High temperature noble gas thermometry in Lake Kivu, East Africa.

Due to their biological and chemical inertness, noble gases in natural waters are widely used to trace natural waters and to determine ambient temperature conditions during the last intensive contact with the atmosphere (equilibration). Noble gas solubilities are strong functions of temperature, with higher temperatures resulting in lower concentrations. Thus far, only common environmental conditions have been considered, and hence investigated temperatures have almost never exceeded 35 °C, but environmental scenarios that generate higher surface-water temperatures (such as volcanism) exist nonetheless. Recently published measurements of noble gas concentrations in Lake Kivu, which sits at the base of the Nyiragongo volcano in East Africa, unexpectedly show that the deep waters are strongly depleted in noble gases with respect to in-situ conditions, and so far no quantitative explanation for this observation has been provided. We make use of recently published noble gas solubility data at higher temperatures to investigate our hypothesis that unusually high equilibration temperatures could have caused the low measured noble gas concentrations by applying various approaches of noble gas thermometry. Noble gas concentration ratios and least squares fitting of individual concentrations indicate that the data agrees best with the assumption that deep water originates from groundwater formed at temperatures of about 65 °C. Thus, no form of degassing is required to explain the observed noble gas depletion: the deep water currently contained in Lake Kivu has most probably never experienced a large scale degassing event. This conclusion is important as limnic eruptions were feared to threaten the lives of the local population.

Widespread six degrees Celsius cooling on land during the Last Glacial Maximum.

The magnitude of global cooling during the Last Glacial Maximum (LGM, the coldest multimillennial interval of the last glacial period) is an important constraint for evaluating estimates of Earth's climate sensitivity1,2. Reliable LGM temperatures come from high-latitude ice cores3,4, but substantial disagreement exists between proxy records in the low latitudes1,5-8, where quantitative low-elevation records on land are scarce. Filling this data gap, noble gases in ancient groundwater record past land surface temperatures through a direct physical relationship that is rooted in their temperature-dependent solubility in water9,10. Dissolved noble gases are suitable tracers of LGM temperature because of their complete insensitivity to biological and chemical processes and the ubiquity of LGM-aged groundwater around the globe11,12. However, although several individual noble gas studies have found substantial tropical LGM cooling13-16, they have used different methodologies and provide limited spatial coverage. Here we use noble gases in groundwater to show that the low-altitude, low-to-mid-latitude land surface (45 degrees south to 35 degrees north) cooled by 5.8 ± 0.6 degrees Celsius (mean ± 95% confidence interval) during the LGM. Our analysis includes four decades of groundwater noble gas data from six continents, along with new records from the tropics, all of which were interpreted using the same physical framework. Our land-based result broadly supports a recent reconstruction based on marine proxy data assimilation1 that suggested greater climate sensitivity than previous estimates5-7.

Estimating Inert Gas Bubbling from Simple SCUBA Diving Parameters.

Inert gas bubbles frequently occur in SCUBA divers' vascular systems, eventually leading to decompression accidents. Only in professional settings, dive profiles can be adjusted on individual basis depending on bubble grades detected through ultrasonography. A total of 342 open-circuit air dives following sports diving profiles were assessed using echocardiography. Subsequently, (Eftedal-Brubakk) bubble grades were correlated with dive and individual parameters. Post-dive cardiac bubbles were observed in 47% of all dives and bubble grades were significantly correlated with depth (r=0.46), air consumption (r=0.41), age (r=0.25), dive time (r=0.23), decompression diving (r=0.19), surface time (r=- 0.12). Eftedal-Brubakk categorical bubble grades for sports diving with compressed air can be approximated by bubble grade = (age*50-1 - surface time*150-1+maximum depth*45-1+air consumption*4500-1)2 (units in years, hours, meter, and bar*liter; R2=0.31). Thus, simple dive and individual parameters allow reasonable estimation of especially relevant medium to higher bubble grades for information on relevant decompression stress after ascent. Echo bubble grade 0 is overestimated by the formula derived. However, echo might fail to detect minor bubbling only. The categorical prediction of individual decompression stress with simple bio and dive data should be evaluated further to be developed towards dive computer included automatic ex-post information for decision-making on individual safety measures.

