  The Earth is known to be depleted in volatile lithophile elements in a
fashion that defies easy explanation. We resolve this anomaly with a model that
combines the porosity of collisionally grown dust grains in protoplanetary
disks with heating from FU Orionis events that dramatically raise
protoplanetary disk temperatures. The heating from an FU Orionis event alters
the aerodynamical properties of the dust while evaporating the volatiles. This
causes the dust to settle, abandoning those volatiles. The success of this
model in explaining the elemental composition of the Earth is a strong argument
in favor of highly porous collisionally grown dust grains in protoplanetary
disks outside our Solar System. Further, it demonstrates how thermal (or
condensation based) alterations of dust porosity, and hence aerodynamics, can
be a strong factor in planet formation, leading to the onset of rapid
gravitational instabilities in the dust disk and the subsequent collapse that
forms planetesimals.
