# Hydrogen in chondrites: Influence of parent body alteration and 1 atmospheric contamination on primordial components

Lionel G Vacher, Laurette Piani, Thomas Rigaudier, Dorian Thomassin, Maxime Piralla, Yves Marrocchi

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## ► To cite this version:

Lionel G Vacher, Laurette Piani, Thomas Rigaudier, Dorian Thomassin, Maxime Piralla, et al. Hydrogen in chondrites: Influence of parent body alteration and 1 atmospheric contamination on primordial components. Geochimica et Cosmochimica Acta, 2020, 281, pp.53-66. 10.1016/j.gca.2020.05.007. hal-03009498

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Hydrogen in chondrites: Influence of parent body alteration and atmospheric contamination on primordial components

Lionel G. Vacher¹,²*, Laurette Piani¹, Thomas Rigaudier¹, Dorian Thomassin¹, Guillaume Florin¹, Maxime Piralla¹ & Yves Marrocchi¹

¹CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-lès-Nancy, F-54501, France

²Department of Physics, Washington University, St. Louis, St. Louis, MO, USA

*Corresponding author: l.vacher@wustl.edu

**Abstract**

Hydrogen occurs at the near percent level in the most hydrated chondrites (CI and CM) attesting to the presence of water in the asteroid-forming regions. Their H abundances and isotopic signatures are powerful proxies for deciphering the distribution of H in the protoplanetary disk and the origin of Earth's water. Here, we report H contents and isotopic compositions for a set of carbonaceous and ordinary chondrites, including previously analyzed and new samples analyzed after the powdered samples were degassed under vacuum at 120°C for 48 hours to remove adsorbed atmospheric water. By comparing our results to literature data, we reveal that the H budgets of both H-poor and H-rich carbonaceous chondrites are largely affected by atmospheric moisture, and that their precise quantification requires a specific pre-degassing procedure to correct for terrestrial contamination. Our results show that indigenous H contents of CI carbonaceous chondrites usually considered the more hydrated meteorites are almost a factor of 2 lower than those previously reported, with uncontaminated D/H ratios differing significantly from that of Earth's oceans. Without pre-
37 degassing, the H concentrations of H-poor samples (e.g., CVs chondrites) are also affected by 38 terrestrial contamination. After correction for contamination, it appears that the amount of 39 water in chondrites is not controlled by the matrix modal abundance, suggesting that the 40 different chondritic parent bodies accreted variable amounts of water-ice grains. Our results 41 also imply that (i) thermal metamorphism play an important role in determining the H content 42 of both CV and ordinary chondrites but without affecting drastically their H isotopic 43 composition since no clear D enrichment is observed with the increase of petrographic type 44 and (ii) the D enrichment of ordinary chondrites does not result from the loss of isotopically 45 light H₂ induced by metal oxidation but is rather linked to the persistence of a thermally 46 resistant D-rich component. 47

# 1. Introduction

49

Hydrogen is the most abundant element in the solar system, but is present in only 50 minor to trace amounts in asteroids and planetary bodies. Throughout the solar system and its 51 history, H has occurred in various species, most commonly (i) H₂ in the gas phase, (ii) H₂O 52 molecules mostly as vapor and ice, (iii) OH⁻ or H₂O in silicate minerals, melts, and glasses, 53 (iv) C-bonded H in organic compounds and (v) minor volatile species, such as NH₃ and H₂S. 54

Today, water is present as ice, vapor, and/or liquid on Earth and other planets, dwarf planets, 55 moons, and comets. The presence of OH⁻ or H₂O in the silicate minerals comprising primitive 56 meteorites attests to the past existence of water on their asteroidal parent bodies and 57 constitutes an invaluable record of the distribution and composition of water in the 58 protoplanetary disk. 59

60

The H isotopic composition of water (expressed as D/H or per-mil deviations relative 61 to Vienna standard mean ocean water, VSMOW, as δD = [(D/H<sub>sample</sub>/D/H<sub>VSMOW</sub>) − 1] × 1000,
where $D/H_{VSMOW} = 155.76 \times 10^{-6}$) in planetary objects is generally thought to increase with increasing heliocentric distance, from $H_2O$ that was in isotopic exchange with D-poor $H_2$ near the sun ($D/H \approx 21 \times 10^{-6}$; Geiss and Gloeckler, 2003), to intermediate $D/H$ ratios in inner solar system objects (e.g., Earth's ocean, $D/H \approx 156 \times 10^{-6}$), to D-enriched outer solar system objects such as comets ($D/H$ up to $530 \times 10^{-6}$ in comet 67P/Churyumov-Gerasimenko; Altwegg et al., 2014). Determining the precise abundances and isotopic compositions of H in meteorites—as representative samples of asteroids—is thus of fundamental importance for understanding the source(s) of water in the asteroid-forming regions (Alexander et al., 2012; Piani et al., 2015, 2018; Piani and Marrocchi, 2018) and potential radial mixing during the evolution of the protoplanetary disk (Vacher et al., 2016; Piani et al., 2018).

The origin of water on Earth and other telluric planets is also a long-standing question (Alexander, 2017; McCubbin and Barnes, 2019). Although it is commonly assumed that the building blocks of the terrestrial planets derived from a cosmochemical reservoir best represented by enstatite chondrites, they accreted in a region where temperatures were too high for water and other volatiles to condense (Albarede, 2009). Therefore, these bodies are expected to be highly volatile-depleted, though they have tenuous atmospheres and water is largely present on Earth and Mars (Taylor, 2013), and possibly in the Venusian and Mercurian atmospheres (Smrekar and Sotin, 2012). For Earth, this paradox is generally bypassed by invoking the late accretion of 1–4 wt% of hydrated carbonaceous chondrites (i.e., CI-CM chondrites), which arrived at Earth due to the formation and subsequent migration of Jupiter (Morbidelli et al., 2000; Marty, 2012; Marty et al., 2016; Raymond and Izidoro, 2017).

Such a conclusion is highly dependent on our ability to precisely quantify the bulk H contents and $D/H$ ratios of extraterrestrial materials. This point is not trivial since, despite being commonly measured, H is the most prone **element** to terrestrial contamination (except for noble gases; Protin et al., 2016). For instance, it was recently shown that Martian
87 meteorites suffer rapid (<1 yr) terrestrial weathering and contamination that largely affect the
88 water contents and H isotopic compositions of minerals exposed at their surface (Stephant et
89 al., 2018). Moreover, water and volatile hydrocarbons (CH₂ and CH₃) quickly adsorb onto
90 rock surfaces, raising potential H and C contamination issues during sample preparation
91 (Salisbury et al., 1991). This implies that the H budget estimated for a given meteorite is a
92 complex mixture between indigenous hydrogen in minerals and organics and exogenous H
93 due to terrestrial weathering and adsorption. Corrections for exogenous H could be achieved
94 by performing (i) stepwise heating measurements to decipher between adsorbed, alteration,
95 and indigenous water (Robert and Epstein, 1982; Kerridge, 1985) or (ii) sample degassing
96 under vacuum at low temperature (e.g., Vacher et al., 2016). Bulk H budget reconstructions
97 from stepwise heating experiments are difficult due to the presence of different water-bearing
98 minerals characterized by variable contamination susceptibilities that release adsorbed water
99 at various temperatures. Furthermore, there is no consensus on a procedure to remove
100 adsorbed water from both terrestrial and extraterrestrial materials, and different studies have
101 employed various temperatures (70-350 °C) and durations (2-480 h) of heating under
102 vacuum (Savin and Epstein, 1970; Girard et al., 2000; Gong et al., 2007; Lupker et al., 2012).
103 Of note, a recent estimation of the bulk H contents and isotopic compositions of a large set of
104 chondrites was performed without a pre-degassing protocol (Alexander et al., 2012), and
105 therefore may have overestimated the H budget of primitive meteorites. In addition to
106 terrestrial contamination, meteorites experienced parent-body alteration processes
107 (hydrothermal alteration and thermal metamorphism; Brearley, 2006; Huss et al., 2006;
108 Marrocchi et al., 2018) whose influence on their pre-accretion H characteristics remains
109 unclear.

