Lab 1: Observing and Measuring Earth Materials and Processes

 

Objectives:

  1. To be able to convert between different systems of measurement
  2. To calculate the density and mass
  3. To understand and define isostasy, buoyant and gravitational forces
  4. Understand how gravity v. buoyant force is related to the relative positions of continental v. oceanic crust

 

Introduction:

            What is our goal with this lab?

                        - characterize and classify Earth materials

                        - identify relationships of cause (process) and effect (product)

                        - form hypotheses (ideas to be tested)

                        - devise experiments (tests of materials and hypotheses)

                        - design models (physical, conceptual, mathematical, graphical, or artistic

      representations of something to test or demonstrate how it works)

                        - make inferences (ideas justified with reasonable thinking and evidence)

 

Skip 1A

 

1B: Measuring Earth Materials and Relationships

 

            - All objects have a mass that can be weighed, and a volume it occupies

            - Mass is can be calculated by using a scale, weight under the pull of Earth’s gravity

            - Volume found from linear measurements, or measuring the volume of water it displaces

           

            Metric System – Meters, Liters and Degrees Celsius

 

Linear measurements – exact measurements of length (how long something is)

                                               – measure as exactly as possible, to closest ruler marker

           

Conversions – change from one unit of measure to another

            Example: meters to cm ŕ 1 m x (100 cm / 1 m) = 100 cm

            Example: feet to meters ŕ 3 ft x (0.3048 m / 1 ft) = 0.9144 m

 

Area and Volume

            Area: two-dimensional space (surface of a table)

            Volume: three-dimensional space

                        Box shape – linear volume, length x width x height

                                    Example: 10 cm x 8 cm x 4 cm = 320 cm3

                        Liquid or odd shapes – measure the volume of liquid or the volume of

liquid an object displaces

graduated cylinder: in mL, but 1 mL = 1 cm3

                                                measure from bottom of meniscus, curvature of water

                                                Object: Total volume – Initial volume = Object volume

            Mass

                        Measure with a gram balance

 

            Density (r)

                        The relationship between a material's mass and its volume

                        Mass per unit volume

                        Typically r = g/ cm3

 

1C: Density, Gravity, and Isostasy

 

            Buoyant force (buoyancy) – fluid pressure in response to gravity

                        Object will sink when denser than surrounding fluid

                        Object will rise when less dense than surrounding fluid

                        Floating is a balance between sinking and rising, balance of gravity and buoyancy

                       

            Isostasy (Greek for equal standing):

                        Edward Suess – sea level change from change in volume of ocean water

                        Clarence Dutton – shoreline change from varying level of land

                                                   – Earth’s crust composed of buoyant rocks

                        The equilibrium (balance) condition between floating object and denser fluid

                        Isostasy when the buoyant force = gravitational force

                        Equilibrium line ~ water line

 

1D: Isostasy and Earth’s Global Topography

 

            Histogram (bar diagram)

            Bimodal (shows two levels that are common) – Figure 1.17 B, pp 26

            Hypsographic curve – shows cumulative percentage of the Earth’s spherical surface

                        Important – not the profile of a continent, it represents the whole Earth’s surface

 

            Global Isostasy

                        Continents – 0.84 km above SL

                        Ocean Basins – 3.87 km below SL                  

                        Why? Difference between densities of granite, basalt and the mantle’s peridotite

                        Continents – Granite, Oceans – Basalt, Mantle – Peridotite

 

                        Lab: measure density (mass per unit volume) of granite and basalt samples,

compare to given value for peridotite