  Isotopic anomalies provide a means of probing the materials responsible for
the formation of terrestrial planets. By analyzing new iron isotopic anomaly
data from Martian meteorites and drawing insights from published data for O,
Ca, Ti, Cr, Fe, Ni, Sr, Zr, Mo, Ru, and Si, we scrutinize potential changes in
the isotopic composition of the material accreted by Mars and Earth during
their formation.
  A Principal Component Analysis of isotopic anomalies in meteorites identifies
three main clusters (forming the three parts of the isotopic trichotomy): CI,
CC=CM+CO+CV+CR, and NC=EH+EL+H+L+LL.
  Our results suggest that Earth is primarily an isotopic mixture of ~92% E, 6
% CI, and <2% COCV and O. Mars, on the other hand, appears to be a mixture of
~65% E, 33% O, and <2% CI and COCV. We establish that Earth's CI contribution
substantially increased during the latter half of its accretion. Mars began
accreting a mix of O and E but predominantly accreted E later.
  Mars' changing isotopic makeup during accretion can be explained if it
underwent gas-driven type I migration from its origin near the O - E boundary
to a location well within the E region during the first few million years of
solar system history. Earth's later increased CI contribution may be attributed
to the stochastic impact of an interloper carbonaceous embryo that moved inside
the inner solar system region while nebular gas was still present, and
subsequently participated in the stage of chaotic growth.
  The recent findings of Si isotopic anomalies in enstatite chondrites when
compared to terrestrial rocks likely stems from insufficient correction for
high-temperature equilibrium isotopic fractionation. With appropriate
adjustments for this influence, both the silicate Earth and enstatite
chondrites exhibit comparable Si isotopic anomalies, reaffirming a genetic link
between them.
