Lesson 2: Geologic Time Scale and Earth’s History

-How do rock layers and fossil distributions provide evidence for organizing Earth’s history?

-How is the geologic time scale constructed from multiple lines of scientific evidence?

-What major biological and geological events define transitions between eons, eras, and periods?

-How do scientists determine the relative timing of events before absolute dating is applied?

-Why is Earth’s history best understood through the concept of deep time rather than human time scales?

-How do mass extinctions and evolutionary changes reshape the geologic time scale?

-Geologic time scale

-Deep time

-Eon

-Era

-Period

-Epoch

-Stratigraphy

-Rock strata

-Fossil succession

-Index fossils

-Relative dating

-Absolute dating

HS-ESS1-4 – Use evidence from rock strata and fossil records to construct explanations of Earth’s 4.6-billion-year history and major changes over time.
NGSS Crosscutting Concepts

-Patterns (fossil succession, extinction events, rock layer sequences)

-Cause and Effect (geologic events driving changes in life and environment)

-Stability and Change (Earth systems evolving across deep time)

-Scale, Proportion, and Quantity (understanding billions of years of Earth history)

SBA / PSAT / SAT Connection

-Students will interpret stratigraphic columns and fossil distribution charts to determine relative timing of events.

-Students will analyze geologic timelines to identify patterns of extinction, emergence, and environmental change.

-Students will construct CER explanations using fossil and rock evidence to justify placement of events in Earth’s history.

-Students will evaluate claims about Earth’s history using multiple data sources.

-Students will interpret stratigraphic columns and fossil distribution charts to determine relative timing of events.

-Students will analyze geologic timelines to identify patterns of extinction, emergence, and environmental change.

-Students will construct CER explanations using fossil and rock evidence to justify placement of events in Earth’s history.

-Students will evaluate claims about Earth’s history using multiple data sources.

Students will investigate how scientists reconstruct Earth’s history by analyzing rock layers, fossil evidence, and geologic timelines. Rather than memorizing divisions of time, students will build and justify a simplified geologic time scale using evidence patterns.

Students will examine how major events such as mass extinctions, climate shifts, and evolutionary radiations define transitions in Earth history.

Activities may include:

-Constructing a geologic time scale from fossil and rock evidence sets

-Analyzing stratigraphic columns to determine relative age relationships

-Using fossil succession data to identify patterns of extinction and emergence

-Ordering Earth history events using evidence-based reasoning

-Comparing multiple geologic interpretations and defending conclusions with CER

Purpose

Develop students’ ability to interpret Earth history as an evidence-based system organized through patterns in rock layers and fossil records, emphasizing reasoning over memorization of time divisions.

DOK Level

DOK 3–4 – Strategic Thinking to Extended Reasoning
(integrating multiple data sources to construct and defend Earth history models)

-Understanding Earth’s history in relation to human existence and future environmental change

-Fossil sites and geological formations in national parks and local regions

-Use of geologic time in resource exploration, climate science, and environmental policy

-Earth’s history is short or comparable to human timelines

-Geologic time divisions are arbitrary rather than evidence-based

-All fossils are found in a single layer or time period

-Time is evenly distributed across rock layers

-Evolution happens uniformly rather than in bursts and transitions

-Scaffolded construction of geologic timelines using evidence cards

-Color-coded stratigraphy models and fossil layering visuals

-Chunked datasets for fossil succession analysis

-Guided CER writing with sentence frames and evidence banks

-Peer grouping for timeline construction and justification

-Extension tasks comparing multiple geologic interpretations

-CER explanation: “How is the geologic time scale constructed from evidence?”

-Constructed geologic timeline from fossil/rock data sets

-Stratigraphic column interpretation assessment

-Exit tickets analyzing cause-and-effect relationships in Earth history

-Ordering and justification of major Earth events using evidence

-Fossil distribution data sets

-Rock strata and stratigraphic column diagrams

-Geologic time scale reference charts (for comparison after construction)

-Timeline construction kits or digital tools

-Earth history evidence cards (fossils, events, rock layers)