In the geological time scale, eras are divided into which smaller units?

Introduction / Context:
Geology uses a hierarchical time scale to describe the long history of Earth. Understanding this structure is helpful not only in geology but also in competitive exams where basic scientific literacy is tested. This question asks how eras fit into the geological time scale and specifically which smaller units are used to subdivide an era.

Given Data / Assumptions:

• The focus is on the geological time scale.
• The unit we start from is an era, not an eon.
• The options list ages, epochs, periods, or a combination of periods and epochs.

Concept / Approach:
The commonly accepted hierarchy in geological time is: eon, era, period, epoch, and age. This means that an eon is divided into eras, an era is divided into periods, each period is divided into epochs, and epochs may be further divided into ages. Therefore, when the question asks how an era is divided, the correct answer must include periods and, indirectly, epochs which are nested within those periods.

Step by Step Solution:
Step 1: Recall the order of units from largest to smallest in geological time. Step 2: Identify that eon is larger than era. Step 3: Note that an era contains several periods, such as the Cenozoic era containing the Paleogene, Neogene, and Quaternary periods. Step 4: Recognize that each period may then be divided into epochs, for example the Quaternary period includes the Pleistocene and Holocene epochs. Step 5: Thus, eras are divided into periods and those periods are further subdivided into epochs, so the most accurate option is periods and epochs.

Verification / Alternative check:
You can verify by looking at any standard geological time scale chart, where eras such as Paleozoic, Mesozoic, and Cenozoic are clearly split into well named periods. Within the Cenozoic era, for instance, you see periods like Paleogene and Neogene, and each of those is further broken down into epochs. Ages generally appear as smaller divisions at the bottom of the hierarchy, not directly next to eras. This confirms the combined answer.

Why Other Options Are Wrong:
Ages only: Ages are the smallest commonly used units and do not directly divide eras, so this option is not correct.
Epochs only: Epochs exist within periods, not directly under eras, so saying eras are divided only into epochs ignores the period level.
Periods only: This is partially true but incomplete, because periods themselves are subdivided into epochs, and the question points to both levels of smaller units.

Common Pitfalls:
A common mistake is to remember only some of the hierarchy and assume that eras move directly to epochs, skipping periods. Another issue is general confusion between similar sounding terms, especially when students memorize them without context. Visualizing the time scale as a tree from large to small units can help fix the correct order in memory.

Final Answer:
In the geological time scale, eras are divided into periods and epochs.