The diagram shows, in three column groupings, various divisions of Ear

Hi Ladies and Gentlemen,

It's my first post here although I often read your forums. I tried an integrated reasoning problem for the first time today and for the most part did fine. However, I'm confused by the answer on this sample problem from the GMAT site:

The board won't allow me to post pictures but the question is from the official GMAT site's integrated reasoning sample questions.

The diagram shows, in three column groupings, various divisions of Earth's geological history since its formation approximately 4,600 million years ago. In the leftmost column grouping, the Precambrian eon is subdivided into chronometric eons shown on the far left; but otherwise, in the rest of the graphic, each subsequent column to the right shows the subdivisions of the timeframes to its left. Each of the rightmost two column groupings is a magnification—with additional information—of a portion of the grouping directly to its left.

Fill each blank using the drop-down menu to create the most accurate statement on the basis of the information provided.

The Miocene epoch spans closest to (3%, 25%, 85%) of the era of which it is a part.

According to the diagram the beginning of the (Cambrian period, Triassic Period, Pliocene Epoch, Precambrian eon) marks the onset of a new eon, era, and period in geological history.






I'm confused by the answer to the second question. The beginning of the Cambrian period does not coincide with the onset of a new eon, era, and period. If I'm reading it wrong, I apologize for wasting your time.

Hi,

Though I am not sure where your confusion lies but let me have a try.

Basically, if you look at the first figure from the left, you can see that there are only two eons: Precambrian and Phanerozoic.

Now, for anything to start with an eon, it has to start with either Precambrian eon or Phanerozoic eon.

However, there is no information about eras or periods at the beginning of Precambrian eon.

So, the only solution possible which can start with eon, era and period, will be the one starting with Phanerozoic eon.

Now that is the case with Cambrian period. For this, Phanerozoic eon starts, Paleozoic era starts and Cambrian period starts. Therefore, this is the correct answer.

In addition, you can see that the answer also could have been Phanerozoic eon. (same three times start in this case also).

Hope this helps

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Thanks,
Chiranjeev