Description
What our Geologic Time lesson plan includes
Lesson Objectives and Overview: Geologic Time is an excellent lesson to help students understand how scientists determine the age of the earth. Students will define geologic time, identify eras and periods along with their major events, and explain the length of geological time relative to shorter time periods. This lesson is for students in 4th grade, 5th grade, and 6th grade.
Classroom Procedure
Every lesson plan provides you with a classroom procedure page that outlines a step-by-step guide to follow. You do not have to follow the guide exactly. The guide helps you organize the lesson and details when to hand out worksheets. It also lists information in the yellow box that you might find useful. You will find the lesson objectives, state standards, and number of class sessions the lesson should take to complete in this area. In addition, it describes the supplies you will need as well as what and how you need to prepare beforehand. For this lesson, you will need construction paper, rulers, colored pencils or markers, scissors, tape, and glue. Students will also need access to the internet.
Options for Lesson
Refer to the “Options for Lesson” section for suggestions of ideas and activities that you could incorporate into the lesson plan if you have time. If you want, students could work alone or in larger groups for the activity. Another idea is to split the class into four groups. Each one could research one era or eon and present what they discover to the class. Depending on the size of class, you could assign each student a time-period to research. Another suggestion is to invite a geologist or paleontologist to speak to the class about geologic time. As another activity, students could create a timeline of their life and identify specific periods, such as infancy, toddler, school-age, etc.
Teacher Notes
The paragraph on this page gives you a little more information on the lesson overall and describes what you may want to focus your teaching on. It suggests having students memorize the order of events depending on their age or level of ability. The blank lines are available for you to write out any thoughts or ideas you have as you prepare.
GEOLOGIC TIME LESSON PLAN CONTENT PAGES
What Is Geologic Time?
The Geologic Time lesson plan contains three pages of content. 1What is the one thing everyone is born with and all of us have the same amount of each day? Time, of course! Have you ever wondered why, when you’re doing something you genuinely enjoy, time seems to pass very quickly? Or, if you have to do homework or chores that you don’t like, it seems like time moves very slowly? It doesn’t really do either; it just seems that way. That is why it’s hard to imagine what it was like a billion years ago.
Try this simple experiment. Use a timer and see how long you can hold your breath. It may seem like a lot of time passes, but when you look at a timer, you realize it’s way less than you thought. That is what geologic time is like. The earth is approximately 4.6 billion years old. Comparing the earth’s age with the age of the universe, many scientists believe the universe is approximately 13.6 billion years old. Others think it may be much older—around 26 billion years. Just like in the experiment where you held your breath, it may seem like a long time, but it wasn’t. The earth has been around for a relatively short time compared to the universe.
Geologic time is the entire span of the earth’s history, from its formation to the present day. To help us understand geologic time, scientists have organized it into units. The scale is based on the rock record and significant events in Earth’s history, including geological changes and the evolution of life, as documented in the fossil record.
Eons, Periods, Epochs, and Ages
4Eons are the most extended time periods, about 500 million years or more. There is, however, the Precambrian Super Eon that spans nearly 4 billion years, which is 88% of Earth’s history! It is divided into three eons (Hadean, Archean, and Proterozoic) due to its considerable length. The American Geosciences Institute and the United States Geological Survey then categorize geologic time into three major eras following the Precambrian Super Eon. An era is a major division of the earth’s history. Eras last hundreds of millions of years. Each one is separated by the changes in the types of life and the geological changes that occurred during that time.
Next, scientists further divide geologic time into other descriptive categories. These are periods and epochs. A period in this context is a unit of geologic time representing a span of tens to hundreds of millions of years during which specific rock systems formed and significant geological events occurred. An epoch represents a span of time that typically lasts several million years. During this time, there is substantial evidence of changes in the earth’s rock record.
Technically, within an epoch, you can divide geologic time into ages. An age is the smallest formal unit of time used to mark relatively “short” intervals, just hundreds of thousands of years. However, sometimes the word “age” is used informally to emphasize main life forms from a certain era or period, such as the “Age of Reptiles”—the nickname for the Mesozoic Era. In these cases, age is not a measure of geologic time.
How to Keep Track
You may wonder, given how long ago these changes occurred, how scientists determine when one period ends or an epoch begins, and so on. The geologic time of the earth has been determined using methods that assess the age of rocks, fossils, and other materials that comprise the earth. Geologists use radioactivity to discover the age of substances found throughout the earth. They measure the amount of certain radioactive elements in a rock, such as uranium or lead. The radioactive elements change over time, and this helps geologists determine the approximate age of the rock. If the rock includes fossils, this helps identify what appeared during various time periods of the earth’s existence.
It is important to remember that geologic time intervals overlap, and the exact dating of a fossil or rock is not always precise. Scientists sometimes disagree over when a span begins or ends exactly. The order of geologic time spans from longest to shortest is eon, era, period, and epoch.
The Purpose of the GTS
This all may sound very complicated! Just think of how we divide time. We divide time into seconds, minutes, hours, days, weeks, months, and so on. Geologic time works similarly, but with much longer time spans. What is so unique about time spans that scientists need so many divisions and categories? Great question! Earth’s history is so vast that smaller units are needed to mark major changes in rocks, climate, and life. The eras following the Precambrian Super Eon are part of the Phanerozoic Eon—Paleozoic, Mesozoic, and Cenozoic.
The earth is currently in the Cenozoic Era, which has lasted for approximately 65 million years to date. The era is sometimes known as the “Age of Mammals,” and the Quaternary Period within the era is known as the “Age of Man.” As you can see, the earth is ancient, yet not nearly as old as the universe itself. Human civilization has existed for only a fraction of geological time. Geologic time is broken down into eons, eras, periods, and epochs. Scientists use this system to help them identify the events that have occurred on Earth, including the first appearance of single-celled organisms and the emergence of mammals and humans.
GEOLOGIC TIME LESSON PLAN WORKSHEETS
The Geologic Time lesson plan includes two worksheets: an activity worksheet and a practice worksheet. Each one will reinforce students’ comprehension of lesson material in different ways and help them demonstrate when they learned. Use the guidelines on the classroom procedure page to determine when to distribute each worksheet to the class.
ERA TIMELINE ACTIVITY WORKSHEET
Students will work with a partner for this activity. They will choose one era and create a pictorial timeline chart using their own drawings or images taken from the internet. The worksheet lays out the steps for them to follow to complete the assignment.
GEOLOGIC TIME PRACTICE WORKSHEET
The practice worksheet requires students to answer 10 prompts based on what they learned in the lesson.
Worksheet Answer Keys
At the end of the lesson plan document, there is an answer key for the practice worksheet. All the correct answers are in red to make it easy for you to compare them with students’ responses. If you choose to administer the lesson pages to your students via PDF, you will need to save a new file that omits this page. Otherwise, you can simply print out the applicable pages and keep this as reference for yourself when grading assignments.
