Marine Trematosaurid Temnospondyls from the Early Triassic of Western Australia.

The Temnospondyls were an ancient group of Tetrapods, which are the sister group to the modern Lisamphibians (Frogs, Salamanders, and Caecilians), although they were in many ways more Reptile-like, with many apparently able to live completely away from water for much of their lives, while others colonised marine environments. The first Temnospondyls appeared in the Carboniferous, rapidly expanding to become one of the most diverse and abundant groups of terrestrial Vertebrates. The Temnospondyls remained a major group throughout the Permian and Triassic, but were badly affected by the End Triassic extinction from which they never recovered. A few Temnospondyl lineages persisted through the Jurassic and into the Early Cretaceous, when they finally disappeared.

The Trematosaurids were a group of Temnospondyls which migrated into marine environments in the Early Triassic, evolving to occupy a large marine predator role which had become vacant during the End Permian Extinction, and spreading throughout much of the world's environments. Trematosaurids have been described from Madagascar, Greenland, Australia, Pakistan, Spitsbergen, European Russia, the Russian Far East, Germany, and Jordan. 

To date, only a single species of Marine Trematosaurid (several others are known from clearly non-marine environments) has been described from Australia, Erythrobatrachus noonkanbahensis, which described in 1972 by John Cosgriff and Neil Garbutt on the basis of a composite of fragmentary cranial remains from the Early Triassic Blina Shale of the central-southern Kimberley region of far northwestern Western Australia, collected during a series of expeditions to the area in the 1960s.

The Blina Shale records a transgressive delta setting (setting where the land is extending into the sea over a delta system), which would have faced onto the East Gondwana interior rift seaway. These deposits record a mixture of saline, brackish, and freshwater environments, and have produced non-Trematosaurid Temnospondyls such as the Rhytidosteid, Deltasaurus kimberleyensis, the Capitosauroid, Warrenisuchus aliciae, and the Brachyopids, Batrachosuchus henwoodi, and Banksiops townrowi. A variety of other fossils have also been found within the Blida Shale, including the ubiquitous Triassic Saurichthyid Actinopterygian, Saurichthys, a variety of Ceolacanths, the Ptychoceratodontid Lungfish, Ptychoceratodus philippsi, the Sagenodontid Lungfish, Aphelodus anapes, the Ceratodontid Lungfish, Asiatoceratodus tiguidensis, several possible Sharks, Conodonts, Insects, Spinicaudatans and Lingulid Brachiopods, possible Pseudomonotid Bivalves, indeterminate Ammonoids, some possible Mollusc egg cases, burrow traces, palynomorphs (fossil pollen and spores), Achritarchs, Horsetails, and possible Lycopods. 

Temnospondyls from the Blina Shale are typically found in a disarticulated state, either as individual bones or accumulations, and show signs of having been transported before their final deposition, including weathering and sorting by size. This is consistent with deposition in beds with preserved ripple marks and thin cross-lamination, which is suggestive of a shallow, tidal environment. 

In a paper published in the Journal of Vertebrate Palaeontology on 22 February 2026, Benjamin Kear of the Department of Palaeobiology at the Swedish Museum of Natural History, Nicolás Campione of the Palaeoscience Research Centre at the University of New England, Mikael Siversson of the Western Australian Museum, and the School of Molecular and Life Sciences at Curtin University, Mohamad Bazzi of the Department of Earth and Planetary Sciences at Stanford University, and Lachlan Hart of the School of Education and Earth and Sustainability Science Research Centre at the University of New South Wales, as well as the Australian Museum Research Institute, reassess that material assigned to Erythrobatrachus noonkanbahensis from the Blinda Shale deposits, and draw new conclusions about the presents of Trematosaurid Temnospondyls in the Early Triassic of Western Australia.

