Learning Goals

How to teach absolute dating, context for use

Time factors of millions and billions of years is difficult even for adults to comprehend. Keep in mind that extinction is forever. Pretty obvious that the dike came after the rocks it cuts through, right? Students should have the skill to set up a data table and a graph, however, if you want to use this activity with students that have not, you can provide them a template with that information.

From the chart, which methods are best for older materials? Based on the Rule of Superposition, certain organisms clearly lived before others, during certain geologic times. During each trial, students record the number of radioactive parent isotopes and record this in a data table. By correlating fossils from various parts of the world, scientists are able to give relative ages to particular strata. This rate of decay is called a half-life.

Lesson Introduction

In a way this field, called geochronology, is some of the purest detective work earth scientists do. Once this is done, students have some post questions they are given that they should record in their science notebook. This would also mean that fossils found in the deepest layer of rocks in an area would represent the oldest forms of life in that particular rock formation.


Radioactive Dating Looking at Half-Lives Using M&Ms

Radioactive Dating Looking at Half-Lives Using M&Ms

Each radioactive isotope works best for particular applications. After students take a few seconds to track their scores, we usually wrap up in a similar way. Say for example that a volcanic dike, or a fault, cuts across several sedimentary layers, or maybe through another volcanic rock type.

Absolute Dating
Radiometric dating

They then see some new vocabulary and get to practice applying it before closing out for the day. Name three organisms represented that probably could not be used as index fossils and explain why. Spread the cards with the nonsense syllables on the table and determine the correct sequence of the eight cards by comparing letters that are common to individual cards and, therefore, overlap. Students will understand how scientists use half-lives to date the age of rocks. Once this info is calculated, students create a graph comparing the class average of parent isotopes to the number of half-lives.

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This activity would also be easy to adapt when talking about half-lives within a chemistry course. Use this information to sequence the cards in a vertical stack of fossils in rock strata. It is the concept, regardless of shape, sediments are always deposited in flat layers. Relative age dating also means paying attention to crosscutting relationships.

New information needed to be introduced with parent and daughter isotopes. Sedimentary rocks in particular are notoriously radioactive-free zones. No bones about it, fossils are important age markers. Once all groups data is on the table, you can calculate the average for each run and determine a class average.

  • Sequence the remaining cards by using the same process.
  • Each card represents a particular rock layer with a collection of fossils that are found in that particular rock stratum.
  • Locally, physical characteristics of rocks can be compared and correlated.

Parent isotopes are represented by the M side up radioactive. Specific rock formations are indicative of a particular type of environment existing when the rock was being formed. Find a rock layer that has at least one of the fossils you found in the oldest rock layer.


This is the first, and one of the most important, lessons in the new unit. Not all rocks have radioactive elements. The study of fossils and the exploration of what they tell scientists about past climates and environments on Earth can be an interesting study for students of all ages.

Students graph, post questions, and data table will be looked at. All of the fossils represented would be found in sedimentary rocks of marine origin. Additionally, they're mostly organized to get increasingly more difficult and increase in complexity, which is why the harder questions tend to come toward the end. Take students on a neighborhood walk and see what you can observe about age dates around you. How do scientists actually know these ages?

  1. With absolute age dating, you get a real age in actual years.
  2. If certain fossils are typically found only in a particular rock unit and are found in many places worldwide, they may be useful as index or guide fossils in determining the age of undated strata.
  3. Students should recognize each time the number should go down by appx half.
  4. This rule is common sense, but it serves as a powerful reference point.

Half-life simply means the amount of time it takes for half of a remaining particular isotope to decay to a daughter product. This was a new activity we implemented last tear. Carefully examine the second set of cards which have sketches of fossils on them. This also means that fossils found in the lowest levels in a sequence of layered rocks represent the oldest record of life there.

We use a combination of strategies active voting, cold calling, popsicle sticks, volunteers to go over the responses, where students correct their work and ask any clarifying questions. Daughter isotopes are represented by the M side down stable. That also means if the layers are not flat, something has happened to them. Which fossil organisms could possibly be used as index fossils?

Sequencing the rock layers will show students how paleontologists use fossils to give relative dates to rock strata. After students grade their exit tickets, online dating sites for they usually pass them in so that I can analyze them and track their exit ticket scores on a unit Exit Ticket Tracker. Then students take the class data and create a graph comparing the number of parent isotopes to the number of half-lives.

Eighth grade Lesson Introduction To Relative Dating

So geochronolgists just measure the ratio of the remaining parent atom to the amount of daughter and voila, they know how long the molecule has been hanging out decaying. On a larger scale, even between continents, fossil evidence can help in correlating rock layers. For example, most limestones represent marine environments, whereas, sandstones with ripple marks might indicate a shoreline habitat or a riverbed. Once all groups finish, soundcloud dating each group records their info on the class decay table on the board and we calculate the averages of the class. Students should have some prior knowledge of rocks and how they are dated.

Teaching about Earth's history is a challenge for all teachers. This will enable your teacher to quickly check whether you have the correct sequence. Big Idea Students discuss the differences between relative and absolute dating, and figure out how geologists date rock layers in this introductory lesson. If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric absolute age dating as well.

State the Law of Superposition and explain how this activity illustrates this law. This method works because some unstable radioactive isotopes of some elements decay at a known rate into daughter products. Are there repairs or cracks in the sidewalk that came after the sidewalk was built? Students will be able to explain what a half-life of a rock is.

Absolute Dating - Lessons - Tes Teach

But the most accurate forms of absolute age dating are radiometric methods. In this activity, students gain a better understanding of radioactive dating and half-lives. Summary In this activity, students gain a better understanding of radioactive dating and half-lives. In what kinds of rocks might you find the fossils from this activity? By using this information from rock formations in various parts of the world and correlating the studies, scientists have been able to establish the geologic time scale.

Geologic Age Dating Explained

Absolute dating Science Learning Hub

Home Professional Learning. This is called relative dating. Scientific measurements such as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age.

Context for Use

Introduction To Relative Dating

Once students are in their groups, with supplies, and general directions are given, they are on their own for doing their runs. You might have noticed that many of the oldest age dates come from a mineral called zircon. Earth Science Kane Koller. In this activity, students begin a sequencing activity with familiar items - letters written on cards. There are a couple catches, of course.

Learning Goals

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