Download Convection in the Mantle: Using a Lava Lamp as a

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Convection in the Mantle: Using a Lava Lamp as a Model
A. Background: Density and Earth’s Lithospheric Plates
You already know that substances that are more dense tend to sink while substances that are less
dense tend to float. In addition, you’ve learned that heated substances tend to be less dense than
cooled substances. In the case of Earth’s lithospheric plates, this means that oceanic plates, which
are colder and denser than continental plates, will subduct (sink underneath) the continental plates
at a convergent boundary. Older, colder, denser oceanic plates will also subduct (sink underneath)
the relatively younger, warmer, less dense oceanic plates at a convergent boundary.
B. Lava Lamp Observation (Convection Current)
You previously learned that convection currents are the circulation (movement) of heat within a fluid
due to the different densities of the hotter and cooler parts. This circulation due to changes in the
temperature and density of a substance can be demonstrated by a lava lamp. Observe what
happens as the "lava" inside the lamp is heated. Then, answer the following questions:
1. What is the heat source in the lava lamp?
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2. Describe what happens to the “lava” at the bottom of the lamp (changes in shape, density, and
movement) when the lamp is “on”. What is the cause of these changes?
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3. Describe what happens to the “lava” after it reaches the top of the lamp (changes in shape,
density, and movement). What is the cause of these changes?
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4. Draw and label the convection current in the lava lamp. Identify the hottest and coolest parts of
the lamp, as well as the most and least dense “lava”, and use arrows to show direction of
movement.
C. Reflections upon Convection in the Earth’s Mantle
Deep in the Earth’s core, it is extremely hot due to chemical reactions as well as intense pressure
from the rest of the earth. This heat affects the Earth’s mantle and sets up a convection current,
particularly in the softer, taffy-like asthenosphere of the upper mantle that carries the earth’s
lithospheric plates.
5. What makes the earth’s core so hot (give two reasons)?
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6. Think about the three types of heat transfer – radiation, conduction, convection; how does heat
move from Earth’s core to the mantle?
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7. What do you think happens to the rock in Earth’s mantle when it gets hot?
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8. Draw and label the diagram of the Earth’s interior using the key vocabulary below:
oceanic crust
convection current
convergent boundary
continental crust
hotter
mid-ocean ridge
lithosphere
colder
ocean trench
asthenosphere
divergent boundary
volcanic mountains