The original material assigned to Erythrobatrachus noonkanbahensis included the holotype, WAM 62.1.46, two topotype specimens, WAM 71.6.22 and WAM 62.1.50, and a high-definition plaster caste of the holotype, WAM 62.1.59 (in taxonomy, a holotype is the specimen from which a species is described, any other specimen considered to belong to the same species as the holotype therefore belongs to that described species, but if the holotype is found to belong to the same species as the previously described holotype of another species, then the newer species is considered invalid; a topotype is a specimen asigned to a species which comes from the same location as the holotype). All of these specimens were placed in the collection of the Western Australian Museum, but when Kear et al. came to look for them, only WAM 62.1.50 and WAM 62.1.59 could be found, WAM 62.1.46 and WAM 71.6.22 having apparently been loaned to John Cosgriff in 1984, at which time he was working at Wayne State University in Detroit, Michigan. 

A search of the palaeontological collection of Wayne State University could not locate these specimens, although WAM 62.1.46 was subsequently found in a search for potentially related specimens in the collection of the University of California Museum of Paleontology, where it had been identified as cf. Tertrema sp., and given the identifier UCMP 65858. The collection of the University of California Museum of Paleontology was also found to contain a second high-definition plaster caste of this specimen, listed as UCMP 65850. The University of California Museum of Paleontology has subsequenty returned WAM 62.1.46 to the Western Australian Museum. 

Also found within the collection of the University of California Museum of Paleontology was a box labelled WAM 62.1.50, however, this was found to be empty, having been 'withdrawn for study' by John Cosgriff in August 1968.

Source locality for the Erythrobatrachus noonkanbahensis holotype (WAM 62.1.46) and referred material (WAM 62.1.50). Map of the Noonkanbah Station area with the Great Northern Highway (1) extending southeast of Derby towards Fitzroy Crossing in northwestern Western Australia. Outcrop areas of the Lower Triassic Blina Shale are shown with the overlying Erskine Sandstone, and Middle Triassic Munkayarra Shale. Kear et al. (2026).

Specimen WAM 62.1.46, the holotype of Erythrobatrachus noonkanbahensis is a steinkern internal cast from the naso-frontal region of the skull and vomero-palatine section of the palate. This, along with the plaster casts WAM 62.1.59 and UCMP 65850, show Erythrobatrachus noonkanbahensis to have had an elongate skull with a basally constricted rostrum, dorsolaterally facing orbits that are positioned close to the lateral jaw margin, broad nasals that contact the lacrimals posterolaterally, and possibly the septo-maxilla near the external bony nasal opening, anteriorly narrow interpterygoid vacuities that are bordered by transversely broad palatines, ctopterygoids apparently lacking large palatal tusks, at least at the ectopterygoid-palatine suture, and a narrow cultriform process of the parasphenoid that divides the interpterygoid vacuities along the palatal midline, and extends to a point level with the anterior edges of the choanae.

High-definition plaster cast (WAM 62.1.59) and holotype specimen (WAM 62.1.46/UCMP 69858) of Erythrobatrachus noonkanbahensis from the Blina Shale. (A) Cast, and (B) original internal steinkern of the naso-frontal section of the cranium in dorsal aspect. (C) Interpretation of the cranial sutures (solid/dashed lines), openings (black fills), and broken/plaster surfaces (hatching). (D) Skull reconstruction in dorsal aspect. (E) Cast and (F) original internal steinkern of the vomero-palatine section of the cranium in ventral aspect. (G) interpretation of the cranial sutures and openings. (H) Skull reconstruction in ventral aspect. Skull outlines based on Tertrema acuta and Hyperokynodon keuperinus. Abbreviations: ch, choana; cp, cultriform process of the parasphenoid; ec, ectopterygoid; fr, frontal; ju, jugal; la, lacrimal; mx, maxilla; na, nasal; nc, nerve channel cast; or, orbit; pf, postfrontal; pl, palatine; pr, prefrontal; pv, pterygoid vacuity; sm, septomaxilla; ?tb, possible palatal tusk base; vo, vomer. Scale bars equal 50 mm. Kear et al. (2026).

Specimen WAM 62.1.50 is an external impression of the vomerine palate showing multiple dental rows and anterior margins of the choanae. This is recorded as a paratype of Erythrobatrachus noonkanbahensis on its Western Australia Museum label (a paratype is a specimen other than the holotype of a species which is used in the formal description of that species), but as 'cf. Aphaneramma' (refer to Aphaneramma) on the label of the empty box at the University of California Museum of Paleontology, a label which Kear et al. assume reflects Cosgriff's original thoughts on the classification of the specimen. Aphaneramma is a cosmopolitan Trematosaurid Temnospondyl also known from the Early Triassic of Pakistan, Madagascar, Russia, and Svarlbard. 