110 Here, to better understand the origin of hydrogen accreted by chondrites, we report the
111 H concentrations and isotopic compositions of a large set of carbonaceous and ordinary
112 chondrites. To test the influence of laboratory pre-degassing temperature, we selected 113 chondrites that have been previously characterized (C2-ung. = Tagish Lake; CI = Orgueil and 114 Alais; CY = Yamato 980115; King et al., 2019a; CM = Murchison, Mighei, and Murray; CV 115 = Allende, Bali, Grosnaja, Kaba, and Vigarano; Robert and Epstein, 1982; Kerridge, 1985; 116 Pearson et al., 2001; Alexander et al., 2012). As CM chondrites represent 25% of all 117 carbonaceous chondrite falls (Gounelle et al., 2005), several new CMs have recently been 118 described. We thus report the H concentrations and isotopic compositions of new CM falls 119 (Aguas Zarcas, Maribo and Munkundpura; Haack et al., 2012; Rudraswami et al., 2019) and 120 finds (Lonewolf Nunataks (LON) 94101 and Jbilet Winselwan; Lindgren et al., 2013; King et 121 al., 2019b). In addition, several ordinary chondrites and a CK-type carbonaceous chondrite 122 covering the entire range of thermal metamorphism (Tait et al., 2014) were analyzed to test 123 the influence of parent-body metamorphism on H characteristics (L3 = Grosvenor Mountains 124 (GRO) 95502, CK4 = Karoonda, L4 = Saratov, LL/L4 = Bjurbole, H4 = Sainte Marguerite, 125 and H6 = Kernouve). We use our results to discuss the nature of primordial components 126 accreted by chondrites and the influence of post-accretion effects, either in asteroidal bodies 127 or at Earth's surface. 128
## 2. Materials and method

135

### 2.1 Bulk measurements of H contents and isotope compositions

137

Hydrogen concentrations, [H], and isotopic compositions, D/H, of the different meteoritic samples were determined on-line using the Thermo Scientific EA IsoLink - deltaV IRMS System at CRPG laboratory (Nancy, France) according to the procedure developed by Lupker et al. (2012). First, meteoritic samples were crushed into powder in an agate mortar, weighed in tin capsules (CM, CI, CY and Tagish Lake: 1–3 mg; CV, CK, and OC: 4–10 mg), and the samples and capsules were loaded into a sample carrousel and degassed under vacuum at 120 °C for 48 h in a degassing canister (Lupker et al., 2012; Gaudin et al., 2015; Fig. 1A); degassing for less than 48 h was shown to result in increased variability of water contents and isotopic compositions due to remaining absorbed water (Lupker et al., 2012). After dehydration, the degassing canister was opened in a dry, N₂-flushed glove box and the sample carrousel was transferred into a sealed auto-sampler initially pre-flushed with He (Fig. 1B). The auto-sampler was then connected to the EA and pumped out during 20 min before opening it to the reduction column as a precautionary step to suppress any potential rehydration of the samples in the event of atmospheric contact between degassing and analysis.

The samples were combusted at 1450 °C (**required temperature to ensure rapid sample reduction and to prevent any CH₃ formation**) on a glassy carbon reaction tube filled with glassy carbon chips and itself placed into a ceramic liner to reduce hydroxyls (OH) **released by the samples into H₂ according to the reaction: 2OH + C (unlimited in reactor) → 2CO + H₂** (Fig. 1C). The produced gases were separated on a chromatographic column maintained at 60 °C and the extracted H₂ was introduced into the mass spectrometer through an open-split and
its D/H isotopic composition **was** analyzed (Fig. 1D). The extracted H₂ was corrected for H₃⁺ contributions using in-house H₂ standard injections and [H] and D/H were determined by comparison with seven internal standards routinely included during the analyses: (i) phlogopite (Mica-Mg, 0.29 wt.% H, D/H = 143.8 × 10⁻⁶), (ii) muscovite (MuscD65, 0.474 wt.% H, D/H = 142.6 × 10⁻⁶), (iii) a fine-grained marine sediment from the Bay of Bengal (SO188, 0.489 wt.% H, D/H = 142.7 × 10⁻⁶), and (iv) four basalts with different H concentrations (CYP78, 0.14 wt.% H; JB3-GSJ, 0.20 wt.% H; SR2-02, 0.27 wt.% H; and GMR-KS12, 0.42 wt.% H). Errors on hydrogen concentrations, calculated as twice the standard deviation divided by the average, increase with decreasing standard water content following the negative power law 2SD / [H] = 0.05 × [H]⁻⁰.⁴³, which was used to estimate the 2σ sample errors reported in Table 1. Hydrogen isotopic compositions are reported as D/H ratios or as δD values (‰) relative to VSMOW. The reproducibility of this method is better than 15% (2σ) for [H] and 0.5 × 10⁻⁶ for D/H (or 5‰ for δD).

172

2.2 Bulk measurements of C and N concentration and isotopic compositions

174

Carbon and nitrogen concentrations ([C] and [N], respectively) and carbon isotopic compositions (δ¹³C, ¹³C/¹²C variations reported relative to Vienna Pee Dee Belemnite, VPDB, where ¹³C/¹²C<sub>VPDB</sub> = 0.01123720) of the different meteoritic samples were determined on-line using the Thermo Scientific EA IsoLink - deltaV IRMS System at the CRPG laboratory. Samples were crushed into fine powder and wrapped in tin capsules (2–29 mg). The capsules were loaded in a specific auto-sampler connected to the EA and pumped out during 20 min before opening it to the oxidation column. Samples were then **introduced into an oxidation reactor made** of a quartz tube filled with chromium oxide, pure copper, and silvered cobalt oxide **and heated at 1020 °C**. A controlled pulse of oxygen causes the oxidation of tin
capsules leading to an exothermic reaction that raises the sample temperature to about 1800°C. The produced gases (N₂, CO₂) were separated on a chromatographic column maintained at 70 °C and the carbon isotopic composition of the extracted CO₂ was measured with a Thermo Scientific Delta V Advantage continuous flow IRMS. Carbon isotopic composition were determined by comparison with two internal and two international standards routinely included during the analysis: (i) BFSd (δ¹³C = -21.5‰), (ii) CRPG_M2 (δ¹³C = -24.98‰), (iii) NBS22 (δ¹³C = -30.03‰) and (iv) USGS24 (δ¹³C = -16.1‰). Values are quoted in the delta notation in ‰ relative to V-PDB and the reproducibility was better than 0.2‰. Four internal standards were used to calculate [N] and [C]: (i) BFSd (0.53 wt.% C), (ii) CRPG_M2 (0.408 wt.% C), (iii) Eurovector Synthetic Soil Mix #1 (0.216 wt.% N, 3.5 wt.% C) and (iv) Eurovector Synthetic Soil Mix #4 (0.048 wt.% N, 2.417 wt.% C). Errors (2σ) on [N] are estimated to be 10% and 30% for samples containing more and less than 0.08 wt.% N, respectively. For carbon analyses, 2σ errors are expected to be 2% for [C] and 2‰ for δ¹³C.

198
## 3. Results

### 3.1 Hydrogen characteristics of chondrites

Results from hydrogen extractions and associated D/H isotopic analyses are presented in Table 1 and Figure 2. For most samples (excluding C2-ung. Tagish Lake and CI Alais for their D/H variability), replicate aliquots of the same meteorite exhibit good reproducibility, with 2σ standard deviations less than 15% for [H] and 5‰ for δD.

