DYNAMIC PLANET INVESTIGATION 3 NOTES

CONVECTION CELLS Definition – a motion in a fluid that is caused by heating from below and cooling from above Definition – a motion in a fluid that is caused by heating from below and cooling from above

Examples Heating of the corn syrup demonstration Heating of the corn syrup demonstration Oatmeal demonstration Oatmeal demonstration Home heating systems Home heating systems Convection oven Convection oven

When a fluid is heated, it expands and lowers its density slightly When a fluid is heated, it expands and lowers its density slightly The expanded fluid (less dense) rises  The expanded fluid (less dense) rises  Reaches cooler surroundings  shrinks, becoming more dense  sinks  heated again… Forms CONVECTION CELLS

Convection of the Earth’s Mantle The mantle convects in the form of gigantic convection cells The mantle convects in the form of gigantic convection cells

Many materials act like solids on short time scales but like liquids on much longer time scales Many materials act like solids on short time scales but like liquids on much longer time scales

Examples Silly Putty Silly Putty Glass Glass Wax Wax

These materials flow and take on a new shape, even though it seems like a solid These materials flow and take on a new shape, even though it seems like a solid The Earth’s mantle behaves in the same way The Earth’s mantle behaves in the same way The speeds of flow in the mantle are only a few centimeters per year OR as fast as your fingernail grows The speeds of flow in the mantle are only a few centimeters per year OR as fast as your fingernail grows

The Lithosphere and Asthenosphere

The Lithosphere Outermost part of the Earth Outermost part of the Earth Cooler Cooler Remains rigid Remains rigid Does not convect Does not convect Made up of the crust & uppermost part of the mantle Made up of the crust & uppermost part of the mantle Consists of several pieces called lithospheric plates Consists of several pieces called lithospheric plates

The Asthenosphere Below the lithosphere Below the lithosphere Zone where mantle rocks are just hot enough & under enough pressure to deform & change shape Zone where mantle rocks are just hot enough & under enough pressure to deform & change shape Able to convect  moving the lithosphere Able to convect  moving the lithosphere

Mid-Ocean Ridges All the Earth’s oceans have a continuous mountain range, called a mid-ocean ridge All the Earth’s oceans have a continuous mountain range, called a mid-ocean ridge Located above rising currents in the mantle convection cells Located above rising currents in the mantle convection cells Stand high because they are heated by hot rising material which expands the rocks Stand high because they are heated by hot rising material which expands the rocks

As hot mantle rock rises, some melts forming magma As hot mantle rock rises, some melts forming magma Magma is less dense than surrounding rock, rises to form volcanoes along the ridge Magma is less dense than surrounding rock, rises to form volcanoes along the ridge As rock rises, temperature stays the same but pressure decreases (less weight of rock above) As rock rises, temperature stays the same but pressure decreases (less weight of rock above)

Melting temperature decreases as pressure decreases, why some rising rock forms magma Melting temperature decreases as pressure decreases, why some rising rock forms magma Magma reaches surface, solidifies to form basalt Magma reaches surface, solidifies to form basalt

New crust is formed, moves away from the crest of the ridge Due to movement of the mantle Due to movement of the mantle Due to downhill slope of the ridge away from the crest Due to downhill slope of the ridge away from the crest

Movement of new oceanic crust in both directions  sea floor spreading Movement of new oceanic crust in both directions  sea floor spreading