WAM 62.1.50 appears to be similar in proportions to the skull of Aphaneramma gavialimimus, a large (skull-lenght about 400 mm) species of Aphaneramma described from Madagascar in 2017. It also has fine longitudinal bone ridges, which have previously been observed in members of the genera Aphaneramma, Wantzosaurus, and Cosgriffius. The choanae of WAM 62.1.50 are longitudinally offset, such that the left opening would have been displaced anteriorly relative to the right, something which has also been recorded in other specimens of Aphaneramma. In their 1972 description of Erythrobatrachus noonkanbahensis, Cosgriff and Garbutt identify this as being the result of displacement of the right choanae, which they believe was 'compressed and pushed forward from its original position', but which Kear et al. consider may be a diagnostic feature of the genus. Notably, WAM 62.1.50 shows several rows of vomerine teeth (teeth on the roof of the mouth), which are absent in WAM 62.1.46, suggesting the two do not belong to the same species. Vonerine teeth are found in Aphaneramma, as well as some other genera of Trematosaurid Temnospondyls, although the size and arrangement of those of WAM 62.1.50 do not appear to exactly match any previously described taxa. For this reason, Kear et al. return WAM 62.1.50 to the designation cf. Aphaneramma. 

Referred material (WAM 62.1.50) of cf Aphaneramma sp. from the Blina Shale. (A) Palate impression in ventral aspect (coated with ammonium chloride sublimate). (B) Interpretation of the palatal sutures, dentition (solid/dashed lines), and openings (black fills). Skull outline based on Aphaneramma gavialimimus. (C) Skull reconstruction in ventral aspect. Skull outline based on Aphaneramma gavialimimus. Abbreviations: ch, choana; mx, maxilla; tr, tooth row; vo, vomer. Scale bar equals 30 mm in (A) and (B); and 50 mm in (C). Kear et al. (2026).

Cosgriff and Garbutt apparently viewed the additional specimens assigned to Erythrobatrachus noonkanbahensis, WAM 71.6.22 and WAM 62.1.50, as developmental stages of the species, noting that they were smaller than the holotype, WAM 62.1.46. As WAM 71.6.22 could not be located, this assessment could not be evaluated for this specimen, but Kear et al.'s study clearly shows that the smaller size of WAM 62.1.50 only relates to its fragmentary nature, and that it was clearly derived from quite a large animal. Furthermore, it differs significantly in morphology to WAM 62.1.46, and cannot be assigned to the same species.

This expands the diversity of Temnospondyls known from the Blina Shale, and expands our knowledge of how that assemblage relates to wider Temnospondyl faunal distributions in the Early Triassic. This includes widespread Australian species such as Deltasaurus kimberleyensis, Warrenisuchus aliciae, and Banksiops townrowi, taxa also known from South Africa, such as the genus Batrachosuchus, species not found anywhere else, such as Erythrobatrachus noonkanbahensis, and now an example of the globally distributed genus Aphaneramma. This also increases the distribution of these marine Temnospondyls, raising the possibility that their distribution was not just due to expansion along the continuous coastal Tethyan periphery of the Pangean supercontinent, but may also have involved longer distance, ocean-crossing dispersals between Laurasia and Gondwana across the Tethys Ocean.

Early Triassic (about 250 million years ago) paleobiogeographic distributions of Erythrobatrachus noonkanbahensis (star) and Aphaneramma in Australia (star), Madagascar (circle), Pakistan (square), Svalbard (polygon); and Russia (triangle). Kear et al. (2026).

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Planigale kendricki & Planigale tealei: Two new species of Dasyurid Marsupial from the Pilbara Region of Western Australia.

