八年级英语下册Unit7文化拓展沪教牛津版

Anyone out thereScientists thinkthat therehas beenlife onthe Earthfor hundredsof millionsofyears.However,we havenot foundlife onany otherplanets yet.The Earthis aplanet andit goesaround theSun.Seven otherplanets alsogo aroundtheSun.None of them hasan environmentlike thatoftheEarth,so scientistsdo notthinkthey willfind lifeon them.The Sunand itsplanets arecalled theSolar System,and ourSolar System isa smallpart ofa muchlarger groupof starsand planets,called the Galaxyor theMilky Way.There arebillions ofstars in theGalaxy,and ourSun isonly oneofthem.Scientists havealso discoveredmany othergalaxies inthe universe.They areveryfar awayand theirlight hasto travelfor manyyears toreach us.So howlarge istheuniverse Itis impossibleto imagine.Scientists havesent spaceshipsto theplanet Marsto takephotos.They haveeven sentspaceshipsto traveloutside theSolarSystem.However,no spaceshiphas travelledfarenough toreach otherstars inour Galaxy.Scientists havealways askedthe questionswith somany starsintheuniverse,arewe alone,or isthere lifeouttherein spaceHave therebeen visitorsto theEarth fromotherplanets Whyhas noone municatedwith usWe donot knowthe answers...yet.。