Arrange the following Geological periods of the earth from the oldest to the newest one.
(a) Triassic Period
(b) Carboniferous Period
(c) Cambrian Period
(d) Quaternary Period
(e) Permian Period

Question

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Correct — option (4), which reads (c), (b), (e), (a), (d). The question asks for the order from the oldest period to the newest, so each item has to be placed on the geological time scale and then read forward in time. The Cambrian at (c) is by far the oldest of the five: it opens the Palaeozoic era and the Phanerozoic eon at about 539 million years ago and runs to about 487 million years ago, and it is the period of the great diversification of hard-shelled marine animals that gives it its fame. The Carboniferous at (b) comes next, from about 359 to about 299 million years ago, the fifth period of the Palaeozoic and the age of the vast coal-forming swamp forests that give the period its name. The Permian at (e) follows immediately, about 299 to 252 million years ago, and it is the last period of the Palaeozoic; it ends at 251.9 million years ago in the Permian-Triassic extinction, the largest extinction event of the Phanerozoic. The Triassic at (a) is next, from 251.902 to 201.4 million years ago — the first and shortest period of the Mesozoic era, opening in the aftermath of that extinction. The Quaternary at (d) is the youngest of all, running from 2.58 million years ago to the present day as the last period of the Cenozoic. Read forward, that gives Cambrian, Carboniferous, Permian, Triassic, Quaternary, which is (c), (b), (e), (a), (d) — the row printed at option (4). Two things make the question easier than it looks. The first is that only one row begins with the Cambrian; the second is that only one row ends with the Quaternary, and it is the same row. Either observation alone settles the question.

Why the other options are wrong — (a) This row opens with the Carboniferous and puts the Cambrian third, which reverses the two ends of the Palaeozoic. The Cambrian begins the Palaeozoic at about 539 million years ago and the Carboniferous is its fifth period, starting about 359 million years ago, so 180 million years separate them and nothing can put the Carboniferous first. The row then closes with the Permian, placing it after the Quaternary — that is, making the last period of the Palaeozoic younger than the period we are living in. Since the question asks for oldest to newest, the last item in a correct row must be the youngest of the five, and only the Quaternary, which began 2.58 million years ago, can hold that place. Checking the first and last cells of an ordering row before reading the middle disposes of this option immediately.  (b) This row also begins with the Carboniferous, which cannot be right in an oldest-to-newest sequence that contains the Cambrian, the period that opens the whole Palaeozoic era 180 million years earlier. Its interior is nearer the truth than the other wrong rows — it does keep the Cambrian before the Triassic and the Permian before the Quaternary — and that is what makes it dangerous, because a candidate who checks a pair or two in the middle will find them plausible and accept the row. The test that never fails on an ordering question is positional rather than relational: identify the extreme member of the sequence, here the Cambrian as the oldest, and strike out every row that does not open with it. That leaves one row standing.  (c) This row is the sequence run almost backwards. It opens with the Quaternary, which began 2.58 million years ago and is the youngest period on the whole scale, and it closes with the Cambrian, which is the oldest of the five. In other words it answers the ascending question when the stem asked for the descent from oldest to newest — the same reversal trap that this paper sets again a few questions later, where the stem turns on the words 'descending order'. The ordering word in the stem is the question, and it should be read and underlined before the rows are looked at. Once the direction is fixed, a row that opens with the youngest item can be struck out without reading any of its remaining cells.

Concept: The geological time scale divides the earth's past into eons, eras, periods and epochs, with boundaries fixed by the International Commission on Stratigraphy at points in the rock record, most of them marked by a change in the fossils preserved. The Phanerozoic eon, the eon of visible life, begins with the Cambrian at about 539 million years ago and is split into three eras. The Palaeozoic runs from the Cambrian through the Ordovician, Silurian, Devonian, Carboniferous and Permian, ending 251.9 million years ago; it takes in the Cambrian explosion of marine life, the colonisation of the land by plants and then by animals, and the coal swamps of the Carboniferous. The Mesozoic follows with the Triassic, Jurassic and Cretaceous, the era of the dinosaurs, and ends 66 million years ago with the extinction that removed them. The Cenozoic runs from then to now, with the Palaeogene, Neogene and Quaternary periods; the Quaternary, from 2.58 million years ago, holds the Pleistocene ice ages and the Holocene in which agriculture and civilisation appear. Two mass extinctions define the era boundaries here — the Permian-Triassic event at 251.9 million years ago, the largest of the Phanerozoic, and the Cretaceous-Palaeogene event at 66 million years ago.

State PCS 2021 Q23 — Geography PYQ with Answer

State PCS 2021 Q23 — Geography PYQ with Answer