Isostatic Equilibrium Lab

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# Isostatic Equilibrium Lab - PowerPoint PPT Presentation

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. Density Calculation.

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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

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

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

Density Calculation

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

4

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

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

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

Earth’s Layered Structure

The lithosphere is broken up into plates that move horizontally across the Earth.

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.

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.
The Concept of Isostasy

These figures show how either thickness differences or density differences determine how high the wood blocks will float.

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