TPO 08 恐龍滅絕 - 英檢

Many plants and animals disappear abruptly from the fossil record as one moves
from layers of rock documenting the end ofthe Cretaceous up into rocks
representing the beginning of the Cenozoic (the era after the Mesozoic).

可以拆解和翻譯一下這句嗎?有點是懂非懂


第十題

Paragraph 5 lr has not been common at Earth’s since the very beginning of
the planet’s history. Because it usually exists in a metallic state, it was
preferentially incorporated in Earth’s core as the planet cooled and
consolidated. lr is found in high concentrations in some meteorites, in which
the solar system’s original chemical composition is preserved. Even today,
microscopic meteorites continually bombard Earth, falling on both land and sea.
By measuring how many of these meteorites fall to Earth over a given period of
time, scientists can estimate how long it might have taken to deposit the
observed amount of lr in the boundary clay. These calculations suggest that a
period of about one million years would have been required. However, other
reliable evidence suggests that the deposition of the boundary clay could not
have taken one million years. So the unusually high concentration of lr seems
to require a special explanation.

10. Paragraph 5 implies that a special explanation of lr in the boundary clay
is needed because

○the lr in microscopic meteorites reaching Earth during the Cretaceous
period would have been incorporated into Earth’s core

○the lr in the boundary clay was deposited much more than a million years ago

○the concentration of lr in the boundary clay is higher than in microscopic
meteorites

○the amount of lr in the boundary clay is too great to have come from
microscopic meteorites during the time the boundary clay was deposited

不太懂為什麼答案是D?
為什麼銥的量會太多而不可能是來自隕石?
這一題從哪推出答案是D?


感謝回答

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