Which of the following is/are correct sequences in reference to geological period ?
(A) Triassic → Jurassic → Cretaceus
(B) Paleozoic ← Mesozoic ← Cenozoic
(C) Devonian ← Silurian ← Carboniferous

Question

Which of the following is/are correct sequences in reference to geological period ? 
(A) Triassic → Jurassic → Cretaceus 
(B) Paleozoic ← Mesozoic ← Cenozoic 
(C) Devonian ← Silurian ← Carboniferous

Accepted Answer

The correct option is 1: Both (A) and (B)

Understanding the geological time scale requires knowing the correct chronological order of Eons, Eras, and Periods. The arrow in the sequence always indicates the direction of time, either moving forward (from older to younger, as in A) or moving backward (from younger to older, as in B).

Sequence (A) is **Triassic → Jurassic → Cretaceus**. This sequence correctly represents the progression of geological time from older to younger periods within the Mesozoic Era, which is popularly known as the 'Age of Dinosaurs'. The Triassic Period began approximately 251.9 million years ago and was succeeded by the Jurassic Period (201.3 million years ago), which was then followed by the Cretaceous Period (145 million years ago). Therefore, reading left-to-right, this sequence is entirely correct chronologically.

Sequence (B) is **Paleozoic ← Mesozoic ← Cenozoic**. This sequence is written in reverse chronological order, with the arrows pointing towards the older Era. Reading right-to-left: The Cenozoic Era is the current and youngest era, dating from 66 million years ago to the present. The Mesozoic Era (252–66 million years ago) immediately preceded the Cenozoic. The Paleozoic Era (541–252 million years ago) preceded the Mesozoic. Since Cenozoic is younger than Mesozoic, and Mesozoic is younger than Paleozoic, the sequence correctly establishes the relative ages of these three Eras. Both sequences (A) and (B) are accurate representations of the geological timescale, making the combined option the correct choice.

The incorrect option is 2: Only (B)

This option is incorrect because, while statement (B) is a correct chronological sequence of Eras (Cenozoic is youngest, Mesozoic is next oldest, and Paleozoic is oldest), statement (A) is also correct. Statement (A) accurately shows the progression of three sequential periods within the Mesozoic Era from older (Triassic) to younger (Cretaceous). Since the correct option must account for all correct statements, choosing 'Only (B)' improperly excludes the valid sequence in statement (A).

The incorrect option is 3: Only (C)

This option is incorrect on two levels: first, because both statements (A) and (B) are correct sequences and must be included; and second, because statement (C) itself is chronologically flawed. The sequence is given as **Devonian ← Silurian ← Carboniferous**. These are all Periods within the Paleozoic Era. The correct chronological order for these three periods, from oldest to youngest, is: Silurian (443.8 MYA) → Devonian (419.2 MYA) → Carboniferous (358.9 MYA). The provided sequence is inverted and misrepresents the age relationship between the Devonian and Silurian periods relative to the Carboniferous.

The incorrect option is 4: (A), (B) and (C)

This option is incorrect because it claims that all three sequences are correct, but as demonstrated, statement (C) is chronologically inaccurate. The Paleozoic Periods should be ordered, from oldest to youngest, as Silurian, then Devonian, then Carboniferous. The sequence given in (C) is **Devonian ← Silurian ← Carboniferous**, which falsely places the Devonian as older than the Silurian in the indicated directional flow, and also misplaces the Carboniferous. Because sequence (C) contains an error in the ordering of the periods, this option, which includes (C), cannot be the right answer.