LAUSR

Geophysics The boundaries between rocks with different physical properties in Earth's interior come from either a change in crystal structure or a change in chemical composition. Wu et al. examined the roughness of the boundary between Earth's upper and lower mantle, thought to form from a change in mineral structure (see the Perspective by Houser). To their surprise, in some locations, the boundary has small-scale roughness that requires some chemical difference above and below the boundary. This observation provides evidence of partially blocked mantle circulation that leads to some chemical differences between the upper and lower mantle. Science , this issue p. [736][1]; see also p. [696][2] [1]: /lookup/doi/10.1126/science.aav0822 [2]: /lookup/doi/10.1126/science.aaw4601