Earth Science 3. Plate tectonics operating over geologic time has changed the patterns of land, sea, and mountains on Earth’s surface. As the basis for understanding this concept: a. Students know features of the ocean floor (magnetic patterns, age, and sea-floor topography) provide evidence of plate tectonics. b. Students know the principal structures that form at the three different kinds of plate boundaries. c. Students know how to explain the properties of rocks based on the physical and chemical conditions in which they formed, including plate tectonic processes. d. Students know why and how earthquakes occur and the scales used to measure their intensity and magnitude. e. Students know there are two kinds of volcanoes: one kind with violent eruptions producing steep slopes and the other kind with voluminous lava flows producing gentle slopes.

Inside the Earth

Plate Boundaries Tectonic Plates move around on the Earth’s mantle. When plates come into contact with each other, we get… Divergent Boundaries Two plates move away from one another (diverge) Convergent Boundaries Two plates move toward each other (converge) Transform Boundaries Plates slide past one another

Convergent Boundaries Continental-oceanic convergence A boundary where two plates move toward one another Subduction – the movement of one plate downward into the mantle beneath the edge of the other plate. Downgoing plate is always oceanic lithosphere Plate at the surface is either oceanic or continental

Theory of Sea-Floor Spreading Lava cools to form basalt – an iron-rich volcanic rock that makes up the ocean floor. Scientists noticed magnetic patterns in the basalt on either side of a mid-ocean ridge. A mid-ocean ridge is general term for an underwater mountain system consisting of various mountain ranges, typically having a valley known as a rift running along its spine, formed by plate tectonics.

Scientists developed the theory of sea-floor spreading to explain the patterns. They explained that lava was pushed up between the two plates and formed new ocean crust at the ridge, pushing the old crust away Mid-ocean ridges are geologically active, with new magma constantly emerging onto the ocean floor and into the crust

Convection Currents Thermal Convection (in the mantle) – Material is heated at the core/mantle boundary Rises upward, spreads out horizontally Cools Sinks back into the interior These convection currents provide the driving force that moves the tectonic plates

Anatomy of an Earthquake Focus- location of first motion of earthquake Epicenter- spot on Earth’s surface directly above focus Fault- fracture in body of rock along which rock masses move Fault scarp- cliff formed by a fault that reaches the Earth’s surface

Inside a Volcano.

3 Volcano Types: Shield Volcano Cinder Cone Composite Cones

Shield Volcanoes Fluid, fast, basaltic lava Warrior’s shield Broad, slightly domed Most have grown from the ocean-floor to form islands (Hawaii and Iceland)

Cinder Cones Lava fragments that harden in the air. Loose pyroclastic material comes to rest. Steep-sided slope (salt mound) Generally small Magma in the pipe solidifies after the eruption. Volcano doesn’t erupt again.

Composite Cones “Stratovolcano” Lahar Large, symmetrical (ice-cream cone) Layers of lava & pyroclastic material Lahar destructive mudflow