On the degassing state and the chemical structure of the Earth's interior inferred from noble gas isotopes-Past and recent views

The degassing state of the Earth's interior is one of the main issues in relation to the evolution of the Earth and has been discussed by many investigators over several decades. I outline some trials to reveal the state of degassing based on noble gas isotopes. Then, based oil noble gas isotope signatures so far obtained, I discuss models of the chemical structure of the Earth's interior which are inevitably related to the degassing state of the Earth. I propose a preferred model which suggests the possibility for the occurrence of relatively undegassed and possibly less fractionated reservoir(s) in the Earth's deep interior, which might be located in a relatively non-convective mantle.