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Nature, we believe, takes forever.  It moves with infinite slowness throught the many periods of its history, whose names we dimly recall from high school biology - the Devonian, the Triassic, the Cretaceous, the Pleistocene.  Ever since Darwin, nature writers have taken pains to stress the incomprehensible length of this path.  "So slowly, oh, so slowly have the great changes been brought about," wrote John Burroughs at the turn of the century.  "The Orientals try to get a hint of eternity by saying that when the Himalayas have been ground to a powder by allowing a gauze veil t o float against them once in a thousand years, eternity will have only just begun.  Our mountains have been pulverized by a process almost as slow."  We have been told that man's tenure is as a minute to the earth's day, but it is that vast day which has lodged in our minds.  The age of the trilobites began some 600 million years ago.  The dinosaurs lived for nearly 140 million years.  Since even a million years is utterly unfathomable, the message is:  Nothinkg happens quickly.  Change takes unimaginable - "geologic"- time.

This idea about time is essentially mistaken.  Muddled though they are scientifically, the creationists, believing in the sudden appearance of hte earth some seven thousand years ago, may intuitively understand more about hte progress of time than hte rest of us.  For the world as we know it - that is, the world with human beings formed into some sort of civilization, the world in which North America, Europe, and much of the rest of the planet are warm enough to support large human populations - is of quite comprehensible duration.  People began to collect in a rudimentary society in the north of Mesopotamia some ten or twelve thousand years ago.  Using thirty years as a generation, that is three hundred and thirty to four hundred generations ago.  Sitting here at my desk, I can think back five generations in my family - I have seen photos of four.  That is, I can think back nearly one-sixtieth of the way to the start of civilization.  A skilled geneaologist might get me one-thirtieth of the distance back.  And I can conceive of how most of those forebears lived.  From the work of archaeologists and from accounts like those in the Bible I have some sense of daily life at least as far back as the time of the pharaohs, which is more than a third of the way. Two hundred and sixty-five generations ago Jericho was a walled city of three thousand souls.  Two hundred and sixty-five is a large number, but not in the way that six million is a large number - not inscrutably large.

Or look at it this way: There are plants on this earth as old as civilization.  Not species - individual plants.  The General Sherman tree in California's Sequoia National Park may be a third as old, about four thousand years.  Certain Antarctic lichens date back ten thousand years.  A specific creosote plant in the Southwestern desert was estimated recently to be 11,700 years of age.

And within that ten or twelve thousand years of civilization, of course, time is not uniform.  The world as we really, really know it dates back to the Industrial Revolution.  the world we actually feel comfortable in dates back to perhaps 1945.  It was not until after World War II, for instance, that plastics came into widespread use.

In other words, our reassuring sense of a timeless future, which is drawn from that apparently bottomless well of the past, is a delusion.  True, evolution, grinding on ever so slowly, has taken billions of years to create us from slime, but that does not mean that time always moves so ponderously.  Events, enormous events, can happen quickly.  We've known this to be true since Hiroshima, of course, but I don't mean that quickly.  I mean that over a year or a decade or a lifetime big and impersonal and dramatic changes can take place.  We're now comfortable with the bizarre idea that continents can drift over eons, or that continent can die in an atomic second; even so, normal time seems to us immune to such huge changes.  It isn't, though.  In the last three decades, for example, the amount of carbon dioxide in the atmosphere has increased more than 10 percent, from about 315 to more than 350 parts per million.  In the last decade, an immense "hole" in the ozone layer has opened above  the South Pole.  In the last half-decade, the percentage of West German forests damaged by acid rain has risen from less than 10 to more than 50.  According to the Worldwatch Institute, in 1988 - for perhaps the first time since that starved Pilgrim winter at Plymouth - America ate more food than it grew.  Burroughs again:  "One summer day, while I was walking along the country rode on the farm where I was born, a section of the stone wall opposite me, and not more than three or four yards distant, suddenly fell down.  Amid the general stillness and immobility around me, the effect was quite startling ... It was the sudden summing up of half a century or more of atomic changes in the wall.  A grain or two of sand yielded to the pressure of long years, and gravity did the rest."