Theoretical Prediction on the New Types of Noble Gas Containing Anions OBONgO- and OCNNgO- (Ng = He, Ar, Kr and Xe).

The fluorine-less noble gas containing anions OBONgO- and OCNNgO- have been studied by correlated electronic structure calculation and density functional theory. The obtained energetics indicates that for Ng = Kr and Xe, these anions should be kinetically stable at low temperature. The molecular structures and electron density distribution suggests that these anions are stabilized by ion-induced dipole interactions with charges concentrated on the electronegative OBO and OCN groups. The current study shows that in addition to the fluoride ion, polyatomic groups with strong electronic affinities can also form stable noble gas containing anions of the type Y-…NgO.

Noble-Gas Chemistry More than Half a Century after the First Report of the Noble-Gas Compound.

Recent development in the synthesis and characterization of noble-gas compounds is reviewed, i.e., noble-gas chemistry reported in the last five years with emphasis on the publications issued after 2017. XeF2 is commercially available and has a wider practical application both in the laboratory use and in the industry. As a ligand it can coordinate to metal centers resulting in [M(XeF2)x]n+ salts. With strong Lewis acids, XeF2 acts as a fluoride ion donor forming [XeF]+ or [Xe2F3]+ salts. Latest examples are [Xe2F3][RuF6]·XeF2, [Xe2F3][RuF6] and [Xe2F3][IrF6]. Adducts NgF2·CrOF4 and NgF2·2CrOF4 (Ng = Xe, Kr) were synthesized and structurally characterized at low temperatures. The geometry of XeF6 was studied in solid argon and neon matrices. Xenon hexafluoride is a well-known fluoride ion donor forming various [XeF5]+ and [Xe2F11]+ salts. A large number of crystal structures of previously known or new [XeF5]+ and [Xe2F11]+ salts were reported, i.e., [Xe2F11][SbF6], [XeF5][SbF6], [XeF5][Sb2F11], [XeF5][BF4], [XeF5][TiF5], [XeF5]5[Ti10F45], [XeF5][Ti3F13], [XeF5]2[MnF6], [XeF5][MnF5], [XeF5]4[Mn8F36], [Xe2F11]2[SnF6], [Xe2F11]2[PbF6], [XeF5]4[Sn5F24], [XeF5][Xe2F11][CrVOF5]·2CrVIOF4, [XeF5]2[CrIVF6]·2CrVIOF4, [Xe2F11]2[CrIVF6], [XeF5]2[CrV2O2F8], [XeF5]2[CrV2O2F8]·2HF, [XeF5]2[CrV2O2F8]·2XeOF4, A[XeF5][SbF6]2 (A = Rb, Cs), Cs[XeF5][BixSb1-xF6]2 (x = ~0.37-0.39), NO2XeF5(SbF6)2, XeF5M(SbF6)3 (M = Ni, Mg, Zn, Co, Cu, Mn and Pd) and (XeF5)3[Hg(HF)]2(SbF6)7. Despite its extreme sensitivity, many new XeO3 adducts were synthesized, i.e., the 15-crown adduct of XeO3, adducts of XeO3 with triphenylphosphine oxide, dimethylsulfoxide and pyridine-N-oxide, and adducts between XeO3 and N-bases (pyridine and 4-dimethylaminopyridine). [Hg(KrF2)8][AsF6]2·2HF is a new example of a compound in which KrF2 serves as a ligand. Numerous new charged species of noble gases were reported (ArCH2+, ArOH+, [ArB3O4]+, [ArB3O5]+, [ArB4O6]+, [ArB5O7]+, [B12(CN)11Ne]-). Molecular ion HeH+ was finally detected in interstellar space. The discoveries of Na2He and ArNi at high pressure were reported. Bonding motifs in noble-gas compounds are briefly commented on in the last paragraph of this review.

Migration of noble gas tracers at the site of an underground nuclear explosion at the Nevada National Security Site.

