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ThiswouldhavecreatedabarrieroficeextendingfromtheAlaskaPeninsula,throughtheGulfofAlaskaandsouthwardalongtheNorthwestCoastofnorthAmericatowhatistodaythestateofWashington.Hetheorizedthatwiththeuseofwatercraft,peoplegraduallycolonizedunglaciatedrefugesandareasalongthecontinentalshelfexposedbythelowersealevel.Thefirstwatercrafttheoryaboutthismigrationwasthataround11,000-12,000yearsagotherewasanice-freecorridorstretchingfromeasternBeringiatotheareasofNorthAmericasouthofthegreatnorthernglaciers.Butbeliefinthisice-freecorridorbegantocrumblewhenpaleoecologistGlenMacDonalddemonstratedthatsomeofthemostimportantradiocarbondatesusedtosupporttheexistenceofanice-freecorridorwereincorrect.Thecoastalhypothesishasgainedincreasingsupportinrecentyearsbecausetheremainsoflargelandanimals,suchascaribouandbrownbears,havebeenfoundinsoutheasternAlaskadatingbetween10,000and12,500yearsago.Thecoastalhypothesissuggestsaneconomybasedonmarinemammalhunting,saltwaterfishing,shellfishgathering,andtheuseofwatercraft.Inaddition,therewasanimportantgroupofsculpturesmadeforreligioususe,themajorityofwhichwereproducedinearthenware.WhitewaresproducedinHebeiandHenanprovincesfromtheseventhtothetenthcenturiesevolvedintothehighlyprizedporcelainsoftheSongdynasty(AD.960-1279),longregardedasoneofthehighpointsinthehistoryofChina'sceramicindustry.Oneofthemostfar-reachingexamplesistheimpactofthefineninth-centuryAD.ChineseporcelainwaresimportedintotheArabworld.CobaltoresfoundinChinahaveahighmanganesecontent,whichproducesamoremutedblue-graycolor.