THANKS to a load of balls, we鈥檙e a little closer to understanding how the continents, mountains and oceans came to be.
The mantle flows in convection 鈥渃ells鈥� as it warms and rises, then cools and sinks. Rocky plates riding on top are smashed together and pulled apart to form mountains and oceans. Over geological timescales, the cells鈥� flow changes direction, but why they do so is a mystery. One 40-year-old theory is that when thick continental crust blankets the cell beneath it, heat is trapped. This creates rising currents that alter flow direction.
Now Jun Zhang and colleagues at New York University have built a simulation showing part of the process in action. They filled a container with fluid, and heated it from below to create convection. Next they added nylon spheres, which sank to the base. The balls bunched, blanketing part of the heat plate and creating a contrast in heat flux that flipped the flow. Though the set-up does not mimic how continents sit above the mantle, it shows how shifting masses can alter convection (Physical Review Letters, ).
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The experiment 鈥渕akes substantial progress鈥� on the old theory, says John Whitehead of the Woods Hole Oceanographic Institution in Massachusetts.