As part of an underground gas migration study, two radioactive noble gases (37Ar and 127Xe) and two stable tracer gases (SF6 and PFDMCH) were injected into a historic nuclear explosion test chimney and allowed to migrate naturally. The purpose of this experiment was to provide a bounding case (natural transport) for the flow of radioactive noble gases following an underground nuclear explosion. To accomplish this, soil gas samples were collected from a series of boreholes and a range of depths from the shallow subsurface (3 m) to deeper levels (~160 m) over a period of eleven months. These samples have provided insights into the development and evolution of the subsurface plume and constrained the relative migration rates of the radioactive and stable gas species in the case when the driving pressure from the cavity is low. Analysis of the samples concluded that the stable tracer SF6 was consistently enriched in the subsurface samples relative to the radiotracer 127Xe, but the ratios of SF6 and 37Ar remained similar throughout the samples.

Measuring lung function in airways diseases: current and emerging techniques.

Chronic airways diseases, including asthma, COPD and cystic fibrosis, cause significant morbidity and mortality and are associated with high healthcare expenditure, in the UK and worldwide. For patients with these conditions, improvements in clinical outcomes are likely to depend on the application of precision medicine, that is, the matching of the right treatment to the right patient at the right time. In this context, the identification and targeting of 'treatable traits' is an important priority in airways disease, both to ensure the appropriate use of existing treatments and to facilitate the development of new disease-modifying therapy. This requires not only better understanding of airway pathophysiology but also an enhanced ability to make physiological measurements of disease activity and lung function and, if we are to impact on the natural history of these diseases, reliable measures in early disease. In this article, we outline some of the key challenges faced by the respiratory community in the management of airways diseases, including early diagnosis, disease stratification and monitoring of therapeutic response. In this context, we review the advantages and limitations of routine physiological measurements of respiratory function including spirometry, body plethysmography and diffusing capacity and discuss less widely used methods such as forced oscillometry, inert gas washout and the multiple inert gas elimination technique. Finally, we highlight emerging technologies including imaging methods such as quantitative CT and hyperpolarised gas MRI as well as quantification of lung inhomogeneity using precise in-airway gas analysis and mathematical modelling. These emerging techniques have the potential to enhance existing measures in the assessment of airways diseases, may be particularly valuable in early disease, and should facilitate the efforts to deliver precision respiratory medicine.

The characteristic release of noble gases from an underground nuclear explosion.

Prompt release of gases at the ground surface resulting from explosively propagated vents or large operational releases has typically been considered to be the only mode of transport for detonation gases from an underground nuclear explosion (UNE) giving rise to detectable levels of radioxenon gases in downwind atmospheric samples captured at distances exceeding 100 km. Using a model for thermally and barometrically driven post-detonation transport across the broad surface of a simulated UNE site, we show in conjunction with the results of an atmospheric tracer-release experiment that even deep, well-contained UNEs, without prompt vents or leaks, are potentially detectable tens of kilometers downwind with current technology; distances that are significant for localizing the source of detected atmospheric signals during on-site monitoring or inspection. For a given yield, the bulk permeability of the UNE site and to a lesser extent the depth of detonation appear to be the primary source-term parameters controlling the distance of detection from the detonation point. We find for test-site bulk permeabilities exceeding 1 darcy (10-12 m2) that broad-area surface fluxes of radioxenon gas exhibit exponential dependence on permeability resulting in order-of-magnitude enhancements of surface flux for changes in permeability of only a darcy. Simulations of subsurface transport assuming a canonical detonation-depth-versus-nuclear-yield relationship generally resulted in larger atmospheric signals for shallower, lower-yield explosions allowing downwind detection at distances greater than 1000 km. Additionally, atmospheric simulations suggest that the lowest atmospheric boundary layer heights, such as occur at night, produced concentrations above minimum detectable levels at the greatest distances downwind.

Archean kerogen as a new tracer of atmospheric evolution: Implications for dating the widespread nature of early life.

