Geologic Time Scale – Smallest formal subdivision In standard stratigraphic hierarchy used by geologists worldwide, what is the smallest commonly used formal unit of geologic time?

Introduction / Context:
The geological time scale organizes Earth history into nested units for global correlation of rocks and fossils. Knowing the order and smallest commonly used unit helps in reading stratigraphic charts and scientific papers.

Given Data / Assumptions:

• We refer to internationally recognized chronostratigraphic/ geochronologic units.
• Terminology pairs: eon/eonothem, era/erathem, period/system, epoch/series, age/stage.
• We seek the smallest formal level widely applied.

Concept / Approach:
The hierarchy is: Eon > Era > Period > Epoch > Age/Stage. In time terms, age is the smallest, and in rock terms the corresponding unit is the stage. Many textbooks and questions reference “stage” as the smallest formal subdivision used for detailed correlation (for example, Oxfordian Stage, Tithonian Stage).

Step-by-Step Solution:
Recall the full hierarchy.Identify the smallest level: age (time) / stage (rock record).Choose “stage” as the named unit in the options corresponding to the smallest subdivision.

Verification / Alternative check:
International Commission on Stratigraphy charts list stages as the most finely resolved formal units (many further subdivide informally into zones, but zones are not formal global units).

Why Other Options Are Wrong:

• eon, eras, periods: progressively larger, not smaller.

Common Pitfalls:
Confusing informal biozones or lithozones with formal time units; those are not universally formalized like stages/ages.

Final Answer:
stage