight-line extrapolations of present conditions into the past for the literal truth. Slight alterations in the most minor assumptions can lead to major distortions when magnified over the 15,000 million year time span that is the purported age of the present universe. Nonetheless, such extrapolations yield the best picture we have of the cosmos which preceded the evolution of life in the microcosm, as well as of the microcosm and its relentless expansion. Over the first million years of expansion after the Big Bang, the universe cooled from 100 billion degrees Kelvin, as estimated by physicist Steven Weinberg, to about 3000 degrees K, the point at which a single electron and proton could join to create hydrogen, the simplest and most abundant element in the universe. Hydrogen coalesced into supernovae--enormous clouds that over billions of years contracted from cosmic to submicrocosmic densities. Under the sheer force of gravity, the cores of the supernovae became so hot that thermonuclear reactions were fired, creating from hydrogen and various disparate subatomic particles all the heavier elements in the universe that we know today. The richness of hydrogen is in our bodies still--we contain more hydrogen atoms than any other kind--primarily in water. Our bodies of hydrogen mirror a universe of hydrogen...In the cloud of gases destined to become Earth were hydrogen, helium, carbon, nitrogen, oxygen, iron, aluminum, gold, uranium, sulfur, phosphorus, and silicon...all would have cooled and floated about as the aimless detritus of lifeless space were it not for the huge star that formed from the center of the nebula, pulling the hardening smaller bodies into orbit and igniting into a stable, long-lasting burn that bathed its satellites in continuous emanations of light, gas, and energy. At this point, about 4,600 million years ago...the sun ignited.
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  • Take me to the Archean

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    What is Life?

    We believe the question of what life is to be something of a trick: language leads us to supply a noun whereas, in truth, life is an open thermodynamic system that can persist in a dormant state but will not be alive in the vernacular sense if it is not actively transforming energy. For example, all known life is composed of astronomically carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur atoms--yet over the radiometrically dated existence of life on Earth for the past nearly four billion years life has integrated many other elements besides: calcium (found in milk and seashells), silicon (a key ingredient of computers), magnetite (used by bacteria to sense Earth's magnetic poles) and so on. Because life is continuously growing, reproducing, and evolving, it cannot be pinned down by a final definition: it is more like a verb than a noun.

    "Life is something edible, lovable, or lethal."
    James E. Lovelock

    This quote highlights the way we, and other life forms, recognize life at an unconscious level without necessarily being able to define it. The word define means to put an end on, to fix or mark the limits of, to put boundaries around in order to explain. This is difficult to do for a process in which growth and change is intrinsic. Nonetheless, because organisms have been killing each other for food, and recognizing each other for mates, for literally thousands of millions of years, we tend, like the supreme court justice who said he can't define pornography but he knows it when he sees it, to know life at a visceral level prior to academic definitions.

    It is ironic that biology textbooks, which one might expect to have the last word on the subject of life, forget even to put the first word--the definition. This is obviously due to the difficulty in providing a cogent definition of the subject at hand. Literature, by facing the problem without pretending to answer it in a final way, has sometimes fared better. Here is the great German novelist, Thomas Mann, writing in The Magic Mountain:


    "What was life? No one knew. It was undoubtedly aware of itself, so soon as it was life; but it did not know what it was...it was not matter and it was not spirit, but something between the two, a phenomenon conveyed by matter, like the rainbow on the waterfall, and like the flame. Yet why not material?--it was sentient to the point of desire and disgust, the shamelessness of matter become sensible of itself, the incontinent form of being. It was a secret and ardent stirring in the frozen chastity of the universal; it was a stolen and voluptuous impurity of sucking and secreting; an exhalation of carbonic gas and material impurities of mysterious origin and composition."

    Thomas Mann

    Scientists are beginning to restate Mann's insights more precisely:

    "Life is not a thing or a fluid any more than heat is. What we ogbswerver are some unusual sets of objects separated from the rest of the world by certain peculiar porperties such as growth, reproduction, and special ways of handling energy. These objects we elect to call 'living things.'"

    Robert Morrison

    In his famous short story, Tlon, Uqbar, Orbis Tertius, Jorge Luis Borges describes a make believe planet called Tlon in the southern hemisphere of which the inhabitants use languages that have no nouns, such that for example, they would not use the word moon but rather a verb which in English would be "to moon" or "to moonate..."'The moon rose above the river is...literally: 'upward behind the onstreaming it mooned.'...They do not say 'moon,' but rather 'round airy-light on dark' or 'pale-orange-of-the-sky' or any other such combination." (This story can be found in Labyrinths: Selected Stories & Other Writings.) But Borges's whimsical planet with its nounless southern hemisphere is a lesson for those who would like to define with an air of academic finality exactly what life is. Life is a process connected to the entire universe. Each of us, as open energy systems, is theoretically connected not only to the remotest past of the cosmos but also to its final future--if the universe has a final future. Some have suggested that that future will be one of Earth's life spread throughout the cosmos. Others suggest that the distances between the stars are so great that there is no chance we, or even our robotic offspring, will ever populate the universe.

    As Emily Dickinson put it in poem 96 (her poems were not published during her lifetime, although she is now recognized with Walt Whitman as perhaps one of the two greatest American poets):


    WHAT mystery pervades a well!
      The water lives so far,
    Like neighbor from another world
      Residing in a jar.
      
    The grass does not appear afraid;         
      I often wonder he
    Can stand so close and look so bold
      At what is dread to me.
      
    Related somehow they may be,—
      The sedge stands next the sea,         
    Where he is floorless, yet of fear
      No evidence gives he.
      
    But nature is a stranger yet;
      The ones that cite her most
    Have never passed her haunted house,         
      Nor simplified her ghost.
      
    To pity those that know her not
      Is helped by the regret
    That those who know her, know her less
      The nearer her they get.         


    For those who would like to get closer, we recommend the Sciencewriters book, What is Life?

    © 2005 by Sciencewriters