Understanding the composition of the Archean atmosphere is vital for unraveling the origin of volatiles and the environmental conditions that led to the development of life. The isotopic composition of xenon in the Archean atmosphere has evolved through time by mass-dependent fractionation from a precursor comprising cometary and solar/chondritic contributions (referred to as U-Xe). Evaluating the composition of the Archean atmosphere is challenging because limited amounts of atmospheric gas are trapped within minerals during their formation. We show that organic matter, known to be efficient at preserving large quantities of noble gases, can be used as a new archive of atmospheric noble gases. Xe isotopes in a kerogen isolated from the 3.0-billion-year-old Farrel Quartzite (Pilbara Craton, Western Australia) are mass fractionated by 9.8 ± 2.1 per mil (‰) (2σ) per atomic mass unit, in line with a progressive evolution toward modern atmospheric values. Archean atmospheric Xe signatures in kerogens open a new avenue for following the evolution of atmospheric composition through time. The degree of mass fractionation of Xe isotopes relative to the modern atmosphere can provide a time stamp for dating Archean kerogens and therefore narrowing the time window for the diversification of early life during the Archean eon.

Mean global ocean temperatures during the last glacial transition.

Little is known about the ocean temperature's long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 ± 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO2, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.

Geostatistical analysis of tritium, groundwater age and other noble gas derived parameters in California.

Key characteristics of California groundwater systems related to aquifer vulnerability, sustainability, recharge locations and mechanisms, and anthropogenic impact on recharge are revealed in a spatial geostatistical analysis of a unique data set of tritium, noble gases and other isotopic analyses unprecedented in size at nearly 4000 samples. The correlation length of key groundwater residence time parameters varies between tens of kilometers ((3)H; age) to the order of a hundred kilometers ((4)Heter; (14)C; (3)Hetrit). The correlation length of parameters related to climate, topography and atmospheric processes is on the order of several hundred kilometers (recharge temperature; δ(18)O). Young groundwater ages that highlight regional recharge areas are located in the eastern San Joaquin Valley, in the southern Santa Clara Valley Basin, in the upper LA basin and along unlined canals carrying Colorado River water, showing that much of the recent recharge in central and southern California is dominated by river recharge and managed aquifer recharge. Modern groundwater is found in wells with the top open intervals below 60 m depth in the southeastern San Joaquin Valley, Santa Clara Valley and Los Angeles basin, as the result of intensive pumping and/or managed aquifer recharge operations.

A method for estimating (41)Ar, (85)(,88)Kr and (131m,133)Xe doses to non-human biota.

A method is presented for estimating (41)Ar, (85,88)Kr and (131m,133)Xe dose rates to terrestrial wildlife without having to resort to comparisons with analogue radionuclides. The approach can be used to calculate the dose rates arising from external exposures to given ambient air concentrations of these isotopes. Dose conversion coefficient (DCC) values for a range of representative organisms are calculated, using a Monte Carlo approach to generate absorbed fractions based on representing animals as reference ellipsoid geometries. Plume immersion is the main component of the total DCC. DCC values calculated for a human-sized organism are compared with human dose conversion factors from ICRP Publication 119, demonstrating the consistency of the biota approach with that for humans. An example of application is provided for hypothetical nuclear power plant atmospheric discharges with associated exposures to birds and insects. In this example, the dose rates appear to be dominated by (133)Xe and (88)Kr, respectively. The biota considered would be protected from the effects of noble gas radiation from a population protection perspective.

Stream measurements locate thermogenic methane fluxes in groundwater discharge in an area of shale-gas development.

The environmental impacts of shale-gas development on water resources, including methane migration to shallow groundwater, have been difficult to assess. Monitoring around gas wells is generally limited to domestic water-supply wells, which often are not situated along predominant groundwater flow paths. A new concept is tested here: combining stream hydrocarbon and noble-gas measurements with reach mass-balance modeling to estimate thermogenic methane concentrations and fluxes in groundwater discharging to streams and to constrain methane sources. In the Marcellus Formation shale-gas play of northern Pennsylvania (U.S.A.), we sampled methane in 15 streams as a reconnaissance tool to locate methane-laden groundwater discharge: concentrations up to 69 µg L(-1) were observed, with four streams ≥ 5 µg L(-1). Geochemical analyses of water from one stream with high methane (Sugar Run, Lycoming County) were consistent with Middle Devonian gases. After sampling was completed, we learned of a state regulator investigation of stray-gas migration from a nearby Marcellus Formation gas well. Modeling indicates a groundwater thermogenic methane flux of about 0.5 kg d(-1) discharging into Sugar Run, possibly from this fugitive gas source. Since flow paths often coalesce into gaining streams, stream methane monitoring provides the first watershed-scale method to assess groundwater contamination from shale-gas development.