Hydrogen abundances of CI, CY and CM chondrites vary widely, but exhibit comparable ranges, from 0.47 to 1.01 wt.% H (Fig. 2A). The lowest hydrogen contents were measured in CM Jbilet Winselwan, possibly due to dehydration during parent-body metamorphism (King et al., 2019b). CMs are depleted in deuterium compared to CIs ($D/H_{CM} = 131-170 \times 10^{-6}$ vs. $D/H_{CI} \approx 177 \times 10^{-6}$) but show similar range of D/H values as the CY Antarctica Y-980115 ($D/H_{CY} = 139 \times 10^{-6}$, Fig. 2B). The low hydrogen content of Y-980115 (0.71 wt.% H) relative to CI-CM chondrites and its D-poor isotopic composition might be might be a consequence of (i) thermal metamorphosed at temperature > 500°C (King et al., 2019a) and/or (ii) terrestrial weathering (e.g., Alexander et al., 2018a). The ungrouped C2 carbonaceous chondrite Tagish Lake exhibits a hydrogen content similar to the lowest value measured for CM chondrites (0.43 wt.% H), but this unique carbonaceous chondrite is the most D enriched ($D/H = 225 \times 10^{-6}$, Fig. 2A and B), consistent with previous measurements (Pearson et al., 2001; Alexander et al., 2012). CV chondrites (0.06-0.19 wt% H, Fig. 2A) contain lower hydrogen concentrations than CM and CI chondrites, whereas their hydrogen isotopic compositions are highly variable ($D/H = 139-161 \times 10^{-6}$, Table 1) over a range similar to that of CM chondrites (Fig. 2B). Ordinary chondrites and CK-type carbonaceous chondrites present the lowest hydrogen concentrations (≤0.03 wt.% H, excluding Grosvenor
224 Mountains (GRO) 95502, an Antarctic find possibly affected by terrestrial weathering; Fig.

225 2A), and have relatively D-poor hydrogen isotopic compositions (D/H = 134-144 × 10⁻⁶, Fig.

226 2B).

227

228 3.2 Nitrogen and carbon characteristics of chondrites

229

230 Table 2 summarizes the carbon and nitrogen contents and carbon isotopic

231 compositions of the analyzed chondrites. CI, CY and CM chondrites contain the highest N

232 and C contents in this study, with 0.09-0.17 wt.% N and 1.54-3.04 wt.% C in CMs and 0.09-

233 0.21 wt.% N and 3.06-3.35 wt.% C in CIs (Fig. 3). They both show comparable ranges of

234 carbon isotopic compositions, with δ¹³C ranging from -16 to -13‰ and -14 to -4‰ for CIs

235 and CMs, respectively. The nitrogen and carbon concentrations in Tagish Lake (0.11 wt.% N

236 and 2.14 wt.% C) are comparable to those in CM chondrites, but with a more ¹³C-enriched

237 isotopic composition (δ¹³C ≈ +5‰). Compared with these C- and N-rich chondrites, CV, CK,

238 and ordinary chondrites are depleted in N (≤0.03 wt.%) and C (≤1.42 wt.%), and have lower

239 carbon isotopic compositions than hydrated chondrites, with δ¹³C ≈ -27 to -18‰.

240

241

242
243 **4. Discussion**

244

245 **4.1 Effect of terrestrial contamination in carbonaceous chondrites**

246

247 **4.1.1 Influence of pre-degassing temperature on the total H budget**

248

249 Immediately after falling to Earth's surface, meteorites are exposed to terrestrial
250 moisture and precipitation that could significantly affect their H characteristics, even in dry
251 environments such as hot deserts (Stephant et al., 2018). Consequently, bulk meteorite H
252 budgets are complex mixtures of indigenous hydrogen, terrestrial weathering, and adsorbed
253 water hosted by different minerals/phases with variable thermal behaviors.
254 Thermogravimetric analysis and derivate curves obtained in the range 25-1200 °C (Garenne
255 et al., 2014; King et al., 2015; Gilmour et al., 2019) suggest a complex thermal evolution of
256 H-bearing phases with the following release temperatures: (i) 25-200 °C for absorbed H₂O,
257 (ii) 200-400 °C for water in hydroxides and H-bearing organic matter, (iii) 400-770 °C for
258 OH⁻ in phyllosilicates, and (iv) 770-900 °C for H₂O in sulfates. Although suspected to occur
259 to some degree at 200-400 °C, it has been proposed that adsorbed terrestrial water is mainly
260 released from hydrated carbonaceous chondrites at 25-250 °C (Boato, 1954; Kerridge, 1985;
261 Baker et al., 2002; Garenne et al., 2014; Gilmour et al., 2019).

262 Alexander et al. (2012, 2013) reported H concentrations and isotopic compositions for
263 a large set of carbonaceous chondrites that were stored in desiccators at room temperature for
264 days to weeks prior to analyses. Their data define a positive correlation in a D/H vs. 1/H
265 diagram (Fig. 4) that reveals the increasing contribution of H-bearing, D-rich, insoluble
266 organic matter (IOM; Alexander et al., 2007; Alexander et al., 2012) to the total H budget, the
267 largest contributions coming from phyllosilicates in hydrated chondrites. Our data define a
similar positive trend, but with a statistically different slope (Fig. 4) that reveals the influence of the pre-degassing temperature on observed meteorite H features. Thereby, our bulk H measurements of samples also measured by Alexander et al. (2012) demonstrate that pre-degassed CM and CI chondrites contain ~10–30% and ~40% less H, respectively, than non-degassed samples (Fig. 4). Several reasons can be invoked to explain such important differences: (i) the significant loss of indigenous hydrogen induced by the pre-degassing protocol, leading to an underestimated H budget, (ii) sample heterogeneity, the effects of which are apparent due to the small amounts of material analyzed, and/or (iii) the intended removal of absorbed terrestrial water.

To test these different scenarios, we estimated the H isotopic composition of the hydrogen lost during pre-degassing at 120 °C for 48 h using the following mass balance equation:

$$ [H]_{\text{lost}} \times D/H_{\text{lost}} = [H]_{25^{\circ}\text{C}} \times D/H_{25^{\circ}\text{C}} - [H]_{120^{\circ}\text{C}} \times D/H_{120^{\circ}\text{C}} \quad (1) $$

