The existing range of compositional estimates of the Earth reflects our lack of understanding of what were the processes and building blocks ( chondritic meteorites ) that contributed to its formation.
22.
Planetary scientists classify chondritic IDPs in terms of their diminishing degree of oxidation so that they fall into three major groups : the carbonaneous, the ordinary, and the enstatite chondrites.
23.
Hafnium / tungsten ( Hf / W ) isotopic ratios, when compared with a chondritic reference frame, show a marked enrichment in the silicate earth indicating depletion in Earth's core.
24.
Like many chondrites, Allende is a breccia, and contains many dark-colored clasts or " dark inclusions " which have a chondritic structure that is distinct from the rest of the meteorite.
25.
For some of the less-studied stony meteorite falls, it is not known whether the object is chondritic; thus the number of meteorites that can be so grouped is 4 % lower than shown above.
26.
The mantle is assumed to have undergone chondritic evolution, and thus deviations in initial 143 Nd / 144 Nd ratios can provide information as to when a particular rock or reservoir was separated from the mantle within the Earth's past.
27.
The evidence for the Alvarez impact theory is supported by chondritic meteorites and asteroids which have an iridium concentration of ~ 455 parts per billion, much higher than ~ 0.3 parts per billion typical of the Earth's crust.
28.
In addition DCO research on primitive chondritic meteorites indicates that Earth is relatively depleted in highly volatile elements compared to chondrites, though DCO's research is further examining whether large reservoirs of carbon may be hidden in the mantle and core.
29.
The high pH is interpreted to be a consequence of serpentinization of chondritic rock that leads to the generation of H 2, a geochemical source of energy that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in Enceladus's plumes.
30.
The "'CHondritic Uniform Reservoir "'or "'CHUR "'is a scientific model in astrophysics and geochemistry for the mean chemical composition of the part of the Solar Nebula from which, during the formation of the Solar System, chondrites formed.
