From Tim Sprod
Lawrence D’Oliveiro wonders whether continental crust is disappearing (17 November 2007, p 24). In fact, new continental crustal material is continually created by partial melting of rocks in the denser and silica-poor mantle and partial solidification of existing magmas. Both processes produce magmas richer in silica – the building blocks of continents. These rise and solidify, forming new crustal material. When teaching this to students, I likened it to the formation of scum when you boil fruit to make jam. The continents, I would tell them, are truly the scum of the Earth.
Taroona, Tasmania, Australia