Among Mammals, the most diverse groups tend to be those which feed on Insects. In Australia, about a quarter of all land Mammals belong to the Dasyuridae, which ate insectivorous and sometimes carnivorous Marsupials. The genus Planigale currently contains four species of Shrew-like insectivorous Marsupials, weighing between 3 and 17 g, which are found across most of the continent, with a fifth species on the island of New Guinea, although molecular studies have suggested that the genus probably contains more diversity than is reflected in this classification. Australia's indigenous Mammals have suffered greatly since the arrival of Europeans, with sharp declines in their numbers still being seen even in parts of the continent with few Human visitors, which makes having an accurate inventory of Australian Mammal species essential to conservation efforts.

The four currently described species of Planigale from Australia, Planigale gilesi, Planigale maculata, Planigale ingrami, and Planigale tenuirostris, are widely distributed in northern and eastern Australia. None of these species are considered to be threatened, but the two most widespread species, Planigale ingrami, and Planigale tenuirostris, have been shown to contain very high levels of genetic diversity, which may indicate that they are actually multiple species with much smaller ranges, and therefore potentially at conservation risk. 

The last major revision of the genus Planigale was carried out in 1976 by zoologist Michael Arche, but since that time genetic methods have become available, with several studies having suggested that there might be one or two undescribed species belonging to the genus present in the Pilbara Region of northerm Western Australia.

In a paper published in the journal Zootaxa on 14 August 2023, Linette Umbrello of the School of Biology and Environmental Science at the Queensland University of Technology, and Collections and Research at the Western Australian Museum, Norah Cooper, also of Collections and Research at the Western Australian Museum, Mark Adams of the Department of Biological Sciences at the University of Adelaide, and the Evolutionary Biology Unit at the South Australian Museum, Kenny Travouillon, again of Collections and Research at the Western Australian Museum, Andrew Baker, also of the School of Biology and Environmental Science at the Queensland University of Technology, and of the Biodiversity and Geosciences Program at Queensland Museum, Mike Westerman of the Department of Environment and Genetics at La Trobe University, and Ken Alpin, again of Collections and Research at the Western Australian Museum, and of the Australian Museum Research Institute at the Australian Museum, formally describe two new species of Planigale from the Pilbara Region.

The approximate distributions of the four currently recognised species of Australian Planigale with Pilbara distributions indicated with arrows. Umbrello et al. (2023).

The first new species described was originally identified as a candidate species in the first ever genetic study of the group, published 1995, in which a team led by Jodie Painter of La Trobe University used the mitochondrial cytichrome b gene to determine the relationships between different species within the genus Planigale. At the time. the candidate species, identified only as Planigale 1, was known from only a single specimen, which was one of only two specimens from Pilbara included in the study (the other specimen was also identified as a new species, Planigale 2, but was later found to belong to a separate genus), but subsequent genetic studies have consistently recovered this species as a separate clade.

Umbrello et al. formally name Planigale 1 as Planigale kendricki, in honour of Peter Kendrick, in recognition of his major contribution to the understanding of the vertebrate fauna of north-western Australia. Planigale kendricki is large for a species of Planigale, with a maximum recorded weight of 12.5 g and a maximum recorded length of 74 mm (excluding the tail). Females are smaller than the males, with a maximum recorded weight of 9.5 g and a maximum recorded length of 69 mm. It is more reddish than other species of the genus, with its back and flanks covered by a thick coat of orange-tan fur with patches of dark brown, while the hair of the underside is grey, changing to yellow or even brown at the tips.

Planigale kendricki. Note the rufous, orange-tan colouration of the fur and the orange eye ring.  Roy Teale in Umbrello et al. (2023).

Planigale kendricki is found across the Pilbara and the surrounding area of northern Western Australia, including the Cape range Peninsula, Ashburton and Gascoyne regions, with specimens reported from the Great Sandy Desert and Little Sandy Desert, Lake Auld, and Mandora near Eighty Mile Beach. It appears to favour areas with exposed bedrock, including sandy plains, scree slopes and rocky creek beds. 

Proposed distribution of Planigale kendricki inferred from specimens at the western Australian Museum (blue dots) that were examined during this study. the border of the Pilbara region is shown by the dashed line in inset A. Umbrello et al. (2023).

