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Here we discuss the current state of knowledge on how atmospheric escapeprocesses can fractionate noble gas isotopes and moderately volatilerock-forming elements that populate primordial atmospheres, magma ocean relatedenvironments, and catastrophically outgassed steam atmospheres. Variations ofisotopes and volatile elements in different planetary reservoirs keepinformation about atmospheric escape, composition and even the source ofaccreting material. We summarize our knowledge on atmospheric isotope ratiosand discuss the latest evidence that proto-Venus and Earth captured smallH$_2$-dominated primordial atmospheres that were lost by EUV-drivenhydrodynamic escape after the disk dispersed. All relevant thermal andnon-thermal atmospheric escape processes that can fractionate various isotopesand volatile elements are discussed. Erosion of early atmospheres, crust andmantle by large planetary impactors are also addressed. Further, we discuss howmoderately volatile elements such as the radioactive heat producing element$^{40}$K and other rock-forming elements such as Mg can also be outgassed andlost from magma oceans that originate on large planetary embryos and accretingplanets. Outgassed elements escape from planetary embryos with masses that are$\geq$\,M$_{\rm Moon}$ directly, or due to hydrodynamic drag of escaping Hatoms originating from primordial- or steam atmospheres at more massiveembryos. We discuss how these processes affect the final elemental compositionand ratios such as K/U, Fe/Mg of early planets and their building blocks.Finally, we review modeling efforts that constrain the early evolution ofVenus, Earth and Mars by reproducing their measured present day atmospheric$^{36}$Ar/$^{38}$Ar, $^{20}$Ne/$^{22}$Ne noble gas isotope ratios and the roleof isotopes on the loss of water and its connection to the redox state on earlyMars.

Loss and fractionation of noble gas isotopes and moderately volatile elements from planetary embryos and early Venus, Earth and Mars