Geologic Time – Subdivisions of periods In the standard geological time scale, eras are divided into periods. Those periods are further subdivided into what units for finer chronological classification used in stratigraphy and paleontology?

Introduction / Context:
Understanding how the geological time scale is organized is essential for reading maps, correlating rock strata, and interpreting the fossil record. The hierarchy moves from very large spans of time to progressively smaller ones, allowing geoscientists to describe events with appropriate precision.

Given Data / Assumptions:

• Eras are already known to be divided into periods.
• The question asks what the next smaller unit beneath a period is, within the internationally accepted time scale.
• Terms in the options (eons, epochs, stages) are all valid stratigraphic words but refer to different levels.

Concept / Approach:
The standard hierarchy is: Eon > Era > Period > Epoch > Age/Stage. Eons are the largest units (for example, Phanerozoic), eras are subdivisions of eons (for example, Cenozoic), periods subdivide eras (for example, Jurassic), and epochs subdivide periods (for example, Paleocene). Stages (also called ages) are smaller than epochs.

Step-by-Step Solution:
Identify the level in question: a subdivision of a period.Recall the hierarchy: Period → Epoch → Age/Stage.Match the correct term: the unit directly below a period is an epoch.

Verification / Alternative check:
Open any modern geologic time chart: the Jurassic Period contains Early, Middle, and Late Jurassic epochs, each further divided into ages/stages such as Toarcian, Oxfordian, and Tithonian.

Why Other Options Are Wrong:

• eons: higher than eras, not below periods.
• stages: these are below epochs and therefore two levels beneath a period.
• Any of the above: incorrect because only one specific level directly subdivides periods, namely epochs.

Common Pitfalls:
Confusing similar-sounding terms or thinking that stages and epochs are interchangeable. They are not; epochs are larger than stages (ages).

Final Answer:
epochs