Magnetic Variations

 Introduction: A recent 2003 movie 'The Core' proposes that if Earth were to temporarily lose its magnetic field, a wide range of deadly calamities would befall humans and living creatures on Earth. This activity will attempt to place the changes in Earth's magnetic field in an historical context that will hopefully correct many misconceptions about Earth's magnetic field. Earth's magnetic field changes in time, and any map maker will also tell you that our magnetic 'North' pole wanders geographically as well. (see the drawing above and more details at www.geolab.nrcan.gc.ca). During the last 100 years it location has changed by over 1100 kilometers! Although this wandering is rather benign and is only an inconvenience to navigators that still use a magnetic compass, more interesting still, is the fact that the strength of Earth's magnetic field rises and falls over time scales of centuries and millennia. During the last 330 million years, this change has been so extreme that Earth's magnetic field has actually flip-flopped in polarity over 400 times. This activity explores the issue of whether we are approaching another magnetic reversal or not, based on a study of the magnetic intensity variations during the last 800,000 years.

Benchmark:

The graphical display of numbers may help to show patterns such as trends or varying rates of change. Such patterns sometimes can be used to make predictions about the phenomenon being graphed.

Objective:

Students will convert tabulated data into a graph, search for patterns and trends, and make a prediction about future events.

Materials:

Vocabulary:

Magnetic Intensity

Magnetic Polarity

Magnetic Reversal

Magnetic Field

Procedures:

1. Review the basic vocabulary.
2. From the introductory material, discuss Earth's magnetic field and what the students may have heard about its changes over time, and their impacts on life on Earth.
3. Provide time to allow the students to complete the table analysis and plotting activity.
4. Review the answers. Discuss with the students how unsteady Earth's magnetic field has been, and how only the most extreme variation 800,000 years ago actually led to a complete magnetic reversal.
5. Compare the student's answers for the predicted year for when the field strength may vanish based on the most recent decline of 5% per century. Average the estimates together.
6. Be sure to discuss the reasonableness of their answer to Step 5, given that there have been many other declines in field strength during the last 800,000 years which did NOT lead to a reversal.