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tokens: the protosolar disk. In addition, D/H ratios can readily be modified by non-nebular processes. For example, the D/H ratio of Rumuruti type and ordinary chondrites is higher than that in comets, which Alexander et al. ( 2012 ) attribute to iron oxidation in their parent bodies. 4.5. Water in Chondrites If carbonaceous and non-carbonaceous chondrites formed on opposite sides of the snowline, where Jupiter formed, why do some carbonaceous chondrites have relatively low water and carbon contents like those in some non-carbonaceous chondrites? CM, CI, and CR chondrites have the highest contents of water and carbon among chondrites, but CO and CV have lower amounts that are comparable to those in some of the least metamorphosed ordinary chondrites (Krot et al. 2014 ). Krot et al. ( 2015 ) infer that CI, CM, and CR chondrites were altered under water/rock mass ratios of up to 0.6, whereas CV and CO chondrites were altered at lower water/rock ratios of 0.1–0.2. We do not know the answer to this issue but note that water contents of carbonaceous chondrites are related to matrix contents and that the coarse-grained matrix material likely contained more water than the fine-grained matrix rims. Thus, the low water content of CO and CV chondrites may reflect their low content of coarse-grained matrix material relative to CI, CM, and CR chondrites (Scott Krot 2014 ). We also note that comets can contain more rock than ice (Brownlee 2014 ; Davidsson et al. 2016 ), much less ice than the predicted theoretical water-rock ratio beyond the snowline of 1.2 (Krot et al. 2014 ; Palme et al. 2014 ). 5. How and When Were the Two Isotopic Populations Mixed Together in the Asteroid Belt? The isotopic dichotomy in the solar system lasted until at least 3–4 Myr after CAI formation, the likely accretion time of CR chondrites, which are the least metamorphosed and altered chondrites and have the highest concentration of presolar grains (Zhao et al. 2013 ; Budde et al. 2017 ; Krot Nagashima 2017 ). The two isotopic populations were then intermixed, most likely by the migration of the giant planets before the gas had dissipated in the disk. In the Grand Tack model, once Jupiter and Saturn reached masses of ∼50 M ⊕ , they migrated inward across the asteroid belt so that it was first emptied and then repopulated with S-type asteroids, which formed in the belt, and C-types, which formed outside Jupiter (Walsh et al. 2011 ). Alternatively, planetesimals from the giant planet region may have been scattered into the asteroid belt as a natural side-effect of the growth of giant planets (Kretke et al. 2017 ; Raymond Izidoro 2017 ). Raymond Izidoro ( 2017 ) show that scattering during the rapid growth of the gaseous envelopes of giant planets would have scattered nearby planetesimals in all directions and may have delivered water to the growing Earth. However, the Grand-Tack model has the advantage that it creates a strongly mass-depleted belt with roughly equal masses of S- and