Yes the earth mantle convects into two layers,but there is a third layer mentioned.
1.The upper mantle
2.The lower mantle
3.D" layer(Core–mantle boundary)

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The mantle is divided into sections based upon results from seismology. These layers (and their depths) are the following: the upper mantle (base of the crust–410 km)3, the transition zone (410–660 km), the lower mantle (660–2891 km), and in the bottom of the latter region there is the anomalous D" layer with a variable thickness (on average ~200 km thick)2456.
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information quoted from http://en.wikipedia.org/wiki/Earth_mantle

http://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Earth-crust-cutaway-english.svg/350px-Earth-crust-cutaway-english.svg.png

How does the mantle of the earth move?
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Due to the temperature difference between the Earth's surface and outer core, and the ability of the crystalline rocks at high pressure and temperature to undergo slow, creeping, viscous-like deformation over millions of years, there is a convective material circulation in the mantle4. Hot material upwells, while cooler (and heavier) material sinks downward. Downward motion of material often occurs at convergent plate boundaries called subduction zones4, while upwelling of material can take the form of plumes. Locations on the surface that lie over plumes will often increase in elevation (due to the buoyancy of the hotter, less-dense plume beneath) and exhibit hot spot volcanism.
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information quoted from http://en.wikipedia.org/wiki/Earth_mantle
Please read the full article of the page go to Contents and then click on 4 Movement it will explain how the mantles move
Source(s):
http://en.wikipedia.org/wiki/Earth_mantle

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