where [H]$_{25^{\circ}\text{C}}$, [H]$_{120^{\circ}\text{C}}$, D/H$_{25^{\circ}\text{C}}$, and D/H$_{120^{\circ}\text{C}}$ correspond to the bulk H concentrations and isotopic compositions of the samples determined at room temperature (i.e., 25 °C) and after pre-degassing at 120 °C for 48 h, respectively. The hydrogen lost during pre-degassing corresponds to [H]$_{lost}$ = [H]$_{25^{\circ}\text{C}} - [H]$_{120^{\circ}\text{C}}$. Consequently, if the H lost during pre-degassing was adsorbed terrestrial water, its calculated H isotopic composition should be (i) similar from one sample to the next and (ii) within the range of terrestrial values. On the other hand, large H isotopic variations are expected if the H lost resulted from sample heterogeneity or the removal of indigenous hydrogen. The H isotopic compositions of pre-degassed H range from D/H ~ 150–155 × 10$^{-6}$ for Murchison, Mighei, Murray, and Orgueil. These values are in the range of H isotopic ratios reported for terrestrial hydrosphere reservoirs (115–165 × 10$^{-6}$;
Lécuyer et al., 1998; Frankenberg et al., 2009; Clog et al., 2013), but differ strongly from the
(i) D-poor phyllosilicates that bear the signature of asteroidal water in CM and CI chondrites
(D/H ~ 85–125 × 10⁻⁶; Alexander et al., 2012; Piani et al., 2018, 2019) and (ii) D-rich organic
matter (D/H ~ 265–310 × 10⁻⁶; Alexander et al., 2007). Consequently, we interpret the
differences in H concentrations obtained with and without the pre-degassing routine as mostly
due to contamination of primitive meteorites by atmospheric moisture. This scenario cannot,
however, explain the D/H ratio calculated of the H degassed from LON 94101, which display
a significantly higher D/H value compared to the other common samples (~ 400 × 10⁻⁶). By
analogy with other CM chondrites, the removal of indigenous H during pre-degassing would
result in a D-poor signature for [H] lost, at odds with our calculations. Alternatively, the
preferential degassing of H from D-rich IOM or H-bearing organic compounds (i.e., small
hydrocarbons or molecules found in the soluble part of the meteoritic organic matter) might
explain such high D/H values and contributed to the H budget removed during our pre-
degassing procedure. However, given that (i) the H isotopic compositions of [H] lost are D-poor
compared to organic molecules in carbonaceous chondrites (Pizzarello et al., 1994; 2006;
Yamashita & Naraoka, 2014), (ii) stepwise pyrolysis performed by Robert and Epstein (1982)
on Murchison and Murray indicates that only few amount of carbon (~ 0.2 mol% of the total
C) were lost compared to water below 200 °C (11.5 and 10.8 mol% of the total H,
respectively), and (iii) the decomposition of IOM likely occurs at 200–500 °C (Gilmour et al.,
2019; Remusat et al., 2019), we concluded that the amount of indigenous organics volatile
lost during pre-degassing is not significant and the D-rich compositions of the [H] lost by LON
94101 is rather a consequence of sample heterogeneity (Lindgren et al., 2013).

315
316

## 4.1.2 Quantification of terrestrial contamination in carbonaceous chondrites

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

To estimate the influence of pre-degassing, we compare hydrogen concentrations and isotopic compositions measured in different studies for CI Orgueil and CM Murchison as a function of pre-degassing temperature. Murchison **shows** ~30% less H after pre-degassing at 200 °C compared to measurements performed without pre-degassing (Fig. 5A–C). Isotopically, **this sample does not** show a large change, with D/H value of ~150 × 10⁻⁶ (Fig. 5C). In contrast, a sample of Orgueil pre-degassed at 120–350 °C shows (i) a H loss of up to ~40–80% and (ii) a D/H increase up to ~190 × 10⁻⁶ relative to samples measured without pre-degassing (D/H ~ 150 × 10⁻⁶; Figs. 5B–D). This disparity between CM and CI chondrites probably derives from the fact that the bulk D/H values of CMs, which result from the combined contributions of D-poor water and D-rich OM, are fortuitously close to the D/H values imparted by atmospheric contamination (D/H<sub>CM</sub> ~ 142 × 10⁻⁶ vs. D/H<sub>[H] lost</sub> ~ 150 × 10⁻⁶), and contamination thus produces only minor changes. In contrast, water and OM in CIs are D-rich compared to CMs (Busemann et al., 2006; Alexander et al., 2007; Piani et al., 2018, 2019), with bulk H isotopic compositions (D/H<sub>CI</sub> ~ 177 × 10⁻⁶) markedly higher than that of the contaminating water. Consequently, the effects of atmospheric moisture are more perceptible in CIs than in CMs.

334

335

336

337

338

339

340

To better quantify the influence of terrestrial contamination, we compared [H]<sub>lost</sub> (= [H]<sub>25 °C</sub> – [H]<sub>120 °C</sub>) for different chondrites as a function of the H concentration determined after pre-degassing at 120°C. We thusly obtained **separate** linear trends for **CI**, **CM** and **CV** carbonaceous chondrites, indicating that meteorites containing more H are more prone to contamination (Fig. 6). Interestingly, CM- and CI-type chondrites seem to define a single trend (r² = 0.70; MSWD = 1.5), **suggesting that CIs would be more** affected by H contamination than CMs (Fig. 6). The H concentrations of Tagish Lake are highly
341 heterogeneous (H = 1.37 and 0.85 wt.%, from Pearson et al., 2001, and Alexander et al., 2012, respectively) and have been shown to depend strongly on the studied lithology (H = 0.74–0.94 wt.%; Alexander et al., 2012); however, as we do not have the petrological details of the Tagish lake pieces measured in our study, we omit Tagish Lake from further discussion.

346 The difference in the amount of H loss between CI and CMs probably reflects 347 secondary mineralogical diversity between these two groups of chondrites (Fig. 6). CI 348 chondrites are mainly dominated by serpentine and saponite minerals, the latter being clay 349 minerals with the capacity to absorb significant amounts of water into their inter-layers 350 (Tomeoka and Buseck, 1988; King et al., 2015). Thus, it is likely that CI chondrites contains 351 indigenous inter-layer water that could be removed alongside with terrestrial water during 352 pre-degassing, leading to an underestimation of the H budget in CI chondrites. Nevertheless, 353 it appears that the high abundance of inter-layer water in Orgueil is probably related to its 354 long residence time on Earth (since 1864) and it is likely that this meteorite was devoid of 355 inter-layer water prior to its arrival on Earth (Baker et al., 2002). In addition, stepwise heating 356 performed on Orgueil demonstrated that water released at temperature lower than 200 °C is 357 characterized by terrestrial-like values (i.e., Δ¹⁷O = 0 ‰ and D/H = 153 × 10⁻⁶), supporting 358 that only minor indigenous water was present in the inter-layers of Orgueil (Robert and 359 Epstein, 1982; Baker et al., 2002). In contrast, CM chondrites are almost saponite-free, and 360 are instead dominated by Fe-Mg-rich serpentine that retains less absorbed water in its silicate 361 layers than saponite (Barber 1981; Howard et al., 2015). It is unclear why the CV trend is 362 separate from the CI-CM trend, but the amount of H lost during pre-degassing suggests that 363 this group of chondrites is also very sensitive to terrestrial alteration and can absorb similar H 364 proportions as CM chondrites (Fig. 6). Phyllosilicates are modally less abundant in CV (up to 365 4 vol.%; Howard et al., 2010) than in CM chondrites (~75 vol.%; Howard et al., 2015).
Assuming that phyllosilicates are the main storage sites for atmospheric moisture in hydrated carbonaceous chondrites, water adsorption should be vastly lower in CV than in CM chondrites (even accounting for the mineralogical differences of their phyllosilicates).

Alternatively, CI and CM phyllosilicates are almost water saturated—i.e., their water adsorption capacity is limited—whereas CV phyllosilicates, despite being less abundant, have more adsorption sites available for accommodating atmospheric moisture. Whatever the reason, it is apparent that terrestrial contamination can greatly affect the H budgets of the most H-poor (CV-like) and H-rich (CI-like) chondrites alike (Figs. 5 and 6). The bulk H contents and D/H ratios of chondrites should thus be measured after pre-degassing under vacuum at ≥120 °C. The consequences of correcting the H compositions of chondrites for terrestrial contamination are discussed in §4.3.

