Geologists Have Proposed The Term Eon For The Largest Divisions GMAT Reading Comprehension

Reading Passage Question

This passage is excerpted from The Earth Through Time, 7th Edition, by Harold L. Levin (Wiley):

Geologists have proposed the term eon for the largest divisions of the geologic time scale. In chronological succession, the eons of geologic time are the Hadean, Archean, Proterozoic, and Phanerozoic. The beginning of the Archean corresponds approximately to the ages of the oldest known rocks on Earth. Although not universally used, the term Hadean refers to that period of time for which we have no rock record, which began with the origin of the planet 4.6 billion years ago. The Proterozoic Eon refers to the time interval from 2,500 to 544 million years ago.

The rocks of the Archean and Proterozoic are informally referred to as Precambrian. The antiquity of Precambrian rocks was recognized in the mid-1700s by Johann G. Lehman, a professor of mineralogy in Berlin, who referred to them as the “Primary Series.” One frequently finds this term in the writing of French and Italian geologists who were contemporaries of Lehman. In 1833, the term appeared again when Lyell used it in his formation of a surprisingly modern geologic time scale. Lyell and his predecessors recognized these “primary” rocks by their crystalline character and took their uppermost boundary to be an unconformity that separated them from the overlying — and therefore younger — fossiliferous strata.

The remainder of geologic time is included in the Phanerozoic Eon. As a result of careful study of the superposition of rock bodies accompanied by correlations based on the abundant fossil record of the Phanerozoic, geologists have divided it into three major subdivisions, termed eras. The oldest is the Paleozoic Era, which we now know lasted about 300 million years. Following the Paleozoic is the Mesozoic Era, which continued for about 179 million years. The Cenozoic Era, in which we are now living, began about 65 million years ago.

“Geologists have proposed the term eon for the largest divisions”- is a GMAT reading comprehension passage with answers. Nominees must have a firm understanding of English GMAT reading comprehension. There are two comprehension questions in this GMAT Reading Comprehension section. GMAT Reading Comprehension questions are conducted to examine candidates' skills to decipher, interpret, and utilize knowledge or ideas. Candidates can actively prepare by answering GMAT Reading Comprehension Practice Questions.

Solutions and Explanation

  1. The passage uses all the following terms to describe eons or eras, except

(A) Archean
(B) Paleozoic
(C) Holocene
(D) Phanerozoic
(E) Cenozoic

Answer: C
Explanation:
The first passage uses the terms Hadean, Archean, Proterozoic, and Phanerozoic to describe Eon. The second passage uses the terms Paleozoic Era, Mesozoic Era, and Cenozoic Era to describe Era. All of the terms given in the options are therefore included except the term Holocene. Therefore the third option is the right answer.

  1. Which of the following terms is not used in the passage to describe rocks that are more than 544 million years old?

(A) Precambrian
(B) Cenozoic
(C) Primary Series
(D) Archean
(E) Proterozoic

Answer: B
Explanation:
The second option is the right answer. This is due to the passage's explicit statement that the Cenozoic Era, in which we currently live, started approximately 65 million years ago. The rest of the options are all wrong answers because they are indeed used in the passage to classify rocks that are present in the question’s particular timeline.

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