The second new species was first identified as a candidate species in a study led by Mark Blacket of La Trobe University and published in 2000, in which a much larger selection of Planigale specimens were examined, and a phylogeny for the genus developed using the 12S rrNA gene sequence. Blacket et al. identified this candidate species as Planigale Mt Tom Price, in reference to the area where it was discovered. This species was also recovered by subsequent genetic studies in 2009, 2016, and 2020, which looked at different gene sets.

Umbrello et al. formally name Planigale Mt Tom Price as Planigale tealei, in honour of Roy Teale, for his support for the work of the Western Australian Museum over many decades, and for collecting many of the specimens on which the description of the species is based. Planigale tealei is small for a species of Planigale, with a maximum male size of 6.1 g and 62.5 mm in length (excluding the tail), and a maximum female size of 4.7 g and 60 mm in length. Its back and sides are covered with a thick, greyish brown coat, paler on the flanks, and pale on the underside.

Planigale tealei (WAM M62896). Linette Umbrello in Umbrello et al. (2023).

Planigale tealei appears to be largely restricted to the Pilbara Region, with very few records outside of the area. It us usually encountered on cracked clay soils in areas with plenty of exposed rocky outcrops, preferring more clay-rich soils.

Proposed  distribution  of Planigale  tealei  inferred  from  specimens  (pink  triangles)  in  the western  Australian Museum that were examined during this study, including southern locality of Waldburg Station. the border of the Pilbara is shown by a dotted line in Inset A. Umbrello et al. (2023).

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Mining giant Rio Tinto forced to apologise after loosing radioactive caesium¹³⁷ capsule in the Western Australian outback.

The mining giant Rio Tinto has been forced to issue an apology to the people of Western Australia, after loosing a capsule containing a small amount of the radioactive isotope caesium¹³⁷ while it was being shipped across the state earlier this month. The capsule served as a radiation source for a device which was able to measure the density of iron within ore samples, which was being transported between the Gudai-Darti Mine, to the north of Newman and the state capital, Perth, a distance of 1400 km, by a specialist contractor brought in by Rio Tinto to undertake the job. The device was inspected at Gudai-Darti and seen to be safe on 12 January 2023, but when inspected in Perth on 16 January is was found that a gauge, one of its four mounting bolts, several screws, and the caesium¹³⁷ capsule had gone missing, apparently shaken loose by the vibration of the truck.

A member of an Incident Management Team in Western Australia which is coordinating the search for the missing radioactive capsule. Western Australia Department of Fire and Emergency Services/Reuters.

The missing capsule is described as silver in colour, 6 mm in diameter and 8 mm long, small enough to raise concerns that it could be caught in the tread of a car tire. The radiation it emits has been described as equivalent to 10 medical X-rays per hour, not threatening to anyone simply driving past, but potentially harmful to anyone remaining within 5 m of the capsule for any length of time, who could potentially suffer burns or even radiation sickness, with the potential for harm to anyone directly handling the capsule being quite high. Authorities in Western Australia are searching for the missing capsule using portable radiation survey meters, which can be mounted on vehicles, and which should be able to detect the capsule from a distance of about 20 m. This method should be able to detect the capsule if it has remained on or close to the road along which it was transported, although if it has moved from this route, for example by being caught on another vehicle, then the task will become much more difficult, and the danger of members of the public having been exposed to harmful levels of radiation much higher.

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Using drones and machine learning to search for an observed meteorite in Australia's Western Nullarbor.

Meteorites can tell us much about the history of the Solar System, having formed in the protoplanetary nebula from which that system formed. They provide useful insights into the physical and chemical compositions of asteroids, and even larger Solar System bodies, but can be hard to find, and begin to be affected by processes on Earth from the moment they arrive. In recent years, fireball observatory networks have been set up in a number of areas, each of which uses a series of cameras to track meteor falls, enabling scientists to track their trajectories and therefore an approximate idea of where any meteorites might have fallen, as well as to calculate their original orbital paths, providing valuable insights into the connection between the composition of meteorites and their origin within the Solar System. However, locating meteorites is still a labourious process, usually involving a team of trained searchers walking in a line 5-10 m apart, sweeping the area of the fall until the meteorite is found, or, more often, the search is abandoned; only about 20% of such searches are successful.

