Final answer:
The asthenosphere is the layer with the most active convection currents due to its partially molten upper mantle that allows for fluid movements.
Explanation:
The asthenosphere is the mechanical layer of Earth that has the most active convection currents. It is a partially molten upper mantle layer that behaves plastically and allows for fluid movements, contributing to the motion of the lithospheric plates. Seismic waves passing through the asthenosphere indicate its solid nature at shorter time scales.
Learn more about Earth's layers here:
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