Geologic Time - Evidence for Evolution

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SWBAT analyze and interpret data for patterns in the fossil record that document the existence, diversity, extinction, and change of life forms throughout the history of life on Earth

Big Idea

Students explore how the geologic time scale is evidence for evolution.


10 minutes

In this section of the lesson I engage students by showing students Four Ways to Understand the Earth's Age, a TEDEd video by Joshua M. Sneideman.   

The Earth is 4.6 billion years old -- but how can humans relate to a number so colossal, and where do we fit on the geologic timeline? Comparing the Earth’s lifetime to one calendar year, events like the extinction of dinosaurs and Columbus setting sail take place relatively recently. This video helps to remind us of our time and place in the universe.  

The objective of showing this video is for students to gain a deeper appreciation of Earth's age compared to us humans and to see how fossils can be used to give us valuable information on how life on Earth has changed throughout time.  Understanding geologic time is significant because it helps us understand the evolution of organisms over time.  (MS-LS4-1: Analyze and interpret data for patterns in the fossil record that document the existence, diversity, extinction, and change of life forms throughout the history of life on Earth under the assumption that natural laws operate today as in the past.) 


As students are watching the video they answer the following questions in their notebook:

1.  Geologically speaking with reference to the entire history of the earth, the dinosaurs went extinct ...

a.  Shortly after the formation of Earth

b.  In the first billion years of Earth's history

c.  In the most recent 2% of the history of Earth

d.  Before the first fish formed

2.  Relative to the percent of time dominating the surface of Earth which organisms have the longest reign?

a.  Dinosaurs

b.  Plants

c.  Prokaryotes

d.  Eukaryotes

d.  Humans

3.  The Earth is ___________ years old.

a.  6,000

b.  46,000,000

d.  4,600,000,000

e.  There is no way to know

4.  100,000 years in the geologic history of Earth would be considered...

a.  Immensely long.

b.  A drop in the bucket.

c.  Half of Earth's history.

d.  An extremely significant amount of time.

5.  Understanding geologic time is significant because it helps us...

a.  Understand human's impact on our environment.

b.  Understand the evolution of organisms over time.

c.  Understand the possibility for life on other planets.

d.  Understand the process of evolution. 

e.  All of the above.

6.  Which organism first dominated Earth?

a.  Dinosaurs

b.  Insects

c.  Plants

d.  Fish

e.  Bacteria

After students have answered the questions above I have students answer and discuss the following question in their cooperative groups:

How does understanding the past help us understand the present?

This question is meant to link the fossil record, evolution, and present day organisms.


20 minutes

In this section of the lesson students complete a module titled Understanding Geologic Time courtesy of the University of California Museum of Paleontology.  

Understanding Geologic Time is an informational tour in which students gain a basic understanding of geologic time, the evidence for events in Earth’s history, relative and absolute dating techniques, and the significance of the Geologic Time Scale. (MS-LS4-1-Analyze and interpret data for patterns in the fossil record that document the existence, diversity, extinction, and change of life forms throughout the history of life on Earth under the assumption that natural laws operate today as in the past.) 

Learning Objectives:

  • That the Earth has a very long history;
  • About some of the events that have taken place during Earth's history;
  • How scientists use the Law of Superposition to determine the relative age of rocks and fossils;
  • How scientists use radiometric dating to determine the absolute age of rocks and fossils;
  • That the Geologic Time Scale is a vertical timeline representing the history of the Earth; and
  • How the Geologic Time Scale is arranged into periods of time based on major changes in biodiversity.


  • Students take Geologic Time Pre/Post Test  to assess their background knowledge on topic (Students take test before and after module)
  • Students work in teams of two per computer to allow students to read and share ideas with one another as they proceed.
  • Students complete Scavenger Hunt as they proceed through module
  • Students take Geologic Time Pre/Post Test which assesses how much they have learned.

Teacher Note:  Just as the video in the Engage part of lesson used analogies to explain the time scale, this module uses analogies to communicate the idea of how old earth is relative to human events.  


10 minutes

In this section of lesson students read an article titled Life and the Geologic Time Scale from cK-12. They use the Writing in the Margins strategy to interact with text

Writing in the margins engages readers in the reading task and allows them to document their thinking while reading. Both writing in the margins and drawing in the margins engages students in actively thinking about the texts they read. The power of this strategy is not the actual act of writing and drawing in the margins; instead, it is the thinking processes that students must undergo in order to produce such ideas. 

Students use the Summarize strategy, which is explained in my reflection. One note - summary writing does require instruction for students, so if students aren't accustomed to summary writing another choice for a strategy might be guided note taking. This is also explained in my reflection.

Once students have read the article, they are required to answer the following text-dependent questions. Make sure students remember (circulate, remind) that they took summary notes so that they have the information needed to respond to these questions. Otherwise building their use of summary notes lacks purpose and meaning. (RST.6-8.1 - Cite specific textual evidence to support analysis of science and technical texts, attending to the precise details of explanations or descriptions.) 


  1. Why do we not know exactly when life first evolved on Earth?
  2. When did life become abundant?
  3. Where do humans appear in this graphic? Is that where you would expect them to be? 


15 minutes

Students now analyze the data found in the Kentucky Geological Survey Geologic Time Scale. (SP4-Analyzing and Interpreting Data/CCC Patterns - Graphs, charts, and images can be used to identify patterns in data.) 

Students use data to answer the following questions:

1.  Categorize all events that occurred in each of the four eras.

2.  How many millions of years pass between earth's formation and the first origins of life?

3.  When did bacteria first appear?

4.  When did the first cells with a nucleus appear?

5..  When did the first mammals appear? 

6.  What evidence do you have to support the claim found below:

"The Cambrian explosion, or less commonly Cambrian radiation, was the relatively short evolutionary event, beginning around 542 millions years ago in the Cambrian period during which most major animal phyla appeared, as indicated by the fossil record."

7.  What evidence can you use to support the claim that humans have been on earth for a very small amount of time?

Constructed Response:

Using evidence from today's activities, explain how the Geologic Time Scale can be used to understand the evolution of organisms over time. (WHST.6-8.2 - Write informative/explanatory texts to examine a topic and convey ideas, concepts, and information through the selection, organization, and analysis of relevant content.)