In a paper published on the arXiv database at Cornell University on 3 March 2022, Seamus Anderson, Martin Towner, John Fairweather, Philip Bland, Hadrien Devillepoix, Eleanor Sansom, Martin Cupak, Patrick Shober, and Gretchen Benedix of the Space Science and Technology Centre at Curtin University present the results of a study which used drones and machine learning to search for an observed meteorite in Australia's Western Nullarbor Desert.

The observed meteor fell over the Lintos Paddock area of Kybo Station in Western Australia on the evening of 1 April 2021. This was observed by two cameras operated by Curtain University's Desert Fireball Network, located at Mundrabilla Station and O'Malley Siding, 149 km and 471 km to the east of the end point of the meteor's trajectory. The object was traced from an initial altitude of 87 km until it was only 25 km above the ground, during which time it slowed from 25.4 km per second to 8.4 km per second over a period of 3.1 seconds, while travelling on a slope of 64°. Because of the distance from the observation sites, and the lack of triangulation due to both sites being in the same direction, Anderson et al. created a series of models to predict the final end point of the object.

 

The DFN 09 meteorite fall at Kybo Station, Western Australia. (Clockwise from top) Fireball observations from DFN camera stations at Mundrabilla Station and O’Malley Siding, and their location within Western Australia; The 90% certainty searching area (transparent white), the best fit fall line (red markers), and the location of the recovered meteorite (yellow star); Pre-impact orbit for the DFN 09 meteoroid. Anderson et al. (2022).

Anderson et al. calculated that the object would have a mass of between 150 g and 700g, and identified an area 5.1 km², within which there was a 90% certainty of the meteorite having fallen. This was a high enough certainty to warrant a visit to the area, resulting in a three-day field trip, during which the area was surveyed with a drone and the data from the survey processed by machine learning, resulting in the eventual recovery of a 70 g meteorite.

Favourable and unfavourable prediction distributions from two images. Given a 70% confidence threshold, Image/Distribution (A) will return 3 meteorite candidates, while Distribution (B) will return over 100 candidates. (B)-like images are later used for retraining. For clarity, the number of detections displayed in image (B) is capped at 50. Anderson et al. (2022). 

A DJI M300 drone with a Zenmuse P1 camera was used to study the target area, producing 57 255 images with a 20% overlap. Of these, Anderson et al. were able to process 5096 on site, producing a total of 46 501 000 tiles for their machine learning algorithm to analyse, by comparing patterns to a database of known Nullarbor objects. From these tiles, the algorithm identified 56 384 first stage candidates, which were then studied with a 3x3 grid graphical user interface to eliminate obvious false positives. This reduced the number of candidate tiles to 259 second stage candidates, which were inspected with a second user interface, this time allowing toggling and zooming, to identify more likely objects. This reduced the number of candidates to 38, which were then revisited by the drone for closer inspection, finally reducing the number of candidate objects to four, which were then visited directly by Human researchers.

 

The four stage process for eliminating false positives and verifying meteorite candidates. (From Left to Right) (1) Grid GUI. (2) Zoom-pan GUI. (3) Drone visit. (4) In-person visit.

The meteorite was found less than 50 m from the ideal line predicted by Anderson et al. in the 88th image taken on by the third flight of the drone on the first day of the study. While it has not formally been studied or classified yet, it is a 70 g object measuring approximately 5 x 4 x 3 cm, with a preferentially smoothed side, and a fusion crust typical of chondritic meteorites that have passed through the atmosphere.

 

The recovered meteorite as seen in person (top two), and from the survey drone (bottom one). For scale, a 15 cm long felt pen is placed next to the meteorite (top right). The yellow box in the bottom image is 22 cm on one side. Anderson et al. (2022).

