Official 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.

Option A
Option B
Option C
Option D
Option E

(This question is from Official Guide. Therefore, because of copyrights, the complete question cannot be copied here. You can access the question on GMAT Club)

Solution

Meaning Analysis

Let’s break down the sentence to better understand it:

• Rock samples (Main Subject)
  • taken from the remains of an asteroid (verb-ed modifier – provides additional info about ‘rock samples’)
    • about twice the size of the 6-mile-wide asteroid (modifier – provides additional information about ‘an asteroid’)
      • that eradicated the dinosaurs (clause modifier – provides additional information about ‘6-mile-wide asteroid’)
• has been dated to be 3.47 billion years old (‘has been’ – Main Verb 1)
• and thus is evidence of the earliest known asteroid impact on Earth. (‘is’ – Main Verb 2)

The sentence talks about the rock samples that have been taken from the remains of an asteroid. The sentence provides additional information about this asteroid; it says that this asteroid is about two times the size of another asteroid that was 6-miles wide and eradicated the dinosaurs.

The rock samples have been found to be 3.47 billion years old, and since they are so old, they are evidence of the earliest known asteroid impact on Earth.

Error Analysis

There are two errors in the original sentence:

1. The subject of the sentence (Rock samples) is plural while both the verbs (“has been” and “is”) are singular. Since the subject is in the non-underlined part, the verbs need to be changed into plural form.
2. “dated to be” is not idiomatically correct. “dated at” is the correct idiom. (Just remember this idiom; there’s nothing to understand or explain here)

Option Analysis

(A) Incorrect. For the reasons discussed above.

(B) Incorrect. “has been” is singular while the subject is plural. Secondly, we need a verb after ‘and’ since “has been dated” cannot go with “evidence”.

(C) Incorrect. For the incorrect idiom “dated to be”. The correct idiom is “dated at”.

(D) Incorrect. “dated as being” is incorrect. The correct idiom is “dated at”. Secondly, we need a verb after ‘and’ since “have been dated” cannot go with “evidence”.

(E) Correct. Both the original errors have been corrected in this option, and no new errors have been introduced.

Additional Notes

From this question, we have learnt that “dated to be” is incorrect while “dated at” is correct.

Rock samples have been dated to be 3.47 billion years old. (Incorrect)

Rock samples have been dated at 3.47 billion years old. (Correct)

Now, it will help us to know that “estimated to be” is correct. Therefore, the above sentence can be written as:

Rock samples have been estimated to be 3.47 billion years old. (Correct)

Whereas

Rock samples have been estimated at 3.47 billion years old. (Incorrect)

Official Question OG13 Q30 plays on exactly the above usage of “estimated at” and “estimated to be”. (Click here for the question)

However, it doesn’t mean that “estimated at” is always wrong, as “estimated at” has been used in the below official sentence:

With surface temperatures estimated at minus 230 degrees Fahrenheit, Jupiter’s moon Europa has long been considered far too cold to support life, and with 60 square miles of water thought to be frozen from top to bottom. (Click here for the complete question)