This website is no longer actively maintained
Some material and features may be unavailable
June 22nd, 2010
Life As We Know It
Lesson Overview

For a Printer-Friendly version of this lesson, click here: (PDF) (RTF)

Grade Level: 9-12

Time Allotment: 3 45-minute class periods

Overview: Where did life on Earth come from, and how did it become what it is today?  Students will explore the answer to that question in this lesson on evolution.  The lesson begins with an overview of the history of evolutionary theory, and then takes students on a tour of three billion years of life on the planet using an online interactive timeline.  Students will learn, using video segments from the PBS series The Human Spark, how modern humans evolved from our earliest primate ancestors.  As a culminating activity, students will examine some of the factors that continue to contribute to the evolution of new species and life on Earth.

Media Resources:

The Human Spark, selected segments

Links in the Evolutionary Chain

An exploration of some of the different characteristics that distinguish different branches of the hominid “family tree,” such as brain and face size, ability to make tools, and location.

Human Nature

A look at the ways in which monkeys and apes are similar to humans, not just biologically but mentally and socially


Evolution: Change: Deep Time

This interactive timeline from the PBS series NOVA’s extensive Evolution website shows geological and biological milestones on Earth starting 4.5 billion years ago.


Deep Time Milestones Student Organizer (PDF) (RTF)

Deep Time Milestones Student Organizer Answer Key (PDF) (RTF)


Students will be able to:

  • Explain the history of evolutionary theory, and the theory of natural selection as developed by Charles Darwin;
  • Identify milestones in the evolution of life on Earth over the past 3.8 billion years;
  • Compare and contrast characteristics of modern humans with early human and primate ancestors, and analyze how this may have affected our evolutionary path;
  • Define the terms genetic drift, speciation, biodiversity, and extinction, and discuss how these factors contribute to the evolution of species.


National Science Education Standards

Life Science

Content Standard C


[See Unifying Concepts and Processes]

  • Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuring selection by the environment of those offspring better able to survive and leave offspring.
  • The great diversity of organisms is the result of more than 3.5 billion years of evolution that has filled every available niche with life forms.
  • Natural selection and its evolutionary consequences provide a scientific explanation for the fossil record of ancient life forms, as well as for the striking molecular similarities observed among the diverse species of living organisms.
  • The millions of different species of plants, animals, and microorganisms that live on earth today are related by descent from common ancestors.
  • Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.

Before the Lesson/Prep for Teachers

Prior to teaching this lesson, you will need to:

Preview all of the video segments and websites used in the lesson.

Download the video clips used in the lesson to your classroom computer(s) or prepare to watch them using your classroom’s Internet connection.

Bookmark all websites that you plan to use in the lesson on each computer in your classroom. Using a social bookmarking tool such as or diigo ( (or an online bookmarking utility such as portaportal) will allow you to organize all the links in a central location.

Prepare all classroom materials. Print out and make copies of the “Deep Time Milestones” student organizer for each student in your class.

a. Prepare for the Gallery Walk activity by writing the following questions at the top of flip chart pages or large pieces of paper (one question per page): Genetic Drift: When a new population is established by a very small number of individuals from a larger population there tends to be a lack of genetic variation.  This is called the Founder Effect.  What are some of the disadvantages to this lack of variation?

b. Speciation: It is speculated that the Homo heidelbergensis population split – some moving to Europe and evolving into Neanderthals, others remaining in Africa to become Homo sapiens.  What type of speciation is this, and what effect did it have on the human population?

c. Biodiversity: During the Cretaceous period, biodiversity levels were high.  Mammals, dinosaurs, birds, marine creatures, and plant life flourished all over the planet.  Then, a massive meteor impact 65 million years ago wiped out 60 – 80% of all species on the planet.  Why did some survive and not others?

d. Extinction: The most recent large scale extinction event, the Holocene, includes many plants and animals but most notably large mammals and rainforest species.  Many believe that humans are largely responsible for these extinctions.  Do you feel that humans have contributed to extinctions over the past 10,000 years?  Why or why not?

e. Natural selection: Survival isn’t always based on physical fitness, but on the way our brains work.  Things like social skills, language, and technological capability may have been what allowed us to dominate over our ancestors.  What skills do we have that our earlier or primate ancestors didn’t, and why might they have been passed down to younger generations?

Post the flip chart pages around the room prior to the Culminating Activity.  If you are not familiar with conducting a “Gallery Walk” in your classroom, review the procedure at the “How to Use Gallery Walk?” Web page.

Proceed to Lesson Activities.

Inside This Lesson

Produced by THIRTEEN    ©2021 Educational Broadcasting Corporation. All rights reserved.