Likeallsocietieswhoseoriginspredatetheinventionofthewrittenword,manyaspectsofprehistoricTibetarelostinablurofmystery.YetarcheologistsarediggingintotheruinsleftbyTibet'searliesthumaninhabitantstohelpcarveawaythelackofknowledge,justasarthistoriansareexaminingancientpaintingsleftinsideTibetancavestosketchoutthecontoursofprehistoriclifeandartontheRoofoftheWorld.