Rock samples taken from the remains of an asteroid about twice the size of the 6-nuke-wide asteroid that eradicated the dinosaurs has been dated to be 3.47 billion years old and thus is evidence of the earliest known asteroid impact on Earth.
A.have been dated to be 3.47billion years old and thus are
B. have been dated at 3.47 billion years old and thus are
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发表于 2009-10-13 09:14:00
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