Complete the following passage by using the words in the box. Each word can only be used once. Note that there is one word more than you need.
Earth changes between ice ages and warm periods in a(n) __小题1:__ that includes several cycles, including a __小题2:_ one that lasts 100,000 years. Scientists __小题3:__suggested this cycle might be due to changes in the inflow of cosmic(宇宙) dust. The idea is that Earth _小题4:__above and below the imaginary plane that runs through the sun and Jupiter(木星), completing a cycle every 100,000 years. So maybe it encounters __小题5:_varying amounts of dust during each cycle that produce the climate trend. Now there is some __小题6:__, 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 100,000 year cycle during the period analyzed, 253,000 years to 458,000 years ago. Periods of more dust are related to__小题7:__ climates. But that is a long way from showing that the dust __小题8:__ 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__小题9:__. Nevertheless, the new study shows scientists have to take the cosmic dust idea seriously. |