# Sea Floor Spreading I

#### Summary

In this introductory Excel tutorial, students use Excel to explore the geodynamics Model equation for ocean depth around a sea-floor spreading center (see David T Sandwell or Turcotte and Schubert, 2002). The activity is primarily an introductory tutorial on Excel for students with no prior Excel experience. The use of the equation relating ocean floor depth to sea floor spreading rate and distance from spreading center provides a geoscience context. Activity II (see teaching notes and tips below) is a follow-up activity that has students use Excel to graphically compare the model predictions to observations from several North Atlantic cross-sections.

## Learning Goals

- input numbers and labels, format fonts, numbers, alignment, and cell widths
- use simple equations and copy these to other cells to generate a table from a mathematical formula (analytical model)
- learn about fixed and variable cell references in Excel equations
- make and format graphs with multiple curves
- learn how ocean topography is predicted (i.e. modeled) to vary with sea floor spreading rates, mantle density and mantle temperatures.

## Context for Use

## Teaching Materials

We provide the following resources with this module:

- Activity Sheet (Acrobat (PDF) 550kB Sep8 03)
- Answers Document (Excel 37kB Apr3 04) with several sheets representing different levels of completion. These Excel documents can be used for the following purposes:
- Introducing concepts and ideas in an interactive lecture.
- Making transparencies or Power Point slides.
- Checking student results.

## Teaching Notes and Tips

This activity will take students about two hours to complete. Students should be able to work through this activity at home or in a computer lab will no supervision. Students more familiar with Excel can work through this activity more quickly.

In a follow-up activity (Sea Floor Spreading II), students compare actual data from Topex satellite measurements to the model predictions of how sea floor spreading rates influence ocean topography. North Atlantic cross-sections at 30° N, 40° N , and 50° N latitude are provided as is information on how to retrieve Topex elevation data from any location globally.

## Assessment

Grading the completed activity sheet provided can be used as an assessment of student understanding. The future success of students on other Excel related activities is also another useful assessment tool.

A link to an Excel Answers Document is provided above with several sheets representing different levels of completion for this activity. This can help instructors:

- assess student success for this acivity;
- answer student questions that come up;
- quickly familiarize themselves with the activity.

**Figure 1.** Predicted (modeled) ocean topography for three different spreading rates, U.

**Figure 2.** Predicted ocean topography for C=0.11, 0.10, and 0.15 (Exp 1,2, and 3) corresponding to base values of mantle density and temperature of:

3.3 g/cc and 1580 K Exp 1 (control)

4.3 g/cc and 1580 K Exp 2 (30% increase in mantle density)

3.3 g/cc and 2050 K Exp 3 (30% increase in mantle temperature)

{See Brief overview of Ocean Depth/Sea Floor Spreading Model for a description of the model equation, c, and how it relates to mantle temperature and density.}

## References and Resources

- Brief overview of Ocean Depth/Sea Floor Spreading Model
- Turcotte, D.L. and G. Schubert (2002). Geodynamics, (2nd Ed.). Cambridge University Press.
- On-line paper by David T Sandwell (more info)
- This link is a good generic resource for an introduction to Excel
- A follow-up activity, Sea Floor Spreading II
- Resources Graphing Tutorial: Graphing with Excel (more info) : Data input into cells, Creating a scatter plot and line graph. Advanced: Bar graphs and histograms, Importing text files, Final formatting, Regression lines, Superimposing graphs, Descriptive statistics, Selecting data for display