Noble gases identify the mechanisms of fugitive gas contamination in drinking-water wells overlying the Marcellus and Barnett Shales.

Horizontal drilling and hydraulic fracturing have enhanced energy production but raised concerns about drinking-water contamination and other environmental impacts. Identifying the sources and mechanisms of contamination can help improve the environmental and economic sustainability of shale-gas extraction. We analyzed 113 and 20 samples from drinking-water wells overlying the Marcellus and Barnett Shales, respectively, examining hydrocarbon abundance and isotopic compositions (e.g., C2H6/CH4, δ(13)C-CH4) and providing, to our knowledge, the first comprehensive analyses of noble gases and their isotopes (e.g., (4)He, (20)Ne, (36)Ar) in groundwater near shale-gas wells. We addressed two questions. (i) Are elevated levels of hydrocarbon gases in drinking-water aquifers near gas wells natural or anthropogenic? (ii) If fugitive gas contamination exists, what mechanisms cause it? Against a backdrop of naturally occurring salt- and gas-rich groundwater, we identified eight discrete clusters of fugitive gas contamination, seven in Pennsylvania and one in Texas that showed increased contamination through time. Where fugitive gas contamination occurred, the relative proportions of thermogenic hydrocarbon gas (e.g., CH4, (4)He) were significantly higher (P < 0.01) and the proportions of atmospheric gases (air-saturated water; e.g., N2, (36)Ar) were significantly lower (P < 0.01) relative to background groundwater. Noble gas isotope and hydrocarbon data link four contamination clusters to gas leakage from intermediate-depth strata through failures of annulus cement, three to target production gases that seem to implicate faulty production casings, and one to an underground gas well failure. Noble gas data appear to rule out gas contamination by upward migration from depth through overlying geological strata triggered by horizontal drilling or hydraulic fracturing.

Conquering the outdoors with on-site mass spectrometry.

In recent years, mass spectrometers with a membrane inlet separating gases from water for final analysis have been used successfully for the on-site quantification of dissolved gases in surface waters. In 'classical' membrane inlet mass spectrometers (MIMS), the membrane directly separates the water from the high-vacuum environment of the mass spectrometer. The gas equilibrium MIMS (GE-MIMS) that is described in this review, however, makes use of an intermediate pressure reduction stage after the membrane inlet. Hence, the gas concentrations after the membrane are at steady state, near solubility equilibrium with the water to be analyzed. This setup has several advantages over classical MIMS, which enable autonomous and continuous in-field operation. The GE-MIMS can be used to acquire noble gas concentration time series (NGTS). Noble gases are useful tracers for physical gas exchange and transport in groundwater and other aqueous systems. Hence NGTS enable the temporal dynamics of physical gas exchange and transport in groundwater and other aqueous systems to be investigated. To determine the O2 turnover that has occurred in groundwater since recharge, both the O2 concentration in situ and the total input of O2 to the groundwater since recharge is needed. Determination of the latter is only possible if the relevant physical exchange and transport mechanisms can be quantified. In particular, gas exchange between soil air and groundwater often significantly affects groundwater O2 concentrations. Determination of O2 turnover in groundwater therefore requires a combined analysis of O2 and noble gas concentrations.

Electron paramagnetic resonance measurements of absorbed dose in teeth from citizens of Ozyorsk.

In 1945, within the frame of the Uranium Project for the production of nuclear weapons, the Mayak nuclear facilities were constructed at the Lake Irtyash in the Southern Urals, Russia. The nuclear workers of the Mayak Production Association (MPA), who lived in the city of Ozyorsk, are the focus of epidemiological studies for the assessment of health risks due to protracted exposure to ionising radiation. Electron paramagnetic resonance measurements of absorbed dose in tooth enamel have already been used in the past, in an effort to validate occupational external doses that were evaluated in the Mayak Worker Dosimetry System. In the present study, 229 teeth of Ozyorsk citizens not employed at MPA were investigated for the assessment of external background exposure in Ozyorsk. The annually absorbed dose in tooth enamel from natural background radiation was estimated to be (0.7 ± 0.3) mGy. For citizens living in Ozyorsk during the time of routine noble gas releases of the MPA, which peaked in 1953, the average excess absorbed dose in enamel above natural background was (36 ± 29) mGy, which is consistent with the gamma dose obtained by model calculations. In addition, there were indications of possible accidental gaseous MPA releases that affected the population of Ozyorsk, during the early and late MPA operation periods, before 1951 and after 1960.

