Question

Rock samples taken from the remains of an asteroid about twice the size of the 6-mile-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. Has been dated to be 3.47 billion years old and
  thus is
• B. Has been dated at 3.47 billion years old and thus
• C. Have been dated to be 3.47 billion years old and
  thus are
• D. Have been dated as being 3.47 billion years old
  and thus
• E. Have been dated at 3.47 billion years old and
  thus are

Answer 1

The correct option is E Have been dated at 3.47 billion years old and

thus are
The plural subject of this sentence, Rock samples, requires plural verb phrases-have been dated and are rather than has been dated and is. The idiomatic way of expressing estimation of age is with the phrase dated at.
The plural verbs match the plural subject, and the wording of the sentence is idiomatic.