Summary

In this lesson, students will answer questions about rocks and minerals while listening to a podcast. Additional information is provided to guide students toward understanding the nature of radioactive half-lives. how the study of rocks and minerals helps scientists make conclusions about how and when the earth was formed.

Grade Level

High school

NGSS Alignment

This activity will help prepare your students to meet the performance expectations using the following practices:

• HS-PS1-8: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay.
• HS-ESS1-6: Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of Earth’s formation and early history.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Developing and Using Models

Objectives

By the end of this lesson, students should be able to:

• Explain how the study of rocks and minerals helps scientists make conclusions about how and when the earth was formed.
• Evaluate and create models to quantitatively represent nuclear decay using half-life concepts.

Chemistry Topics

This lesson supports students’ understanding of:

• Radioactive isotopes
• Half-lives

Time

Teacher Preparation: ~5 minutes (allow 35 additional minutes to listen to the podcast)

Lesson:

• Part 1: 50-60 minutes
• Part 2: 20 minutes (or given as homework)

Materials

• Podcast Episode: Zircon: How this tiny, ancient mineral is upending what scientists believed about early Earth (33 minutes, 50 seconds)
• Student handout

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• The focus of this lesson is that scientists can study a very stable and durable mineral, zircon, to learn about the age and conditions of the early earth. The strength of the bonds makes zircon crystals (grains) able to remain intact even when the rock that contains them cycles back into the molten magma inside the earth and most other compounds are broken down. This allows radioactive impurities inside zircon crystals to remain trapped in the lattice. As some of the radioactive impurities have very long half-lives, they can be used to date substances as old as the earth.
• Pre-requisite knowledge for this activity:
  • Isotope notations showing element symbol, atomic number, and mass number
  • Basic introduction to the process of nuclear decay
• You can access the podcast via the website or any podcast platform listed there:
  • Zircon: How this tiny, ancient mineral is upending what scientists believed about early Earth (33 minutes, 50 seconds)
  • The podcast discusses how a mineral, zircon, survives throughout the rock cycle and how it can be used to determine ages of rocks and other geologic formations.
  • It is recommended that students be allowed to listen independently to the podcast while answering questions so they can pause, slow down, or repeat segments as needed.
• Page 1 of the student handout (warm-up questions and notes) can be done collaboratively or as a teacher-led activity, as students may have last seen the rock cycle in either middle school or in a high school earth science class. The warm-up questions provide prompts for students to think about what they may remember about the rock cycle.
• After the warm-up, briefly review the following points to give context to the information in the podcast. Students should take notes in their “Notes about the Rock Cycle” section.
  • Deep inside the earth a giant mixture of elements and compounds in liquid form is always moving.
  • Minerals are pure substances with a definite chemical composition that form when portions of the liquid mixture cool.
  • Small fragments of many minerals that solidify from the liquid mixture can form a solid mixture that we call a rock.
  • Copy or project the diagram from page one of the student activity onto the front board. Refer to this diagram as you discuss each of the points below.
    • When portions of this mixture cool, either inside the earth (from magma) or on the earth’s crust (from lava), igneous rocks are formed. The mixture may contain elements or compounds that have been there since the earth formed and it may contain elements or compounds that have gone through portions of the rock cycle.
    • Igneous rocks may cycle back into the liquid portion of earth or may stay on the earth’s surface and get weathered and eroded.
    • Sedimentary rocks form when lots of fragments of other rocks get compressed into new mixtures and typically form layers. These rocks may cycle back into the liquid portion of earth or may stay on the earth’s surface and get weathered and eroded again.
    • Metamorphic rocks form when other rocks are subjected to heat and pressure, changing the nature and composition of the original rocks. These rocks may cycle back into the liquid portion of earth or may stay on the earth’s surface and get weathered and eroded.
    • When rocks cycle back into the liquid phase, no trace of the original rock will remain because the rock was just a mixture of minerals. Minerals, however, may survive certain cycles if the varying conditions don’t cause their bonds to break.
• Part 1: Students should complete the active listening section during class. The podcast is ~34 minutes long. (There is a “Tiny Show and Tell” segment at the end that is unrelated to the major topic. The teacher should decide and tell the students whether they should listen to this or not. It is only the last ~2-3 minutes.)
  • Students are directed to pause the podcast at the 8:46 mark, so they can read some information and answer associated questions about the nature of radioactive decay and half-life. This will help them to understand the remaining portion of the podcast where basic knowledge of these topics is assumed.
  • The teacher may guide students through questions 5-7, have students work in pairs and then report out, or suggest that students work through the information and questions on their own before reviewing as a class. Whichever method is used, it is recommended that the teacher review answers to these questions before students continue with the podcast.
• Part 2: Conceptual questions about half-life can be completed in class or as homework and reviewed during the next class session.
• An Answer Key document is available for teacher reference.

Related resources in AACT library:

• Activity: Radioactive Decay and Seafloor Data: Radiometric data is used to date rock samples and interpret seafloor data.
• Activity: Radioactive Decay and Peat Bogs: Students apply understanding of radioactive decay and half-life to study a peat bog.
• Activity: Using Stable Isotopes to Determine Material Origin: A set of activities review the nature of isotopes and average atomic mass, then use isotope ratio measurements in a hair sample to interpret locations that a person has traveled.