377

## 4.2 The influence of thermal metamorphism

379

### 4.2.1 CV-type carbonaceous chondrites

381

CV chondrites are divided into three subgroups partly reflecting their various aqueous and thermal alteration histories: reduced, $CV_{Red}$; oxidized Allende-like, $CV_{OxA}$; and oxidized Bali-like, $CV_{OxB}$. Of the oxidized CVs, the $CV_{OxB}$ subgroup is the most extensively altered and contains abundant phyllosilicates and chondrules replaced by phyllosilicates and magnetite. In contrast, the $CV_{OxA}$ and $CV_{Red}$ subgroups contain minor phyllosilicates and abundant Ca-Fe-rich secondary phases such as andradite, hedenbergite, and kirschsteinite (Krot et al., 2004; Brearley, 2006; Howard et al., 2010; Ganino and Libourel, 2017). CV3s have experienced various degrees of metamorphism that are partly overprinted by subsequent aqueous alteration and further obscured by brecciation (Bonal et al., 2006). Based on the
maturation grade of their organic matter, Bonal et al. (2006) assigned a range of petrographic degrees for the CV chondrites Kaba (~3.1), Vigarano (3.1–3.4), Bali and Grosnaja (~3.6), and Allende (>3.6), although they highlighted the occurrence of clasts of different petrologic types within individual meteorites (e.g., Bali). The H-, C-, and N-concentrations and isotopic compositions measured for these CV chondrites reflect the complex inputs of brecciation and aqueous and thermal alteration, with no clear behavior of these elements and isotopes with increasing petrologic type (Figs. 6 and 7a; Tables 1 and 2). Nevertheless, the most metamorphosed $CV_{OXA}$, Allende, presents the lowest H concentrations, with its most H-depleted lithologies (Yang and Epstein, 1983) having similar H contents as the metamorphosed CK4 Karoonda (Fig. 7a). This result suggests that thermal metamorphism of CV chondrites could induce a significant H loss for petrologic types >3.6 (Fig. 7a).

402

403 4.2.2 Ordinary chondrites

404

Ordinary chondrites (OCs) from the H, L, and LL groups exhibit pervasive imprints of thermal metamorphism and, to a lesser degree, aqueous alteration. Semarkona (LL3.00) and Bishunpur (LL3.15) are among the rare unequilibrated OCs to contain hydrated minerals (smectites) and other secondary phases (calcites) thought to have formed on their parent body from an oxidizing fluid (Alexander et al., 1989). Water measured in these chondrites is enriched in D, as attested by (i) their bulk D/H values up to $600 \times 10^{-6}$ (McNaughton et al., 1982; Yang and Epstein, 1983) and (ii) *in-situ* measurements of D/H values up to $1800 \times 10^{-6}$ (Deloule and Robert, 1995; Piani et al., 2015). Such high D enrichments were interpreted either as inherited from the accretion of D-rich ice that originated in cold regions of the solar system (Deloule and Robert, 1995; Piani et al., 2015) or as the result of parent-body processes (Alexander et al., 2012). Bleached chondrules found in LL3, L3, and more rarely in H3

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411

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413

414

415
416 chondrites attest that aqueous alteration was widespread in OCs, but was mostly erased by 417 subsequent thermal metamorphism (Grossman et al., 2000). This later metamorphic event 418 resulted in high degrees of equilibration of the three OC sub-groups spanning petrological 419 types 3–7 and equilibration temperatures up to 1000 °C (Tait et al., 2014).

420 The five OCs measured herein span the range of H concentrations reported in OCs, 421 with the most metamorphosed chondrites (H6 Kernouve) being the most depleted in hydrogen 422 (Fig. 7B). These five OCs exhibit D/H ratios similar to those previously measured in 423 equilibrated ordinary chondrites (~130–160 × 10⁻⁶), and we observe no strong differences 424 between groups or petrological types (Fig. 7B). Furthermore, we do not observe D 425 enrichments with increased parent-body thermal metamorphism (Fig. 7B), in agreement with 426 previous observations (Robert et al., 1979; McNaughton et al., 1982). This is at odds with the 427 assumption that water in ordinary chondrites became increasingly enriched in deuterium due 428 to the oxidation of iron and subsequent loss of isotopically light H₂ (Alexander et al., 2010, 429 2012; Sutton et al., 2017). This assumption was initially proposed to explain the deuterium 430 enrichment of IOM in OCs with increasing degree of metamorphism, the organic matter 431 thereby being enriched by isotopic exchange with the remaining D-rich water (Alexander et 432 al., 2010). However, given that both the remaining water and OM should have been enriched 433 in D by this process, the bulk D/H ratios of OCs should increase with increasing degree of 434 thermal metamorphism. The absence of such D enrichments in the bulk chondrites thus 435 contradicts the implication of water in the D enrichment of the OM, instead supporting the 436 proposal that ordinary chondrites contain a thermally recalcitrant D-rich organic matter 437 component (Remusat et al., 2016). Overall, thermal metamorphism in OCs seems to have 438 mainly decreased the bulk-rock hydrogen contents without strongly influencing the hydrogen 439 isotopic ratios for petrological types ≥3.2 (Fig. 7B).
440

441

442

443

444

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446

447

448

449

The percentage of fayalite (%Fa) in ordinary chondrites increases from H to L to LL groups and is considered a robust proxy of the degree of hydration (i.e., the water content) of their respective parent bodies (Rubin, 2005; Florin et al., 2020). However, the lack of variation between the H contents of the different groups of OCs (Fig. 7B) suggests that they could have accreted similar amounts of water. This could be interpreted as evidence for pre-accretion hydration processes in different regions of the protoplanetary disk. Whereas there is no clear limit between the H contents of unequilibrated and equilibrated OCs, the observed decrease in H contents with increasing metamorphism is in line with the progressive increase of %Fa and the loss of Fe-Ni metal during metamorphism (Florin et al., 2020).
450 4.3 Implication for the origin and abundance of H in chondrites

451

452 Our data suggest that terrestrial contamination can represent a significant part of the
453 measured chondritic H budget, which strongly depends on the analytical protocol and
454 particularly the pre-degassing procedure. The effects of terrestrial contamination are
455 especially important for **chondrites** with the **highest** indigenous hydrogen contents **within a given chondrite group** (Figs. 4 and 6). However, within errors, we observe similar positive
456 correlations and zero intercepts (D/H ~ 100 × 10⁻⁶ or δD ~ -400‰) between D/H and C/H for
457 CMs (Fig. 8) as previously reported (Alexander et al., 2012). These values represent the
458 isotopic composition of water accreted by the CM parent body (Alexander et al., 2012). This
459 similarity indicates that previous estimations of the D/H ratios of water in the region of CM
460 parent-body accretion (Alexander et al., 2012) were not significantly affected by terrestrial
461 contamination, as also attested by the consistency with *in-situ* measurements via secondary
462 ion mass spectrometry (SIMS; Piani et al., 2018). The D/H ratio of water accreted by CV
463 chondrites was only estimated recently from SIMS measurements (Piani and Marrocchi,
464 2018), and our bulk data confirm their observation that CV water is enriched in deuterium
465 compared to CM water (Fig. 8). If CMs and CVs accreted beyond the orbit of Jupiter as
466 commonly proposed (Kruijer et al., 2017; Nanne et al., 2019), this suggests the existence of
467 different water-ice reservoirs, with CV water being enriched in heavy H and O isotopes (Piani
468 et al., 2018; Piani and Marrocchi, 2018; Marrocchi et al., 2018).
469