In situ radiometric and exposure age dating of the martian surface.

We determined radiogenic and cosmogenic noble gases in a mudstone on the floor of Gale Crater. A K-Ar age of 4.21 ± 0.35 billion years represents a mixture of detrital and authigenic components and confirms the expected antiquity of rocks comprising the crater rim. Cosmic-ray-produced (3)He, (21)Ne, and (36)Ar yield concordant surface exposure ages of 78 ± 30 million years. Surface exposure occurred mainly in the present geomorphic setting rather than during primary erosion and transport. Our observations are consistent with mudstone deposition shortly after the Gale impact or possibly in a later event of rapid erosion and deposition. The mudstone remained buried until recent exposure by wind-driven scarp retreat. Sedimentary rocks exposed by this mechanism may thus offer the best potential for organic biomarker preservation against destruction by cosmic radiation.

On the abundances of noble and biologically relevant gases in Lake Vostok, Antarctica.

Motivated by the possibility of comparing theoretical predictions of Lake Vostok's composition with future in situ measurements, we investigated the composition of clathrates that are expected to form in this environment from the air supplied to the lake by melting ice. To establish the best possible correlation between the lake water composition and that of air clathrates formed in situ, we used a statistical thermodynamic model based on the description of the guest-clathrate interaction by a spherically averaged Kihara potential with a nominal set of potential parameters. We determined the fugacities of the different volatiles present in the lake by defining a "pseudo" pure substance dissolved in water owning the average properties of the mixture and by using the Redlich-Kwong equation of state to mimic its thermodynamic behavior. Irrespective of the clathrate structure considered in our model, we found that xenon and krypton are strongly impoverished in the lake water (a ratio in the 0.04-0.1 range for xenon and a ratio in the ≈ 0.15-0.3 range for krypton) compared to their atmospheric abundances. Argon and methane were also found to be depleted in the Lake Vostok water by factors in the 0.5-0.95 and 0.3-0.5 ranges, respectively, compared to their atmospheric abundances. On the other hand, the carbon dioxide abundance was found to be substantially enriched in the lake water compared to its atmospheric abundance (by a factor in the 1.6-5 range at 200 residence times). The comparison of our predictions of the CO2 and CH4 mole fractions in Lake Vostok with future in situ measurements will allow disentangling between the possible supply sources.

Deep fracture fluids isolated in the crust since the Precambrian era.

Fluids trapped as inclusions within minerals can be billions of years old and preserve a record of the fluid chemistry and environment at the time of mineralization. Aqueous fluids that have had a similar residence time at mineral interfaces and in fractures (fracture fluids) have not been previously identified. Expulsion of fracture fluids from basement systems with low connectivity occurs through deformation and fracturing of the brittle crust. The fractal nature of this process must, at some scale, preserve pockets of interconnected fluid from the earliest crustal history. In one such system, 2.8 kilometres below the surface in a South African gold mine, extant chemoautotrophic microbes have been identified in fluids isolated from the photosphere on timescales of tens of millions of years. Deep fracture fluids with similar chemistry have been found in a mine in the Timmins, Ontario, area of the Canadian Precambrian Shield. Here we show that excesses of (124)Xe, (126)Xe and (128)Xe in the Timmins mine fluids can be linked to xenon isotope changes in the ancient atmosphere and used to calculate a minimum mean residence time for this fluid of about 1.5 billion years. Further evidence of an ancient fluid system is found in (129)Xe excesses that, owing to the absence of any identifiable mantle input, are probably sourced in sediments and extracted by fluid migration processes operating during or shortly after mineralization at around 2.64 billion years ago. We also provide closed-system radiogenic noble-gas ((4)He, (21)Ne, (40)Ar, (136)Xe) residence times. Together, the different noble gases show that ancient pockets of water can survive the crustal fracturing process and remain in the crust for billions of years.