1. Isostatic Equilibrium Lab
Why does the Earth have high places (the continents) and low places (the ocean basins)?
What controls the elevation of mountains, lowlands, and various regions of the ocean floor?
Adopted from a presentation by Ray Rector

2. Density Calculation
The density of a substance is a measure of how much mass is present in a given unit of volume. 
DENSITY = MASS / VOLUME
                                                                                                                                                    
Example: density of liquid water =
8.33 lb/gal = 64 lb/ft3 = 1.0 gm/cm3
2) We will measure all masses in grams and volumes in cubic centimeters (cm3), so all of our densities will be in grams per cubic centimeter (gm/cm3). 2

3. Density Calculation Measuring mass is easy; we use a gram scale.
We’ll use two methods to measure volume:
Linear dimensions (for objects that are rectilinear):
Volume (cm3) = length (cm) x width (cm) x height (cm)
                                                                                                                                                    
2) Water displacement (for objects that have an irregular shape) 3

4. Density Calculation
An object’s volume will displace an equal volume of water in a graduated cylinder. 4

5. Density Calculation An object’s density is a function of:
Open spaces inside
Chemical composition (atomic weight of the elements that make up the substance)
Atomic weight = the number of protons plus neutrons in an element
Example:
wood is mostly carbon (C): atomic weight = 12
a fishing weight is mostly lead (Pb): atomic weight = 207 5

6. Isostatic Equilibrium Lab
Why does the Earth have high places (the continents) and low places (the ocean basins)?
What controls the elevation of mountains, lowlands, and various regions of the ocean floor?
Answer: parts of the crust vary in thickness & density.
Adopted from a presentation by Ray Rector

7. Earth’s Layered Structure
Core
Mantle
Oceanic crust
Continental crust
Lithosphere: the crust (either oceanic or continental) plus the uppermost part of the mantle; forms a layer of cool, rigid rock that is broken up into moving plates.
Crust

8. Earth’s Layered Structure
The lithosphere is broken up into plates that move horizontally across the Earth.

9. Earth’s Layered Structure
Today’s lab is not about horizontal movements of the Earth’s plates, but rather about vertical movements and vertical elevations of the Earth’s crust.

10. Elevation of Earth’s Crust

11. Two Main Types of Crust
Continental Crust
Oceanic Crust

12. The Concept of Isostasy
Isostasy is the principle of buoyancy applied to the Earth’s crust.
Isostasy: a state of gravitational equilibrium in which an area of crust “floats” in a balanced way on the denser rock of the mantle below.
The elevation of any part of the Earth’s crust is a function of the THICKNESS and DENSITY of the crust.

13. The Concept of Isostasy
These figures show how either thickness differences or density differences determine how high the wood blocks will float.

14. Isostasy and Isostatic Equilibrium
The top of the wood will ride higher if:
The wood block is thicker
The wood block is less dense

15. Isostatic Adjustment – Ice Caps
Isostatic Response to Changing Ice Weight
Glacial Adjustment

16. Isostatic Adjustment - Orogeny