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began to aggregate。 virtually all of it—99。9percent of the mass of the solar system—went to make the sun。 out of the floating materialthat was left over； two microscopic grains floated close enough together to be joined byelectrostatic forces。 this was the moment of conception for our planet。 all over the inchoatesolar system； the same was happening。 colliding dust grains formed larger and larger clumps。
eventually the clumps grew large enough to be called planetesimals。 as these endlesslybumped and collided； they fractured or split or rebined in endless random permutations；but in every encounter there was a winner； and some of the winners grew big enough todominate the orbit around which they traveled。
it all happened remarkably quickly。 to grow from a tiny cluster of grains to a baby planetsome hundreds of miles across is thought to have taken only a few tens of thousands of years。
in just 200 million years； possibly less； the earth was essentially formed； though still moltenand subject to constant bombardment from all the debris that remained floating about。
at this point； about 4。5 billion years ago； an object the size of mars crashed into earth；blowing out enough material to form a panion sphere； the moon。 within weeks； it isthought； the flung material had reassembled itself into a single clump； and within a year it had formed into the spherical rock that panions us yet。 most of the lunar material； it isthought； came from the earth’s crust； not its core； which is why the moon has so little ironwhile we have a lot。 the theory； incidentally； is almost always presented as a recent one； butin fact it was first proposed in the 1940s by reginald daly of harvard。 the only recent thingabout it is people paying any attention to it。
when earth was only about a third of its eventual size； it was probably already beginning toform an atmosphere； mostly of carbon dioxide； nitrogen； methane； and sulfur。 hardly the sortof stuff that we would associate with life； and yet from this noxious stew life formed。 carbondioxide is a powerful greenhouse gas。 this was a good thing because the sun wassignificantly dimmer back then。 had we not had the benefit of a greenhouse effect； the earthmight well have frozen over permanently； and life might never have gotten a toehold。 butsomehow life did。
for the next 500 million years the young earth continued to be pelted relentlessly byets； meteorites； and other galactic debris； which brought water to fill the oceans and theponents necessary for the successful formation of life。 it was a singularly hostileenvironment and yet somehow life got going。 some tiny bag of chemicals twitched andbecame animate。 we were on our way。
four billion years later people began to wonder how it had all happened。 and it is there thatour story next takes us。
part ii the size of the earthnature and nature’s laws lay hid innight；god said； let newton be！ and allwas light。
…alexander pope
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5THE STONE…BREAKERS
小说
at just the time that henry cavendish was pleting his experiments in london； fourhundred miles away in edinburgh another kind of concluding moment was about to take placewith the death of james hutton。 this was bad news for hutton； of course； but good news forscience as it cleared the way for a man named john playfair to rewrite hutton’s work withoutfear of embarrassment。
hutton was by all accounts a man of the keenest insights and liveliest conversation； a delightin pany； and without rival when it came to understanding the mysterious slow processesthat shaped the earth。 unfortunately； it was beyond him to set down his notions in a form thatanyone could begin to understand。 he was； as one biographer observed with an all but audiblesigh； “almost entirely innocent of rhetorical acplishments。” nearly every line he pennedwas an invitation to slumber。 here he is in his 1795 masterwork； a theory of the earth withproofs and illustrations ； discussing 。 。 。 something：
the world which we inhabit is posed of the materials； not of the earth whichwas the immediate predecessor of the present； but of the earth which； in ascendingfrom the present； we consider as the third； and which had preceded the land thatwas above the surface of the sea； while our present land was yet beneath the waterof the ocean。
yet almost singlehandedly； and quite brilliantly； he created the science of geology andtransformed our understanding of the earth。 hutton was born in 1726 into a prosperousscottish family； and enjoyed the sort of material fort that allowed him to pass much of hislife in a genially expansive round of light work and intellectual betterment。 he studiedmedicine； but found it not to his liking and turned instead to farming； which he followed in arelaxed and scientific way on the family estate in berwickshire。 tiring of field and flock； in1768 he moved to edinburgh； where he founded a successful business producing salammoniac from coal soot； and busied himself with various scientific pursuits。 edinburgh atthat time was a center of intellectual vigor； and hutton luxuriated in its enriching possibilities。
he became a leading member of a society called the oyster club； where he passed hisevenings in the pany of men such as the economist adam smith； the chemist josephblack； and the philosopher david hume； as well as such occasional visiting sparks asbenjamin franklin and james watt。
in the tradition of the day； hutton took an interest in nearly everything； from mineralogy tometaphysics。 he conducted experiments with chemicals； investigated methods of coal miningand canal building； toured salt mines； speculated on the mechanisms of heredity； collectedfossils； and propounded theories on rain； the position of air； and the laws of motion；among much else。 but his particular interest was geology。
among the questions that attracted interest in that fanatically inquisitive age was one thathad puzzled people for a very long time—namely； why ancient clamshells and other marinefossils were so often found on mountaintops。 how on earth did they get there？ those whothought they had a solution fell into two opposing camps。 one group； known as theneptunists； was convinced that everything on earth； including seashells in improbably lofty places； could be explained by rising and falling sea levels。 they believed that mountains；hills； and other features were as old as the earth itself； and were changed only when watersloshed over them during periods of global flooding。
opposing them were the plutonists； who noted that volcanoes and earthquakes； amongother enlivening agents； continually changed the face of the planet but clearly owed nothing towayward seas。 the plutonists also raised awkward questions about where all the water wentwhen it wasn’t in flood。 if there was enough of it at times to cover the alps； then where； pray；was it during times of tranquility； such as now？ their belief was that the earth was subject toprofound internal forces as well as surface ones。 however； they couldn’t convincingly explainhow all those clamshells got up there。
it was while puzzling over these matters that hutton had a series of exceptional insights。
from looking at his own farmland； he could see that soil was created by the erosion of rocksand that particles of this soil were continually washed away and carried off by streams andrivers and redeposited elsewhere。 he realized that if such a process were carried to its naturalconclusion then earth would eventually be worn quite smooth。 yet everywhere around himthere were hills。 clearly there had to be some additional process； some form of renewal anduplift； that created new hills and mountains to keep the cycle going。 the marine fossils onmountaintops； he decided； had not been deposited during floods； but had risen along with themountains themselves。 he also deduced that it was heat within the earth that created newrocks and continents and thrust up mountain chains。 it is not too much to say that geologistswouldn’t grasp the full implications of this thought for two hundred years； when finally theyadopted plate tectonics。 above all； what hutton’s theories suggested was that earth processesrequired huge amounts of time； far more than anyone had ever drea