ΔE 21.4, loose: different enough that you should pick on purpose. Primer Red Oxide is a little darker, much more saturated, cooler than Martian Ironearth.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Primer Red Oxide is a little darker, much more saturated, cooler than Martian Ironearth.
The same difference applies the other way round: Martian Ironearth is a little lighter, much more muted, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Martian Ironearth on the colour wheel See Primer Red Oxide on the colour wheel
All matches: Martian Ironearth equivalents · Primer Red Oxide equivalents