470 Among chondrites, CIs are of primary importance as their bulk chemical compositions
471 are similar to that of the solar photosphere, which is representative of the average solar system
472 composition (Lodders, 2003). In addition, CIs are generally considered to be the most
473 hydrated chondrites based on previous H measurements (Pearson et al., 2001; Alexander et
474 al., 2012) and their high abundances of secondary minerals (~ 97%; King et al., 2015).
Although it remains a possibility that a small amount of the released water below 120°C could have been initially indigenous, our data reveal that CIs analyzed without pre-degassing are essentially contaminated by terrestrial moisture, and we estimate their indigenous water contents to be almost a factor of 2 lower than previously reported (0.93 wt.% H compared to 1.56 wt.% H; Pearson et al., 2001; Alexander et al., 2012), in agreement with results from stepwise heating analyses (Boato, 1954; Robert and Epstein, 1982; Yang and Epstein, 1983; Kerridge, 1985; Eiler and Kitchen, 2004). Consequently, CI chondrites have indigenous water contents similar to those estimated for CM chondrites, suggesting that CIs and CMs accreted similar proportions of water, although they contain vastly different proportions of matrix (65 vol.% and 100 vol.% in CMs and CIs, respectively; Alexander et al., 2018b and references therein). CV chondrites comprising 40 vol.% matrix have H abundances roughly one tenth those of CM and CI chondrites. Together, our results for CV-, CM-, and CI-type carbonaceous chondrites argue against the suggested dependency of the bulk H concentration on matrix content (Alexander et al., 2018b). Nevertheless, our data for C and N concentrations (Fig. 3) are consistent with a matrix content dependency for these elements (Alexander et al., 2018b). Furthermore, correcting for terrestrial water contamination in CIs largely affects their D/H isotopic compositions, which is not the case for CMs (Fig. 5). This implies that CIs do not have H isotopic ratios as close to that of Earth's water as previously estimated based on measurements performed without pre-degassing. This conclusion was reported nearly 40 years ago (Robert and Epstein, 1982; Kerridge, 1985), but was overshadowed by recent studies that did not quantify the effects of terrestrial contamination (Alexander et al., 2012). Consequently, the large contamination of CI water and its non-terrestrial H isotopic composition should be accounted for in models of Earth's formation based on the mixing of chondrite-like materials, as considering CIs as the putative source of Earth's oceans would also affect the ⁵⁴Cr mass balance calculation (Warren, 2011; Dauphas,
500

2017). In such a framework, CM chondrites thus appear to be the most isotopically similar extraterrestrial materials to the Earth's surficial hydrogen reservoir.

501

502

503

## 5. Conclusions

504

505

We have determined the bulk hydrogen concentrations and isotopic compositions of a large set of chondritic samples (CI, CM, CV, CK, and ordinary chondrites) using an elemental analyzer coupled to an isotope ratio mass spectrometer. Samples were pre-degassed under vacuum at 120 °C for 48 h before measurements. Our main results are:

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509

1) CI and CM chondrites and Tagish Lake define a correlation in a D/H vs. 1/H diagram induced by the increasing contribution of insoluble organic matter to the total H budget. This trend is statistically distinct from that defined by similar chondrites analyzed without pre-degassing at ≥120 °C.

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513

2) No clear D enrichment is observed with the increase of parent-body thermal metamorphism for ordinary and CV-type carbonaceous chondrites.

514

515

From these results, we drew the following conclusions:

516

1) Chondrites are largely affected by terrestrial contamination, with the most hydrated

517

CI chondrites being the most prone to contamination because phyllosilicates are more abundant in CIs compared to CMs and CVs. After correction of contamination, the primordial

518

519

H contents of CI, CM, and CV chondrites are significantly lower than generally reported and is not related to their matrix modal abundance, implying that their respective parent bodies accreted variable amounts of water-ice grains.

520

521

522

2) The D/H ratio of Orgueil is affected by terrestrial contamination, leading to an important underestimation of its H isotopic composition. This result is important as it could

523
affects the amount of water delivery by CI chondrites in the models of Earth's formation
based on the mixing of chondrite-like materials.

3) Although based on a limited number of samples, thermal metamorphism suggests that significant H were lost in CVs of petrological type >3.6. It also decreased the H contents of ordinary chondrites, but minimally affected the D/H ratios of OCs of petrological type ≥3.2.

4) The absence of an increasing D/H ratio with increasing the metamorphism degree for bulk ordinary chondrites does not support models in which water became enriched in deuterium via the oxidation of iron and the loss of isotopically light H₂. On the contrary, this observation supports the presence of thermally resistant D-rich organic matter in ordinary chondrites.

535

536 Acknowledgments

537

We thank Mike Zolensky and Bernard Marty for providing samples. We also thank the
National Institute of Polar Research (Japan), the Natural History Museum of Denmark
(Copenhagen), the Muséum national d'Histoire naturelle (Paris, France), the Natural History
Museum of Vienna (Austria), and the Antarctic Search for Meteorites (ANSMET) program
for loaning samples. US Antarctic meteorite samples were recovered by ANSMET, funded by
NSF and NASA, and characterized and curated by the Department of Mineral Sciences of the
Smithsonian Institution and Astromaterials Curation Office at NASA Johnson Space Center.
This work was funded by l'Agence Nationale de la Recherche through grant ANR-14-CE33-
0002-01 SAPINS (PI Yves Marrocchi) and ANR-19-CE31-0027-01 HYDRaTE (PI Laurette
Piani) and by the European Research Council (PHOTONIS project, grant agreement No.
695618 to Bernard Marty). This is a CRPG contribution #2728.
549 **Research data**

550 Original data of this study are available in the supplementary file.

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773 Sutton S., Alexander C. M. O., Bryant A., Lanzirotti A., Newville M. and Cloutis E. A.

774 (2017) The bulk valence state of Fe and the origin of water in chondrites. *Geochim.*

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788 93–100.

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792 *Acta* **47**, 2199–2216.

793

794

795

796

797
798 **Figure captions**

799

800 Fig. 1. Schematic representation of the analytical protocol used in this study. The samples
801 were first degassed under vacuum at 120 °C for 48 h in a degassing canister (A) before being
802 transferred into a sealed auto-sampler pre-flushed with He (B). Samples were combusted at
803 1450 °C (C) and the extracted H₂ was introduced into the mass spectrometer through an open
804 split and its D/H isotopic composition analyzed (D).

805

806 Fig. 2. (A) Average bulk hydrogen and water abundances (wt.%) for the different groups of
807 chondrites analyzed in this study. Half-filled markers and unfilled triangle represent samples
808 presumably affected by terrestrial weathering **and/or** metamorphism dehydration (Jbilet
809 Winselwan, Y-980115 and Gro 95502). (B) Distribution of the H isotopic compositions (bulk
810 D/H ratios and equivalent δD values) of chondrites (n = 178). The upper part of the graph
811 presents the H isotopic compositions measured in this study for each group of chondrites, and
812 the lower part presents values reported in literature: Boato (1954), Robert (1978), Robert et al.
813 (1979), Kolodny et al. (1980), Kerridge (1985), McNaughton et al. (1982), Robert and
814 Epstein (1982), Yang and Epstein (1983), Robert (2003), Pearson et al. (2001), and Alexander
815 et al. (2012).

816

817 Fig. 3. Relationship between bulk carbon and nitrogen abundances (wt.%) for all chondrites
818 analyzed. A positive trend (solid black line) is observed between the two parameters, with an
819 R² value of 0.77 (MSWD = 1.7). Dashed curves represent the 95% confidence interval of the
820 regression (errors are 2σ).

821
Fig. 4. Bulk hydrogen abundances (expressed as 1/H) and D/H isotopic ratios of CM chondrites and the ungrouped Tagish Lake chondrite ('TL') from this study and Alexander et al. (2012) and CM Paris (Vacher et al., 2016). Two positive trends (solid lines) with distinct slopes but similar intercepts are observed for our data (red; D/H = 70 (± 17) × 1/H + 60 (± 24); 2σ, R² = 0.91, MSWD = 21) and the data from Alexander et al. (2012), excluding heated CMs (gray; D/H = 133 (± 28) × 1/H + 28 (± 26); 2σ, R² = 0.55, MSWD = 466). Dashed curves represent the 95% confidence intervals of the regressions (errors are 2σ).

