Grade Level: 5-8

ACF Lesson Plan: How Was Coal Formed?


Students identify the dates and order of key time frames of geologic history and learn about when and how coal was formed.



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Students will:

  1. familiarize themselves with the names of geologic time frames,
  2. sequence key time frames of geologic history, and
  3. understand the process and timing of the formation of coal.

National Standards:

National Science Education Standards (NSES)

  • Earth and Space Science, 5-8
    • Earth’s history
  • Earth and Space Science, 9-12
    • Geochemical cycles

Time Needed:

One 30-minute class period to build prior knowledge of geologic time Second 45 minute class period for activity.


Discussion Questions:

  • What is geology?
  • What do the terms eon, era, period, and epoch mean?
  • When was coal formed?


  1. Begin by writing the discussion questions on the board or overhead projector. After giving students an opportunity to say what they think the terms refer to, provide them with the following definitions:
    1. Geology: a science that deals with the history of the earth and its life, especially as recorded in rocks.
    2. Eon: a very large division of geologic time usually longer than an era and equal to one billion years.
    3. Era: a large division of geologic time usually shorter than an eon.
    4. Period: a division of geologic time longer than an epoch and included in an era.
    5. Epoch: A unit of geologic time that is a division of a period.

    Additional vocabulary: peat lignite subbituminous bituminous coalification

  2. Write the following names of geologic time frames on index cards: Phanerozoic, Proterozoic, Cenozoic, Mesozoic, Paleozoic, Neoproterozoic, Mesoproterozoic, Paleoproterozoic, Quaternary, Tertiary, Cretaceous, Jurassic, Triassic, Permian, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, Cambrian, Holocene, Pleistocene, Pliocene, Miocene, Oligocene, Eocene, Paleocene, Archean, and Hadean.

  3. Give each student (or pair of students) one (or more) timeframe(s) and provide them with Internet access or encyclopedias to research the answers to the following questions: Is this geologic time frame an eon, era, period, or epoch? How long did this time frame last? When did it take place? Make sure students write the answers to these questions on their index cards, below the name of the time frame. (Note: There are 29 time frames. If there are fewer students in the class, distribute the index cards so that some students will have two cards each. If there are more than 29 students in the class, allow some students to work in pairs.)

  4. After all the students have been able to figure out their time frame identities, see if the students can work as a class to place their time frames in order. Begin by taping the index cards with eons to the top of the blackboard. Be sure to leave plenty of room between them. Next, tape the cards with eras below the correct eons. Place the periods within the appropriate eras. And, finally, tape the epochs under the correct periods. Once they have completed this exercise, place the transparency of the geologic time chart on the overhead projector. Use it to check your class results.

  5. Show the graphic and explanation of the coalification process, How Coal Formed, on your classroom whiteboard. Explain to students that coal, a fossil fuel formed from prehistoric plants that lived hundreds of millions of years ago, was formed during the Paleozoic era. Coal is formed when peat, which is decayed plants and other vegetation, gets buried by sediment. This burial causes the peat to become compacted by pressure and dried out. Continuous heat and pressure causes the peat to break down and chemically change. Certain gases are expelled, making the coal increasingly rich in carbon. The stages of coalification are peat, lignite, subbituminous coal, bituminous coal, to anthracite coal. These are the names given to the increasing carbon-rich ranks of coal.


Have students identify other key geologic events from the time frames they were originally given, and share their findings with the rest of the class. What happened to the earth and the atmosphere during the time frame that facilitated the development of certain rocks, minerals, and fossil fuels.


  1. Encourage students to find out how and when other fossil fuels, such as oil and natural gas, were formed. Have them share their findings with the class, explaining the differences between the formation of oil, natural gas, and coal. They can begin their research with the Department of Energy.
  2. Students can research where the names of the various geologic time frames came from. What do the roots of the words mean? What about the prefixes and suffixes?
  3. The American Geologic Institute has bookmarks with the geologic timescale on the back. It is called the Earth Science Week bookmark (timescale) and can be ordered at or (703) 379-2480.