Dr Thomas developed a model with colleagues at University of California Los Angeles (UCLA), which uses a recently discovered phase change (when atoms are compressed into crystals under high pressure) in the lowest part of the Earth’s mantle. They propose that temperature changes in this area can result in the creation of two seismic layers near the core-mantle boundary, the second of which has been recently discovered by Dr Thomas.
The two seismic layers can provide a sensitive thermometer with which researchers can take the temperature of the Earth’s lowermost mantle. The layers also enable scientists to examine whether cold subducted lithosphere (cold areas beneath a plate which can cause earthquakes) is reaching the core-mantle boundary, and whether hot material rises from the area between the core and mantle.
In the first case, the two seismic layers should be visible in seismic waves that travel through the Earth; the latter case would not show any layers. This would be a strong case for the convection of the whole mantle that is still a highly debated issue in the Earth Sciences.
From a UL press release.