Fig. 5. The effect of pre-degassing temperature on the measured (A, B) hydrogen abundances and (C, D) hydrogen isotopic compositions of CM Murchison (red) and CI Orgueil (orange). Measured hydrogen concentrations decrease and D/H ratios increase with increased pre-degassing temperature for Orgueil. Ranges of D/H values of D-rich organic matter (dark gray area; Alexander et al., 2007), D-poor phyllosilicates (light gray area; Alexander et al., 2012; Piani et al., 2018, 2019) and terrestrial hydrosphere (blue area; Lécuyer et al., 1998; Frankenberg et al., 2009; Clog et al., 2013) are also represented for comparison. Data from: Boato (1954), Kolodny et al. (1980), Robert and Epstein ('R&E', 1982), Yang and Epstein ('Y&E', 1983), Pearson et al. (2001), and Alexander et al. (2012).

Fig. 6. The amount of H lost during the pre-degassing procedure as a function of the indigenous H content measured in CV-, CM-, and CI-type carbonaceous chondrites after pre-degassing at 120 °C. The amount of pre-degassed H is calculated as the difference between the hydrogen content measured in our samples after pre-degassing at 120 °C and that measured in the same samples at room temperature (25 °C) using the same analytical technique, but without pre-degassing (Pearson et al., 2001; Alexander et al., 2012) (errors are 2σ).
847

848

Fig. 7. Bulk D/H ratios as a function of bulk hydrogen abundances (expressed as 1/H) for all reported analyses of (A) CV chondrites (this study; Boato, 1954; Robert and Epstein, 1982; Kerridge, 1985; Pearson et al., 2001; Alexander et al., 2012) and (B) ordinary chondrites (this study; Robert et al., 1979; McNaughton et al., 1982; Yang and Epstein, 1983; Alexander et al., 2012) (errors are 2σ).

849

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852

853

854

Fig. 8. Bulk hydrogen isotopic compositions of CV (black) and CM (red) chondrites as a function of their bulk C/H ratios. Delta notation is used for H isotopic compositions to facilitate comparison with Alexander et al. (2012). Solid lines and dashed curves represent data regressions and their 95% confidence intervals, respectively (errors are 2σ).

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864
<figure><img src="image_3.png" /><figcaption>Fig. 1</figcaption></figure>
<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 2</figcaption></figure>

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<figure><img src="image_6.png" /><figcaption>Fig. 3</figcaption></figure>

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<figure><img src="image_7.png" /><figcaption>Fig. 4</figcaption></figure>

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<figure><img src="image_8.png" /><figcaption>Fig. 5</figcaption></figure>

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<figure><img src="image_9.png" /><figcaption>Fig. 6</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>Fig. 7</figcaption></figure>

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<figure><img src="image_11.png" /><figcaption>Fig. 8</figcaption></figure>

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<table><caption>Table 1: Hydrogen abundances and isotopic compositions of chondrites.</caption><thead><tr><th>Meteorite</th><th>Type</th><th>wt% H</th><th>err. (2σ)</th><th>2 sd</th><th>δD (‰)</th><th>err. (2σ)</th><th>2 sd</th><th>D/H (×10<sup>-6</sup>)</th><th>err. (2σ)</th><th>2 sd</th></tr></thead><tbody><tr><td>Aguas Zarcas (n = 2)</td><td>CM2</td><td>0.868</td><td>0.045</td><td>0.087</td><td>-107.1</td><td>2</td><td>1.6</td><td>139.1</td><td>0.3</td><td>0.3</td></tr><tr><td>Jbilet Winselwan (n = 2)</td><td>CM2</td><td>0.471</td><td>0.032</td><td>0.018</td><td>-38.9</td><td>2</td><td>9.5</td><td>149.7</td><td>0.3</td><td>1.5</td></tr><tr><td>LON 94101 (n = 2)<sup>c</sup></td><td>CM2</td><td>0.832</td><td>0.045</td><td>0.012</td><td>-154.6</td><td>2</td><td>3.1</td><td>131.7</td><td>0.3</td><td>0.5</td></tr><tr><td>Maribo (n = 2)</td><td>CM2</td><td>0.794</td><td>0.044</td><td>0.028</td><td>-37.9</td><td>2</td><td>1.1</td><td>149.9</td><td>0.3</td><td>0.2</td></tr><tr><td>Mighei (n = 2)</td><td>CM2</td><td>0.910</td><td>0.047</td><td>0.038</td><td>-109.4</td><td>2</td><td>0.8</td><td>138.7</td><td>0.3</td><td>0.1</td></tr><tr><td>Mukundpura (n = 4)</td><td>CM2</td><td>1.013</td><td>0.048</td><td>0.139</td><td>-158.2</td><td>2</td><td>6.7</td><td>131.1</td><td>0.3</td><td>1</td></tr><tr><td>Murchison (n = 2)</td><td>CM2</td><td>0.828</td><td>0.046</td><td>0.081</td><td>-74.9</td><td>2</td><td>0.9</td><td>144.1</td><td>0.3</td><td>0.1</td></tr><tr><td>Murray (n = 2)</td><td>CM2</td><td>0.842</td><td>0.046</td><td>0.038</td><td>-18.5</td><td>2</td><td>2.6</td><td>152.9</td><td>0.3</td><td>0.4</td></tr><tr><td>Paris (altered area)<sup>a</sup></td><td>CM2</td><td>0.686</td><td>0.040</td><td></td><td>93.7</td><td>2</td><td></td><td>170.4</td><td>0.3</td><td></td></tr><tr><td>Paris<sup>b</sup></td><td>CM2</td><td>0.530</td><td>0.010</td><td></td><td>120.3</td><td>1</td><td></td><td>174.5</td><td>0.3</td><td></td></tr><tr><td>Tagish Lake (n = 3)</td><td>Ung. C</td><td>0.433</td><td>0.031</td><td>0.007</td><td>442.3</td><td>2</td><td>24</td><td>224.7</td><td>0.3</td><td>3.7</td></tr><tr><td>Alais (n = 2)</td><td>CI</td><td>0.963</td><td>0.048</td><td>0.092</td><td>133.7</td><td>2</td><td>28.9</td><td>176.6</td><td>0.3</td><td>4.5</td></tr><tr><td>Orgueil (n = 4)</td><td>CI</td><td>0.930</td><td>0.045</td><td>0.148</td><td>138.0</td><td>2</td><td>15.3</td><td>177.3</td><td>0.3</td><td>2.4</td></tr><tr><td>Y-980115 (n = 3)<sup>d</sup></td><td>CY</td><td>0.710</td><td>0.041</td><td>0.212</td><td>-106.0</td><td>2</td><td>3</td><td>139.2</td><td>0.3</td><td>0.5</td></tr><tr><td>Allende (n = 2)</td><td>CV</td><td>0.068</td><td>0.011</td><td>0.011</td><td>-109.9</td><td>2</td><td>2.4</td><td>138.6</td><td>0.8</td><td>0.4</td></tr><tr><td>Bali</td><td>CV</td><td>0.060</td><td>0.010</td><td></td><td>-9.3</td><td>5</td><td></td><td>154.3</td><td>0.8</td><td></td></tr><tr><td>Grosnaja</td><td>CV</td><td>0.191</td><td>0.019</td><td></td><td>-90.5</td><td>5</td><td></td><td>141.7</td><td>0.8</td><td></td></tr><tr><td>Kaba</td><td>CV</td><td>0.110</td><td>0.014</td><td></td><td>32.6</td><td>5</td><td></td><td>160.8</td><td>0.8</td><td></td></tr><tr><td>Vigarano</td><td>CV</td><td>0.158</td><td>0.018</td><td></td><td>-72.6</td><td>5</td><td></td><td>144.5</td><td>0.8</td><td></td></tr><tr><td>Karoonda</td><td>CK</td><td>0.013</td><td>0.004</td><td></td><td>-107.4</td><td>5</td><td></td><td>139.0</td><td>0.8</td><td></td></tr><tr><td>Bjurbole</td><td>LL/L4</td><td>0.053</td><td>0.009</td><td></td><td>-128.1</td><td>5</td><td></td><td>135.8</td><td>0.8</td><td></td></tr><tr><td>GRO 95502<sup>e</sup></td><td>L3</td><td>0.199</td><td>0.020</td><td></td><td>-73.2</td><td>5</td><td></td><td>144.4</td><td>0.8</td><td></td></tr><tr><td>Saratov (n = 2)</td><td>L4</td><td>0.029</td><td>0.006</td><td>0.011</td><td>-113.7</td><td>5</td><td>2.3</td><td>138.1</td><td>0.8</td><td>0.4</td></tr><tr><td>Sainte Marguerite</td><td>H4</td><td>0.010</td><td>0.004</td><td></td><td>-135.8</td><td>5</td><td></td><td>134.6</td><td>0.8</td><td></td></tr><tr><td>Kernouve</td><td>H6</td><td>0.008</td><td>0.003</td><td></td><td>-138.3</td><td>5</td><td></td><td>134.2</td><td>0.8</td><td></td></tr></tbody></table>

