Chondrules and chondrite classes as impact pyroclastics

If chondrules formed by impact into a regolith, and chondrules behaved as open systems during their formation, then the diversity of chondrule compositions presumably reflects the diversity in the intensity of impact. It is then a small step to assume that the redox state of the resultant chondrite similarly depends on the violence of impacts locally. The remaining factor in forming chondrites concerns the matter of assembling the components, and producing small variations in the amount of matrix and metal in relation to the chondrules. The size and distribution of the chondrules and metal, which are characteristic of many classes of chondrites, suggests sorting before or during accumulation. Again, a great many mechanisms have been proposed for how this might have been achieved in the nebula, but I think it unlikely that this process occurred in the nebula because the meteorites managed to preserve compositions so close to cosmic and because aerodynamic sorting alone fails quantitatively. Density sorting is also required and this in turn needs the presence of at least a weak gravity field. Some meteorite parent bodies must have experienced degassing in their early stage to turn CI compositions into ordinary chondrite compositions and may have had thick dusty surfaces that were easily mobilized by gases evolving from the interior. Density and size sorting may have occurred in the surface layers as the upward drag forces of gases (mainly water) acted against the downward force of gravity.