求until
具体例子:Untiltheearly1970s,mostarchaeologistsdidnotconsiderthecoastapossiblemigrationrouteintotheAmericansbecausegeologistsoriginallybelievedthatduringthelastIceAgetheentireNorthwestCoastwascoveredbyglacialice.
我就不太明白until后面是肯定的信息的话那么其指代的时间点的前面则是否定的了么?比交困惑