Convection in the Mantle

Keyterms Density Density-mass/volume. The amount of matter in a given area or volume of that matter. Fluid Fluid-matter that can flow. Can be solids, liquids, or gasses Convection Convection-heat transfer within a fluid. Convection current Convection current -a current that develops from a fluid moving from an area of high density to an area of low density.

How do convection currents form? Convection currents occur when fluids heat unevenly and areas develop that are different in density

What are examples of convection currents?

Lava Lamps (see demo)

Boiling water

Ocean Currents

Air currents in clouds

The Mantle

What is the theory of plate tectonics? The theory of plate tectonics explains the formation and movement of Earth’s plates. The lithosphere is broken into sections called plates.

Plate Boundaries: Divergent Boundaries- The place where two plates (pieces of the lithosphere) move apart. Most divergent boundaries occur along a mid- ocean ridge where sea-floor spreading occurs.

What is a mid-ocean ridge? It is an undersea mountain chain where new ocean floor is produced at a divergent boundary.

Convergent Boundaries: The place where two plates come together (often called a collision). When two plates collide, the density of the plate determines which one comes out on top.

Convergent Boundaries: 2 continental plates collide= formation of mountains 1 oceanic + 1 continental collide= oceanic sinks beneath the continental plate (subduction) and forms a trench (a narrow, deep valley along the ocean floor). Subduction- the process by which oceanic crust sinks beneath a less dense plate.

Subduction Diagram

Transform Boundaries: A place where two plates slip past each other, moving in opposite directions. Earthquakes often occur along transform boundaries, but crust is neither created nor destroyed.

Diagram of plate movement:

Evidence for Plate Tectonics Pangaea- The name of the single landmasss that broke apart 200 million years ago and gave shape to today’s continents.

Evidence for a Supercontinent Land features: mountain ranges and coal fields appear to line up according to the shape of continents. Fossils: from ancient animals appear to link continents together as well- mesosaurus, lystrosaurus (freshwater reptiles), glossopteris (plant). Climate: temperature changes at specific locations show that continents may have shifted toward or away from the equator over time.

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Evidence for Plate Tectonics Sea-Floor Spreading- the process by which molten material adds new oceanic crust to the ocean floor. The sea floor spreads apart along both sides of a mid-ocean ridge (divergent boundary), as new crust is added.

Sea-Floor Spreading Diagram

How do we know the sea-floor actually spreads? Evidence from molten material- new material is erupting along mid-ocean ridges. Evidence from drilling samples- the age of rocks have been identified through drilling samples. Rocks farther from the ridge were the oldest, the youngest rocks were always in the center of the ridges.

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