Earth changes between ice ages and warm periods in a（n） （41）___that includes several cycles，including a （42）___ one that lasts 100，000years．Scientists （43）___suggested this cycle might be due to changes in the inflow of cosmic（宇宙） dust．
The idea is that Earth （44）___above and below the imaginary planet that runs through the sun and Jupiter（木星），completing a cycle every 100，000years．So maybe it encounters （45）___varying amounts of dust during each cycle that produce the climate trend．
Now there is some （46）___，from ancient cosmic dust recovered in ocean-floor drilling near the Azores islands west of Portugal．The large quantity of the dust rises and falls with a wonderful 100，000year cycle during the period analyzed，253，000years to 458，000years ago．Periods of more dust are related to（47）___ climates．
But that is a long way from showing that the dust （48）___climate．Some scientists argue that it is not clear how cosmic dust would make the climate warmer while dust from volcanoes is known to make it cooler．They say the cosmic dust is so thin that it is hard to see how it could have any climate（49）___．
Nevertheless，the new study shows scientists have to take the cosmic dust idea seriously．