Although their software enabled them to find and recover the meteorite rapidly, Anderson et al. are at pains to emphasise that they have not developed a meteorite-detection program, but rather a program for detecting anomalous objects in images of an area, in this case the Western Nullarbor. As well as the meteorite, the program detected a range of other anomalies, including tin cans, bottles, Snakes, Kangaroos, and piles of bones from multiple Animals. They also note that the program detected equipment used by the surveyors and left around their camp, and which also had not been included in the training data given to the program. They hope that in future the software can be used not just to identify meteorites, but also in fields such as wildlife monitoring, or search and rescue.

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Ingredients for life found in 3.5 billion-year-old fluid inclusions from Pilbara Craton, Western Australia.

Primeval Microbes likely required small organic molecules to act as building blocks for biomass and as catabolic substrates for heterotrophic metabolism. A potential source of such compounds includes recycled and redistributed organic matter from pre-existing biomass. In addition, ample exogenous organic matter probably had been delivered to the early Earth by interplanetary dust particles and meteorites. Experiments have also shown that organic molecules relevant for primordial life can be formed by synthesising organic compounds from inorganic atmospheric gases. As important, endogenous synthesis and processing of organic molecules could have occurred in marine and terrestrial (i.e. hot spring) hydrothermal environments. In such settings, organic molecules may form, or react, at elevated temperatures and pressures within the steady flow of inorganic hydrothermal chemistry (e.g. hydrogen sulphide, carbon dioxide, molecular hydrogen). One hypothesis on organic synthesis at hydrothermal sites suggests that the reaction of iron(II) sulphide to pyrite with hydrogen sulphide drives the reduction of carbon dioxide to organic molecules. Moreover, a primordial carbon fixation mechanism involving the reaction of carbon monoxide with methanethiol on catalytic metal (nickel or iron) sulphide surfaces could be demonstrated in the laboratory under hydrothermal conditions. This experiment produced an activated form of acetic acid that represents a plausible building block for further organic synthesis, for example, into acyl lipids. As yet, however, such distinctive organic molecules have not been found in rocks that directly testify to the emergence of life on our planet.

The roughly 3.5 billion-year-old Dresser Formation (Pilbara Craton, Western Australia) is one of the most important windows into hydrothermal habitats on early Earth. The rocks are only mildly metamorphosed (prehnite-pumpellyite to lower greenschist facies) and still preserve numerous putative biosignatures, including Stromatolites, microfossils, and isotopic anomalies. Further, cherts and barites of the Dresser Formation contain kerogenous organic material of supposedly biological origin. Detailed field mapping, petrographic observations, and mineralogical analyses revealed that the Dresser Formation was formed in a hydrothermal setting, most likely a volcanic caldera. Thus, it appears plausible that organisms in the Dresser environments grew chemotrophically, fuelled by hydrothermal fluids that delivered inorganic and organic substrates. Indeed, stable carbon and sulphur isotopic anomalies indicate methanogenic and sulphur-disproportionating Microbes as key players in these early Microbial communities, although the exact metabolisms still await further evidence and testing.

Cherts and barites of the Dresser Formation contain abundant primary fluid inclusions, that is, fluids and/or gases entrapped in minerals. These fluid inclusions represent a valuable archive, as their chemistry can potentially be preserved for billions of years. Barite appears to be a particularly robust host mineral because of its low solubility and high stability under a wide range of pressure, temperature and redox conditions. Therefore, fluid inclusions in the Dresser barites are excellent candidates in the search for organic molecules that once supported Microbial life. Previous work identified water, carbon dioxide, hydrogen sulphide, and minor methane as the main inorganic constituents of the fluid inclusions in Dresser barites. However, the content of organic molecules, potential key ingredients for early life, is as yet unknown.

