Convection currents occur within:
Focus Question: What is the source of energy for convection currents
in the geosphere?
Convection currents in the magma drive plate tectonics.
Heat generated from the radioactive decay of elements deep
in the interior of the Earth creates magma (molten rock) in the aesthenosphere.
The aesthenosphere (70 ~ 250 km) is part of
the mantle, the middle sphere of the Earth that extends to 2900
km. It contrasts with the more rigid lithosphere, the outer
shell of the Earth (0 ~ 70 km) that contains the continental
crust (made up of less dense granitic rocks) and the oceanic
crust (more dense basaltic rocks) that are broken up into more
than a dozen rigid plates.
For more info, see:
do the plates move?
Large convection currents in the aesthenosphere transfer
heat to the surface, where plumes of less dense magma break apart the
plates at the spreading centers, creating divergent plate boundaries.
As the plates move away from the spreading centers, they
cool, and the higher density basalt rocks that make up ocean crust get
consumed at the ocean trenches/subduction zones. The crust is recycled
back into the aesthenosphere.
Subduction of Plates
Because ocean plates are denser than continental plates, when these
two types of plates converge, the ocean plates are subducted beneath
the continental plates. Subduction zones and trenches are convergent
margins. The collision of plates is often accompanied by earthquakes
Focus Question: Where is the source of heat in the atmosphere-hydrosphere
The source of heat is from the sun, above.
The teachers were asked to sketch the variation in the distribution
of heat from the equator to the poles, noting the difference in
the angle of incidence with latitude and how this would affect heating.
This led to discussions about the multiple currents/cells that are driven
by unequal heating driving currents both vertically (creating high and
low pressure systems by descending and ascending air masses) and horizontally.
Focus Question: If the hydrosphere were a closed system
with only an external source of heat from the sun, what simple temperature
patterns would you expect to see in the ocean basins?
One would expect to see warmer temperatures at the equator
and cooler temperatures at the poles leading to two large convection cells
from the equator to the poles, one in each hemisphere.
Teachers map their hypotheses:
Focus Question: How well does this simple basin model
illustrate the real convection cells in the ocean-atmosphere system?
The teachers pondered this and other questions to be addressed
further during Session #2 on November 2, 2002.