New SC project - ask a question, get explanation and a kudo!

I cannot stand the fact that I have not answered a GMAT verbal question on the forum in ages. So here is my attempt to refresh my verbal skills and answer some tough cookie questions while I am at it.

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

Concept tested: Idioms, SV agreement
Difficulty Level: Moderate
Illustration: “Rock samples” is the subject for the verb “has been dated”. Rock samples must take a plural verb.
So A and B can be instantly eliminated.
Dated at is the correct idiomatic construction.
So C and D are also eliminated
E is the correct answer choice

Tip: Though “dated at” is preferred to “dated to be”, the same construction is not necessarily true for “estimated at” and “estimated to be” construction.
“Estimated at” should be followed by a noun because “at” is a preposition.
E.g: The molten iron is estimated at 1500 degrees Celsius.
“Estimated to be” generally follows phrases
E.g: The fossil is estimated to be 1000 years old.

This is NOT a specific English rule, but the way GMAT wants things to be
Support is given by:
In OG 12, Q 27 of SC, it says that the correct idiom is "estimated to be".
However this question appears in gmatprep
"With surface temperatures estimated at minus 230 degrees Farenheit, Jupiter's moon Europa has long been considered far too cold to support life, and with 60 square miles of water though to be frozen from top to bottom."