Comments on: Rosetta Pours Cold Water on Cometary Origins of Earth’s Oceans . . . https://www.habitablezone.com/2014/12/12/rosetta-pours-cold-water-on-cometary-origins-of-earths-oceans/ Tue, 12 May 2026 20:11:45 -0700 hourly 1 http://wordpress.org/?v=3.3.1 By: hank https://www.habitablezone.com/2014/12/12/rosetta-pours-cold-water-on-cometary-origins-of-earths-oceans/#comment-32114 hank Sun, 14 Dec 2014 05:06:41 +0000 https://www.habitablezone.com/?p=48333#comment-32114 There's no reason different parts of the original solar nebula couldn't have had different isotopic abundances. So, the earth and this comet formed from different parts of the nebula, the H/D abundances would certainly be different if we assumed the original nebula was heterogeneous, and had been enriched by numerous primordial supernova explosions, solar winds and other local events, then poorly mixed. It is no more unreasonable that the comet and earth formed from different parts of the cloud than to assume different comets formed from different parts of the cloud. It is also possible that some as yet unknown mechanism tended to concentrate, or to favor accumulation of material of specific abundance ratios at different times or places, or perhaps Earth collided with and absorbed a planetesimal with a highly skewed H/D ratio. The original cloud was probably chemically chaotic and evolving, and exhibited all sorts of chemical gradients and concentrations. We know meteors and planetoids divide themselves into distinct families by mineral composition, and different minerals may exhibit different water content or sort themselves by isotopic abundance because they have different origins. Mineral-forming processes are influenced by both physical conditions and chemistry, neither of which distinguishes much between isotopes of the same element. But deuterium and hydrogen differ significantly in atomic weight (by a factor of two!) It is not unreasonable to suspect some physical process which affects the two quite differently. Until we examine lots of comets and other Oort Cloud objects, as well as other solar system planets and planetoids, speculations in this area may be a bit premature. There’s no reason different parts of the original solar nebula couldn’t have had different isotopic abundances. So, the earth and this comet formed from different parts of the nebula, the H/D abundances would certainly be different if we assumed the original nebula was heterogeneous, and had been enriched by numerous primordial supernova explosions, solar winds and other local events, then poorly mixed. It is no more unreasonable that the comet and earth formed from different parts of the cloud than to assume different comets formed from different parts of the cloud.

It is also possible that some as yet unknown mechanism tended to concentrate, or to favor accumulation of material of specific abundance ratios at different times or places, or perhaps Earth collided with and absorbed a planetesimal with a highly skewed H/D ratio. The original cloud was probably chemically chaotic and evolving, and exhibited all sorts of chemical gradients and concentrations. We know meteors and planetoids divide themselves into distinct families by mineral composition, and different minerals may exhibit different water content or sort themselves by isotopic abundance because they have different origins.

Mineral-forming processes are influenced by both physical conditions and chemistry, neither of which distinguishes much between isotopes of the same element. But deuterium and hydrogen differ significantly in atomic weight (by a factor of two!) It is not unreasonable to suspect some physical process which affects the two quite differently.

Until we examine lots of comets and other Oort Cloud objects, as well as other solar system planets and planetoids, speculations in this area may be a bit premature.

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