# Geologic Time in Your Region

Part of the Geology Merit Badge Digital Resource Guide: [Introduction & Overview](https://merit-badge.university/merit-badges/geology/guide/index.md)

*4. Earth History*

> **4d1.** Create a chart showing suggested geological eras and periods. Determine which period the rocks in your region might have been formed.

Human history feels long until geology enters the room. In geology, a road cut might expose layers that formed hundreds of millions of years before the first humans appeared. This requirement asks you to place your local rocks into that deep-time framework.

## Build the Timeline First

A useful chart should include the major eras and the periods within them. You do not need every tiny subdivision. The point is to understand order and scale.

A simple chart often includes:

- **Precambrian**
- **Paleozoic Era**
- **Mesozoic Era**
- **Cenozoic Era**

Within those eras, include the major periods your counselor expects you to know or that appear on the maps and legends for your region.

## Then Place Your Region's Rocks

Use your local geologic map, state survey, or counselor-approved source to ask:

- What formation names appear in my area?
- What period or era are those formations assigned to?
- Are all the local rocks the same age, or do several ages appear?

If your region has mostly sedimentary rocks from one period, that suggests one major environment may have dominated for a long time. If your area includes rocks from many ages, the history may be much more complex.

![Vertical geologic timescale aligned with a simplified regional rock column and matching periods](https://ik.imagekit.io/doulacoop/tr:w-800/mbu-assets/merit-badges/geology/guide/geologic-timescale-and-local-rocks?v=3ec75450)

> **Tip**
>
> Tie this page back to Req 3. If you already used a geologic map there, check the legend again and look for the period labels attached to each unit.

## Official Resources

Video: [The Geological Timescale (video)](https://www.youtube.com/watch?v=5Prp5iYFu4w)

Next you will add the driving force behind many of Earth's biggest changes: moving tectonic plates.

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- Previous: [Deep Time and Ancient Worlds](https://merit-badge.university/merit-badges/geology/guide/req4d/index.md)
- Next: [Plate Tectonics](https://merit-badge.university/merit-badges/geology/guide/req4d2/index.md)