按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
t couldn’t wait to get going； but then； having gottengoing； it seemed in very little hurry to move on。
consider the lichen。 lichens are just about the hardiest visible organisms on earth； butamong the least ambitious。 they will grow happily enough in a sunny churchyard； but theyparticularly thrive in environments where no other organism would go—on blowymountaintops and arctic wastes； wherever there is little but rock and rain and cold； and almostno petition。 in areas of antarctica where virtually nothing else will grow； you can findvast expanses of lichen—four hundred types of them—adhering devotedly to every wind…whipped rock。
for a long time； people couldn’t understand how they did it。 because lichens grew on barerock without evident nourishment or the production of seeds； many people—educatedpeople—believed they were stones caught in the process of being plants。 “spontaneously；inorganic stone bees living plant！” rejoiced one observer； a dr。 homschuch； in 1819。
closer inspection showed that lichens were more interesting than magical。 they are in facta partnership between fungi and algae。 the fungi excrete acids that dissolve the surface of therock； freeing minerals that the algae convert into food sufficient to sustain both。 it is not avery exciting arrangement； but it is a conspicuously successful one。 the world has more thantwenty thousand species of lichens。
like most things that thrive in harsh environments； lichens are slow…growing。 it may take alichen more than half a century to attain the dimensions of a shirt button。 those the size ofdinner plates； writes david attenborough； are therefore “likely to be hundreds if notthousands of years old。” it would be hard to imagine a less fulfilling existence。 “they simplyexist；” attenborough adds； “testifying to the moving fact that life even at its simplest leveloccurs； apparently； just for its own sake。”
it is easy to overlook this thought that life just is。 as humans we are inclined to feel that lifemust have a point。 we have plans and aspirations and desires。 we want to take constantadvantage of all the intoxicating existence we’ve been endowed with。 but what’s life to alichen？ yet its impulse to exist； to be； is every bit as strong as ours—arguably even stronger。
if i were told that i had to spend decades being a furry growth on a rock in the woods； ibelieve i would lose the will to go on。 lichens don’t。 like virtually all living things； they willsuffer any hardship； endure any insult； for a moment’s additional existence。 life； in short； justwants to be。 but—and here’s an interesting point—for the most part it doesn’t want to bemuch。
this is perhaps a little odd because life has had plenty of time to develop ambitions。 if youimagine the 4；500…billion…odd years of earth’s history pressed into a normal earthly day；then life begins very early； about 4a。m。； with the rise of the first simple； single…celled organisms； but then advances no further for the next sixteen hours。 not until almost 8：30 inthe evening； with the day five…sixths over； has earth anything to show the universe but arestless skin of microbes。 then； finally； the first sea plants appear； followed twenty minuteslater by the first jellyfish and the enigmatic ediacaran fauna first seen by reginald sprigg inaustralia。 at 9：04p。m。 trilobites swim onto the scene； followed more or less immediately bythe shapely creatures of the burgess shale。 just before 10p。m。 plants begin to pop up on theland。 soon after； with less than two hours left in the day； the first land creatures follow。
thanks to ten minutes or so of balmy weather； by 10：24 the earth is covered in the greatcarboniferous forests whose residues give us all our coal； and the first winged insects areevident。 dinosaurs plod onto the scene just before 11p。m。 and hold sway for about three…quarters of an hour。 at twenty…one minutes to midnight they vanish and the age of mammalsbegins。 humans emerge one minute and seventeen seconds before midnight。 the whole of ourrecorded history； on this scale； would be no more than a few seconds； a single human lifetimebarely an instant。 throughout this greatly speeded…up day continents slide about and bangtogether at a clip that seems positively reckless。 mountains rise and melt away； ocean basinse and go； ice sheets advance and withdraw。 and throughout the whole； about three timesevery minute； somewhere on the planet there is a flashbulb pop of light marking the impact ofa manson…sized meteor or one even larger。 it’s a wonder that anything at all can survive insuch a pummeled and unsettled environment。 in fact； not many things do for long。
perhaps an even more effective way of grasping our extreme recentness as a part of this4。5…billion…year…old picture is to stretch your arms to their fullest extent and imagine thatwidth as the entire history of the earth。 on this scale； according to john mcphee in basin andrange； the distance from the fingertips of one hand to the wrist of the other is precambrian。
all of plex life is in one hand； “and in a single stroke with a medium…grained nail file youcould eradicate human history。”
fortunately； that moment hasn’t happened； but the chances are good that it will。 i don’twish to interject a note of gloom just at this point； but the fact is that there is one otherextremely pertinent quality about life on earth： it goes extinct。 quite regularly。 for all thetrouble they take to assemble and preserve themselves； species crumple and die remarkablyroutinely。 and the more plex they get； the more quickly they appear to go extinct。 whichis perhaps one reason why so much of life isn’t terribly ambitious。
so anytime life does something bold it is quite an event； and few occasions were moreeventful than when life moved on to the next stage in our narrative and came out of the sea。
land was a formidable environment： hot； dry； bathed in intense ultraviolet radiation；lacking the buoyancy that makes movement in water paratively effortless。 to live onland； creatures had to undergo wholesale revisions of their anatomies。 hold a fish at each endand it sags in the middle； its backbone too weak to support it。 to survive out of water； marinecre