922 <sup>a</sup>Piece of Paris provided by Bekaert et al. (2018). <sup>b</sup>Data from Vacher et al. (2016) using the same methodology as this study. <sup>c</sup>Lonewolf Nunataks 94101. <sup>d</sup>Yamato 980115. <sup>e</sup>Grosvenor Mountains.

923 Err. (2σ): 2σ sample error (see methods). 2 sd: 2σ standard deviation on *n* replicates.

924 Err. (2σ): 2σ sample error (see methods). 2 sd: 2σ standard deviation on *n* replicates.

925
<table><caption>Table 2: Carbon and nitrogen abundances and carbon isotopic compositions of chondrites.</caption><thead><tr><th>Meteorite</th><th>Type</th><th>wt% N</th><th>err.<br>(2σ)</th><th>2 sd</th><th>wt% C</th><th>err.<br>(2σ)</th><th>2 sd</th><th>δ<sup>13</sup>C<br>(‰)</th><th>err.<br>(2σ)</th><th>2 sd</th></tr></thead><tbody><tr><td>Aguas Zarcas</td><td>CM2</td><td>0.098</td><td>0.029</td><td></td><td>2.13</td><td>0.04</td><td></td><td>-9.8</td><td>0.2</td><td></td></tr><tr><td>Jbilet Winselwan</td><td>CM2</td><td>0.095</td><td>0.029</td><td></td><td>1.54</td><td>0.03</td><td></td><td>-10.9</td><td>0.2</td><td></td></tr><tr><td>LON 94101<sup>a</sup></td><td>CM2</td><td>0.102</td><td>0.031</td><td></td><td>1.91</td><td>0.04</td><td></td><td>-13.7</td><td>0.2</td><td></td></tr><tr><td>Maribo</td><td>CM2</td><td>0.114</td><td>0.034</td><td></td><td>2.18</td><td>0.04</td><td></td><td>-5.5</td><td>0.2</td><td></td></tr><tr><td>Mighei</td><td>CM2</td><td>0.103</td><td>0.031</td><td></td><td>2.92</td><td>0.06</td><td></td><td>-12.5</td><td>0.2</td><td></td></tr><tr><td>Mukundpura (n = 3)</td><td>CM2</td><td>0.086</td><td>0.086</td><td>0.008</td><td>2.08</td><td>0.04</td><td>0.04</td><td>-3.9</td><td>0.2</td><td>2.3</td></tr><tr><td>Murchison</td><td>CM2</td><td>0.092</td><td>0.092</td><td></td><td>2.30</td><td>0.05</td><td></td><td>-10.4</td><td>0.2</td><td></td></tr><tr><td>Murray</td><td>CM2</td><td>0.134</td><td>0.040</td><td></td><td>3.04</td><td>0.06</td><td></td><td>-11.7</td><td>0.2</td><td></td></tr><tr><td>Paris</td><td>CM2</td><td>0.172</td><td>0.052</td><td></td><td>2.67</td><td>0.05</td><td></td><td>-7.5</td><td>0.2</td><td></td></tr><tr><td>Tagish Lake</td><td>Ung. C</td><td>0.112</td><td>0.034</td><td></td><td>2.14</td><td>0.04</td><td></td><td>4.7</td><td>0.2</td><td></td></tr><tr><td>Alais</td><td>CI</td><td>0.173</td><td>0.052</td><td></td><td>3.33</td><td>0.07</td><td></td><td>-15.9</td><td>0.2</td><td></td></tr><tr><td>Orgueil (n = 2)</td><td>CI</td><td>0.205</td><td>0.062</td><td>0.014</td><td>3.35</td><td>0.07</td><td>0.78</td><td>-12.9</td><td>0.2</td><td>5.7</td></tr><tr><td>Y-980115<sup>b</sup></td><td>CY</td><td>0.090</td><td>0.090</td><td></td><td>3.06</td><td>0.06</td><td></td><td>-12.9</td><td>0.2</td><td></td></tr><tr><td>Allende</td><td>CV</td><td>0.012</td><td>0.012</td><td></td><td>0.55</td><td>0.01</td><td></td><td>-23.7</td><td>0.2</td><td></td></tr><tr><td>Bali</td><td>CV</td><td>bdl</td><td></td><td></td><td>0.85</td><td>0.02</td><td></td><td>-19.9</td><td>0.2</td><td></td></tr><tr><td>Grosnaja</td><td>CV</td><td>0.034</td><td>0.034</td><td></td><td>0.51</td><td>0.01</td><td></td><td>-21.6</td><td>0.2</td><td></td></tr><tr><td>Kaba</td><td>CV</td><td>0.030</td><td>0.030</td><td></td><td>1.42</td><td>0.03</td><td></td><td>-17.8</td><td>0.2</td><td></td></tr><tr><td>Vigarano</td><td>CV</td><td>bdl</td><td></td><td></td><td>bdl</td><td></td><td></td><td>bdl</td><td>0.2</td><td></td></tr><tr><td>Karoonda</td><td>CK</td><td>bdl</td><td></td><td></td><td>0.09</td><td>0.00</td><td></td><td>-20.7</td><td>0.2</td><td></td></tr><tr><td>Bjurbole</td><td>LL/L4</td><td>bdl</td><td></td><td></td><td>0.14</td><td>0.00</td><td></td><td>-26.5</td><td>0.2</td><td></td></tr><tr><td>GRO 95502<sup>c</sup></td><td>L3</td><td>bdl</td><td></td><td></td><td>bdl</td><td></td><td></td><td>bdl</td><td>0.2</td><td></td></tr><tr><td>Saratov</td><td>L4</td><td>bdl</td><td></td><td></td><td>0.12</td><td>0.00</td><td></td><td>-26.2</td><td>0.2</td><td></td></tr><tr><td>Sainte Marguerite</td><td>H4</td><td>bdl</td><td></td><td></td><td>0.08</td><td>0.00</td><td></td><td>-24.7</td><td>0.2</td><td></td></tr><tr><td>Kernouve</td><td>H6</td><td>bdl</td><td></td><td></td><td>0.10</td><td>0.00</td><td></td><td>-26.6</td><td>0.2</td><td></td></tr></tbody></table>

<sup>a</sup>Lonewolf Nunataks 94101, <sup>b</sup>Yamato 980115 <sup>c</sup>Grosvenor Mountains.

Err. (2σ): 2σ sample error (see methods), 2 sd: 2σ standard deviation on *n* replicates.

926

927

928

929

930

931

932

933

934

935

936

937

938