Investigation: Isostasy and Global Elevation Patterns Student Learning Outcome : Quantify relationships between mass, volume, and density Calculate the density of basalt and granite samples from measurements of their mass and volume Calculate the mean and standard deviation of density for granite and basalt sample populations Generalize basalt and granite samples as representative of typical oceanic and continental crust Visualize Archimedes’ principle that a floating object displaces a volume of liquid equal to the object’s mass Explain the bimodal distribution of global elevations as result of isostatic equilibrium among oceanic and continental crust

Archimedes’ Principle: “A floating body will displace a volume of fluid whose mass is equal to that of the body” Increase body density, body floats lower in fluid Increase fluid density, body floats higher in fluid

Increase in body height, body floats higher in fluid . . . Archimedes’ Principle: “A floating body will displace a volume of fluid whose mass is equal to that of the body” Increase in body height, body floats higher in fluid . . . but same percentage of icebergs’ heights (~10%) are above the water surface

Archimedes’ Principle: “A floating body will displace a volume of fluid whose mass is equal to that of the body” Link to wooden block floating in water model . . .

Archimedes’ Principle: “A floating body will displace a volume of fluid whose mass is equal to that of the body” Link to wooden block floating in water model . . . Think of oceanic crust as a thinner denser block “floating” lower on underlying asthenosphere than continental crust Oceanic Crust Column Continental Crust Column

Concept of Hypsographic Curve What variables are being presented? How are variables related?

Concept of Hypsographic Curve What variables are being presented? How are variables related? General Patterns? Responsible Processes?

Part A. Comparing Densities of Oceanic and Continental Crust

Part A. Comparing Densities of Oceanic and Continental Crust

Part B. Testing the Isostasy Prediction Let’s calculated the hydrostatic pressure at the base of the asthenosphere for the “Average Oceanic Crust” column: Assume column sides are 1 m by 1 m! Pressure = density*thickness*gravity First calculate pressure from seawater, then oceanic crust, then mantle. Sum the three pressures for the total pressure

Go to Web-Based Isostasy Model Part C. Predicting Elevations at the “Tops” of Blocks of Continental and Oceanic Crust Go to Web-Based Isostasy Model

Go to Web-Based Isostasy Model Part C. Predicting Elevations at the “Tops” of Blocks of Continental and Oceanic Crust Go to Web-Based Isostasy Model

Part D. Connecting Global Elevation Patterns to Differences in Oceanic and Continental Crust Mostly Continental or Oceanic? Mostly Continental or Oceanic?

Part E. Out of this World: Using isostatic principles to make Predictions for Mars