Geologic Time Scale | CK-12 Foundation - Free Printable

Problem Analysis

The image provided is a study guide for understanding the Geological Time Scale. It includes a table that organizes Earth's history into different divisions (eons, eras, periods, and epochs) and explains key concepts related to the geological time scale. The Concept Check section at the bottom asks three questions that need to be answered based on the information provided in the study guide.

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Concept Check Questions

1. What evidence was used to build the geologic time scale?
2. What is the difference between relative time and absolute time?
3. How is the geologic time scale divided?

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Solution and Explanations

#### Question 1: What evidence was used to build the geologic time scale?
- Answer: Scientists created the geologic time scale based on fossil evidence.
- Explanation: Fossils are the preserved remains or traces of ancient organisms found in rock layers. By studying the types of fossils present in different rock formations, scientists can determine the relative ages of those rocks. Major changes in the fossil record, such as the appearance or disappearance of certain species, mark significant boundaries in the geological time scale.

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#### Question 2: What is the difference between relative time and absolute time?
- Answer:
- Relative time refers to the sequence of events in Earth's history without specific numerical dates. It is based on the principle of superposition (older layers are below younger layers) and the correlation of rock layers across different regions.
- Absolute time (also called radiometric dating) involves determining the exact age of rocks or fossils using radioactive isotopes. This provides numerical ages in years.
- Explanation: Relative time helps establish the order of events but does not provide specific ages. Absolute time, on the other hand, uses techniques like carbon dating or potassium-argon dating to assign actual ages to geological events or rock formations.

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#### Question 3: How is the geologic time scale divided?
- Answer: The geologic time scale is divided into hierarchical units:
1. Eons: The largest divisions of geological time.
2. Eras: Each eon is divided into eras.
3. Periods: Each era is further divided into periods.
4. Epochs: Each period is subdivided into epochs.
- Explanation: The table in the image illustrates this hierarchical organization. For example:
- The Phanerozoic Eon is divided into three eras: Paleozoic, Mesozoic, and Cenozoic.
- The Cenozoic Era is divided into two periods: Tertiary and Quaternary.
- The Quaternary Period is divided into two epochs: Pleistocene and Holocene.
- Each epoch may also be further subdivided into smaller units (e.g., Early, Middle, Late).

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Final Answers

1. Evidence used to build the geologic time scale: Fossil evidence.
2. Difference between relative time and absolute time:
- Relative time: Sequence of events without specific ages.
- Absolute time: Numerical ages determined using radiometric dating.
3. Division of the geologic time scale: Eons → Eras → Periods → Epochs.

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Boxed Final Answers

1. Fossil evidence
2. Relative time: Sequence of events without specific ages; Absolute time: Numerical ages determined using radiometric dating.
3. Eons → Eras → Periods → Epochs

Final Answer:
\boxed{
\begin{aligned}
1. & \text{ Fossil evidence} \\
2. & \text{ Relative time: Sequence of events without specific ages; Absolute time: Numerical ages determined using radiometric dating.} \\
3. & \text{ Eons → Eras → Periods → Epochs}
\end{aligned}
}