【正文】 e way to the stati on, he chated about thei r tri p. “You’re goi ng to see som e great scenery. Goi ng eastward, you’l l pass m ountai ns and thousands of l akes and forests, as wel l as wi de ri vers and l arge ci ti es. Som e peopl e have the i dea that you can cross Canda i n l ess than fi ce days, but they fet the fact that Canada i s 5500 ki l om eters from coast to coast. H ere i n Vancouver, you’re in Canada’s warm est part. Peopl e say i t i s Canada’s m ost beauti ful ci ty, surrounded by m ountains and the Paci fi c O cean. Ski ng i n the Rocky Mountai ns and sai li ng i n the harbour m ake Vancouver one of Canada’s m ost popul ar ci ti es to l ive i n. Its popul ati on i s i ncreasi ng rapi dl y. The coast north of Vancouver has som e of the ol dest and m ost beauti ful forests i n the worl d. It is so wet there that the trees are extrem el y tal, som e m easuri ng over 90 m etres. ” That afternoon aboard the trai n, the cousi ns settl ed down i n thei r seats. Earl i er that day, when they crossed the Rocky Mountai ns, they m anaged to catch si ght of som e m ountai n goats and even a gri zzl y bear and an eagl e. Thei r next stop was Cal gary, whi ch i s fam ous for the Cal gary Stam pede. Cowboys from al l over the worl d e to pete i n the Stam pede. Many of them have a gi ft for ri di ng wi l d horses and can wi n thousands of dol l ars i n pri zes. After two days’ travel , the gi rl s began to real i ze that Canada i s qui te em pty. At school , they had l earned that m ost Canadi ans l i ve wi thi n a few hundred ki l om etres of the USA border, and Canada’s popul ati on i s onl y sl i ghtl y over thi rty m i l l i on, but now they were am azed to see such an em pty country. They went through a wheatgrowi ng provi nce one knows exactl y how the earth began, as i t happened so long ago. H owever, acording to a wi del y accepted theory, the universe began wi th a “ Bi g Bang “ that threw m ater i n al di recti ons. After that, atoms began to form and bi ng to create stars and other bodi es. For several bi l i on years after the “ Bi g Bang “, the earth was sti l just a cl oud of dust. What i t was to be e was uncertai n unti l between 4. 5 and 3. 8 bil li on years ago when the dust settl ed i nto a soli d gl obe. The earthenware becam e so vi olent that i t was not cl ear whether the shape woul d l ast or not. It expl oded l oudl y wi th fi re and rock. They were i n tim e to produce carbon, ni trogen , water vapour and other gases , whi ch were to m ake the earth’s atm osphere. What i s even m ore im prtant i s that as the earth cool ed down, water began to apear on i ts surface. Water had al so appeared on other pl as li ke Mars but, unli ke the earth, i t had di sappeared later. It was not imm edi atel y obvi ous that water was to be fundam ental to the devel opm ent of l i fe. What m any sci enti sts beli eve i s that the conti nued persence of water al l owed the earth to dissolve harm ful gases and aci ds i nto the oceans and seas. Thi s produced a chain reacti on, whi ch m ade i t possi bl e for li fe to develop. Many m il i ons of years l ater, the fi rst extrem el y smal pl ants began to appear on the surface of the water. They m ul ti pli ed and fi l ed the oceans and seas wi th oxygen, whi ch encouraged the l ater devel opm ent of earl y shel l fi sh and al sorts of fi sh. N ext, green pl ants began to grow on land. They were fol owed i n tim e by l and anim al s. Som e were insects. O thers, cal l ed am phi bi ans, were abl e to li ve on l and as wel l as i n the water. Later when the pl ants grew i nto forests, repti l es appeared for the fi rst ti m e. They produced young general y by layi ng eggs. After that, som e huge anim als, cal ed di nosaurs, devel oped. They l ai d eggs to and exi sted on the earth for m ore than 140 m il li on years. H owever, 65 m il li on years ago the age of the di nosaurs ended. Why they suddenl y di sappeared sti l rem ai ns a m ystery. Thi s di sappearance m ade possi bl e thief ri se of m amm al s on the earth. These anim al s were di fferent from al l li fe form s i n the past, because they Gavi n birth to young baby anim als and prodeced m il k to feed them. Fi nnal y about 2. 6 mi l i on years ago som e sm al cel ver anim als, now wi th hands and feet, appeared and spread al over the earth. Thus they have, i n thei r turn, be e the m ost im portant ani m al s on the pl a. But they no they l ooki ng after the earth very wel. They are putti ng too m uch carbon di oxi de i nto the atm osphere, whi ch prevenrs heat from escapi ng from the earth into space. As a result of thi s, m any sci enti sts beli eve the earth m ay b e too hot to l i ve on. So whether li fe wi l conti nue on the earth for mi l i ons of years to e wi l depend on whether thi s probl em can be solved. A vi si t to the m oon Last m onth I was l ucky engough to have a chance to make a tri p i nto space wi th m y fri end Li Yanpi ng, an astronom er. We vi si ted the m on i n our spaceshi p! Before we l eave, Li Yanpi ng expl ai ned to m e that the forece of the gravi ty woul d change three tim es on our journey and that the fi rst change woul d be the m ost powerful. Then we were off. As the rocket rose i nto the air, we were pushed back i nto our seats because we were tryi ng to escape the pul l of the earth’s gravi ty. It was so hard that we coul d not say anythi ng to each other. Gradual ly the weight l essened and I was abl e to tal k to him. “ Why is the spaceship not fal li ng back to the earth? O n the earth if I fal l from a tree I wil l fal l to ground. ” I asked. “ We are too far from the earth now to fel i ts pul l, “ he expl ai ned, “ so we feel as i f there i s no gravi ty at al . When we get cl oser to the m on, we shal feel i ts gravi ty pul li ng us, but it wi l not be as strong a pul l as the earth’s. “ I cheered up im m edi atel y and fl oated wei g