The formation mechanism of terrestrial planetary cores is still poorly unde
rstood, and has been the subject of numerous experimental studies(1-3). Sev
eral mechanisms have been proposed by which metal-mainly iron with some nic
kel-could have been extracted from a silicate mantle to form the core. Most
recent models involve gravitational sinking of molten metal or metal sulph
ide through a partially or fully molten mantle(4,5) that is often referred
to as a 'magma ocean'. Alternative models invoke percolation of molten meta
l along an interconnected network (that is, porous flow) through a solid si
licate matrix(6,7). But experimental studies performed at high pressures(1-
3) have shown that, under hydrostatic conditions, these melts do not form a
n interconnected network, leading to the widespread assumption that formati
on of metallic cores requires a magma ocean. In contrast, here we present e
xperiments which demonstrate that shear deformation to large strains can in
terconnect a significant fraction of initially isolated pockets of metal an
d metal sulphide melts in a solid matrix of polycrystalline olivine. Theref
ore, in a dynamic (nonhydrostatic) environment, percolation remains a viabl
e mechanism for the segregation and migration of core-forming melts in a so
lid silicate mantle.