Know That Density Is Measured As Mass Over (Divided By) Volume

Review sheet – Chapter 3

· Understand that the Earth is density-stratified; that each deeper layer contains elements that are more dense (heavier) than the layers above (lightest, least dense elements on surface)

· Know that density is measured as mass over (divided by) volume

· Know that the core contains materials with the greatest density, while the crust contains the least dense materials (elements)

· Know that the Earth is layered (contains a series of concentric layers)

· Understand that the compositional (based on chemical properties) layers of the Earth are the crust (thin, outermost), mantle (thick, middle layer), and core (densest, innermost layer)

· Understand that the Earth is further classified into layers based on physical differences; these layers are the lithosphere (cool and rigid, uppermost; include all of the crust and the upper, rigid portion of the mantle), asthenosphere (hot, partially melted portion of the upper mantle), lower mantle (portion of the mantle that extends to the core, rigid) and core (includes the inner and outer core; the inner core is solid, while the outer core is viscous)

· Understand that both oceanic and land crust is found in the lithosphere

· Understand that the lithosphere floats on the asthenosphere

· Understand that the source of the Earth’s heat is radioactive decay (then and now)

· Know the difference between oceanic and land crust: oceanic crust is thin and made up of heavy/dense basalt, while continental crust is thick and made up of (relatively) light granite

· Understand that the less dense continental crust does not sink as deep into the asthenosphere and so rises high above the oceanic crust, which is heavier and sinks much deeper into the asthenosphere

· Know that buoyancy is the ability of objects to float in a fluid by displacing a volume of fluid equal in weight to the floating object’s own weight

· Understand that lithospheric plates float in the asthenosphere because of buoyancy

· Know the evidence for continental drift: parallelism of the shorelines (South America and Africa), discovery of coal (tropical plants) in Antarctica, similarities in fossils across (now) separate continents, “ring of fire” in Pacific Ocean

· Know that Alfred Wegener proposed the theory of continental drift

· Know that Pangaea was the supercontinent which consisted of all the world’s continents before they separated (into the continents we see today)

· Know that the age of oceanic crust is no less than 200 million years old

· Know that the age of continental crust is ~4 billion years old (much, much older than oceanic crust)

· Understand that scientists use radioactive (radiometric) dating to age the continental and oceanic crusts

· Understand the process of seafloor spreading; that new ocean floor is generated at mid-ocean ridges and spreads outward; understand that this pushes (spreads apart) continents on either end of this ridge as a result

· Know that seafloor spreading is powered by convection currents; know that convection currents refer to slow-flowing circuits of material in the asthenosphere

· Understand the theory of plate tectonics; the heat-driven large-scale movements of the Earth’s lithosphere over the asthenosphere; a key principle of plate tectonics is that the lithosphere exists as separate and distinct tectonic plates (~13) which ride on the fluid/plastic asthenosphore

· Know that newly-formed oceanic crust is hot, and so less dense; therefore it sits higher on the asthenosphere, whereas older oceanic crust is cool, and so denser; therefore it sits lower on the asthenosphere. As you move away from the spreading center (mid-ocean ridge), the ocean contour shrinks in volume, with the warmest (newest) regions existing as tall ridges rising from the ocean floor

· Know that oceanic crust ages as it spreads outward from the spreading center (towards the continents); the oldest oceanic crust would therefore be closer to the continents, and the newest would be at or near the spreading center (mid-ocean ridge)

· Know that the rate of seafloor spreading is ~2-12cm per year

· Understand that the constant creation of new, oceanic crust must be balanced by the destruction of crust elsewhere

· Understand the process of subduction; whereby crust plunges back down into the mantle (regions of crust destruction are called subduction zones)

· Understand that because oceanic crust is denser, when it meets continental crust, it subducts beneath the continental plate

· Understand that lithospheric plates interact with one another; diverging (coming apart); converging (coming together) or sliding past one another

· Know that divergent plate boundaries are regions of crustal formation; mid-ocean ridges

· Know that the Mid-Atlantic Ridge is the Atlantic Ocean’s mid-ocean ridge system (the East Pacific Rise occurs in the Pacific)

· Understand that divergent plate boundaries originate beneath continental crust and begin as a rift valley, which slowly develops into an ocean basin

· Know that the Red Sea is a ‘juvenile’ ocean

· Understand that plates may converge in one of three ways: continental to continental; continental to oceanic; oceanic to oceanic

· Understand that the denser plate will always subduct beneath the less dense plate during convergence; therefore an oceanic plate will always subduct beneath a continental plate, and the older (denser) oceanic plate will subduct beneath the newer (less dense) oceanic plate

· Know that volcanoes frequently form when an oceanic plate converges with a continental plate, or when 2 oceanic plates converge

· Know that the Marianas Trench is the world’s deepest oceanic trench (the deepest part of the world’s ocean), and was formed by the convergence of 2 oceanic plates (1 subducting beneath the other)

· Know that the Marianas Trench is ~11,000 meters (36,000 feet)

· Understand that when 2 continental plates converge, neither is subducted (same age; same density) so they are instead pressed and folded into each other, creating mountain ranges

· Know that the Himalayas (the highest of the world’s mountain ranges) are an example of 2 continental plates converging (the Indian plate and the Asian plate)

· Understand that hot spots are further evidence of plate tectonics; hot spots are not located at a plate boundary, but instead are a single source of rising magma. Volcanic island chains form as a result of the plate moving over the stationary hot spot. Know that the Hawaiian Islands are an example of a plate moving slowly over a stationary hot spot (the Hawaiian Islands are NOT the result of convergence or divergence)

· Understand that transform boundaries are regions where 2 plates slide past one another

· Understand that transform boundaries are offset horizontally from a vertical spreading center (the result of spreading occur on a spherical Earth)

· Know that mid-oceanic ridges are marked by numerous transform faults, and that California’s San Andreas fault is an example of a transform fault

· Understand that earthquakes may result when 2 plates slide past each other in opposite directions

· Know that oceans cannot grow indefinitely – eventually they will collide with land on the other side of the planet

· Know that the Wilson Cycle is the collective stages of ocean basin formation and destruction, consisting of an embryonic (rift valley), juvenile (Red Sea), mature (Atlantic Ocean), declining (Pacific Ocean), terminal (Mediterranean Sea), and suturing (Himalayas) stage

· Be comfortable with examples of each of the stages in the Wilson Cycle (as summarized above)