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