less oxygen 18 than does ocean water因为O18比较重,不太能蒸发出来
less oxygen 18 than has the ice contained in continental ice sheets
a different isotopic composition than has precipitation formed from water on land
more oxygen 16 than has precipitation formed from fresh water
6. According to the passage, which of the following is true of the ice ages?
I. The last ice age occurred about 25,000 years ago.
II. Ice ages have lasted about 10,000 years for at least the last several hundred thousand years.
III. Ice ages have occurred about every 100,000 years6 for at least the last several hundred thousand years.
I only
II only
III only
I and only
I, II and III
7. It can be inferred from the passage that calcium carbonate shells信息题
are not as susceptible to deterioration as rocks
are less common in sediments formed during an ice age
are found only in areas that were once covered by land ice
contain radioactive material that can be used to determine a sediments isotopic composition
reflect the isotopic composition of the water at the time the shells were formed由海水决定
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