If this had been the case, then a Moon formed from earth's mantle, impactor's mantle, or a mixture would all show a depletion of siderophiles.
(this; had been; the case) (a Moon; formed; from earth's mantle, impactor's mantle, or a mixture; T:then)
this a Moon
had been formed
the case
from earth's mantle, impactor's mantle, or a mixture T:then