Presentation on theme: "Isostatic Equilibrium Lab Why does the Earth have high places (the continents) and low places (the ocean basins)? What controls the elevation of mountains,"— Presentation transcript:
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 1)The density of a substance is a measure of how much mass is present in a given unit of volume. DENSITY = MASS / VOLUME 2) We will measure all masses in grams and volumes in cubic centimeters (cm 3 ), so all of our densities will be in grams per cubic centimeter (gm/cm 3 ). Example: density of liquid water = 8.33 lb/gal = 64 lb/ft 3 = 1.0 gm/cm 3
3 Density Calculation Measuring mass is easy; we use a gram scale. We’ll use two methods to measure volume: 1)Linear dimensions (for objects that are rectilinear): Volume (cm 3 ) = length (cm) x width (cm) x height (cm) 2) Water displacement (for objects that have an irregular shape)
4 An object’s volume will displace an equal volume of water in a graduated cylinder. Density Calculation
5 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 Density Calculation
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 Crust Crust 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.
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.
Two Main Types of Crust Oceanic Crust Continental Crust
The Concept of Isostasy 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. Isostasy is the principle of buoyancy applied to the Earth’s 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