The Earth's Shells - Thicknesses and Densities

Initial Publication Date: October 18, 2004 | Reviewed: November 1, 2012


This module explores the combination of densities and shell thicknesses that produce an aggregate density of the Earth of 5.5 g/cm3. Students recreate spreadsheets shown in the Powerpoint module on their own with formulas that answer various pieces of the overall question. This is the fifth module in a series of six that examine the density of planets and rocks.

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Learning Goals

  • Gain knowledge of the weighted average and how each part of the Earth contributes to the total average density.
  • Gain an understanding of the integral operation as a way of summing a large number of individual contributions.

Context for Use

This module was designed to be used in an undergraduate mathematical geology class where students are asked to look at geological questions mathematically and may spend more time on the math than on the geology.

Description and Teaching Materials

This module is one of several developed by Dr. Vacher. The module presentation can be found at

The Powerpoint file is considered to be the student version. There is also an instructor's version that has active spreadsheets in it. There are instructions for requesting this version on the website.

Teaching Notes and Tips

These modules were developed as essentially self-paced, take-home lab assignments. Students are supposed to work through the modules, slide by slide, building their own worksheets as they go along, taking note of instructions and prompts, hints, and queries.

Students must have access to computers equipped with a spreadsheet program such as Excel.


The easiest way to test student work on this module is to ask students to hand in a copy of their worksheets starting with a different set of input data. The module also ends with homework assignment questions.

References and Resources