In a paper published in the journal Nature Communications on 17 February 2021, Helge Mißbach of Geobiology at the University of Göttingen, and Geobiology at the University of Cologne, Jan-Peter Duda, also of Geobiology at the University of Göttingen, the 'Origin of Life' Group at the Göttingen Academy of Sciences and Humanities, and Sedimentology & Organic Geochemistry at the University of Tübingen, Alfons van den Kerkhof of Applied Geology at the University of Göttingen, Volker Lüders of the GFZ German Research Centre for Geosciences, Andreas Pack of the Isotope Geology Divison at the University of Göttingen, Joachim Reitner, also of Geobiology at the University of Göttingen, and the 'Origin of Life' Group at the Göttingen Academy of Sciences and Humanities, and Volker Thiel, once again of Geobiology at the University of Göttingen, report on the presence of biologically-relevant primordial organic molecules in primary fluid inclusions trapped in barites of the roughly 3.5 billion-year-old Dresser Formation. To explore the full range of volatiles, Mißbach et al. combined gas chromatography–mass spectrometry, microthermometry, fluid inclusion petrography, and stable isotope analysis. Their findings reveal an intriguing diversity of organic molecules with known or inferred metabolic relevance and provide a strong clue as to how ancient hydrothermal fluids sustained Microbial life about 3.5 billion years ago.

The Dresser Formation contains thick barite units with colours ranging from white and grey to black. Black barites exhibit coarse crystalline textures and yield a strong hydrogen sulphide odour when freshly crushed. The sedimentary black barite studied here was sampled in the Dresser mine, where it was interbedded with originally sulphidic Stromatolites. Field and petrographic evidence clearly suggest a primary origin of the barite (e.g. no progressive replacement of stromatolite interbeds, no relicts of potential precursor materials within the barite). Thin section analysis revealed the presence of abundant primary and rare secondary inclusions. Most primary fluid inclusions are small (about 10 μm), translucent, and often oriented parallel to planes of barite crystals, thereby tracing succeeding growth phases. Morphologies of some fluid inclusions indicated necking down, which is a typical modification under stress conditions after crystallisation. These inclusions are typically stretched and may split up in segments that then usually show different composition and density.

 

Study area and field evidence. Location of the Dresser mine in Western Australia near Marble Bar (a) and black barite associated with originally sulphidic Stromatolites at the sampling site (b) and in the working area (c). The close association between the inclusion-bearing black barites and Stromatolites suggests that hydrothermal fluids might have influenced ancient microbial communities. Mißbach et al. (2021).

The fluid inclusions were analysed optically on a heating-freezing stage and by Raman spectroscopy. The black barites contain aqueous carbonic-sulfuric and non-aqueous carbonic-sulfuric fluid inclusions (hereafter, aqueous, and non-aqueous, respectively). Aqueous inclusions show highly variable water volume fractions of 0.1–1. At room temperature, they typically exhibit a double meniscus, indicating the presence of three phases: water + another (carbon dioxide–hydrogen sulphide-rich) liquid + vapour. In some cases, the other liquid is only visible during cooling runs. In comparison, non-aqueous fluid inclusions usually contain a carbon dioxie–hydrogen-sulphide-rich liquid and a vapour phase, although the liquid phase is sometimes absent at room temperature.

 

Fluid inclusions in representative black barites from the Dresser mine. (a), (b) Thin section images (reflected light) showing primary fluid inclusion trails parallel to barite crystal growth bands (marked by black arrows). (c) Thin section image (transmitted light) showing primary fluid inclusions which are dispersed or oriented parallel to barite crystal growth bands (exemplified by dashed line). The image also shows a minor secondary inclusion trail (marked by black arrow). (d) Thick section image (transmitted light) of an aqueous carbonic-sulfuric fluid inclusion containing three volatile phases (including hydrogen sulphide), plus pyrite, native sulfur, and strontianite as solid phases. (e) Thick section image (transmitted light) of a non-aqueous fluid inclusion bearing a vapour phase, native sulphur, and kerogen. These fluid inclusions are usually rich in hydrogen sulphide. V vapour/gas, Lw liquid water, L other liquid (e.g. CO2carbon dioxide). Organic compounds and gases preserved in these primary fluid inclusions could have provided a substrate to primordial microbial life in the Dresser Formation. Mißbach et al. (2021).

Both types of fluid inclusions typically contain solid daughter phases. Aqueous inclusions usually contain strontianite and sulphur as daughter crystals. Varieties with pure carbon dioxide in the vapour phase (volume fractions of about 0.9) may additionally include anatase, pyrite, and possibly also halite. In non-aqueous inclusions, typical daughter phases are sulphur, kerogen and, in few cases, halite.

The main gas components in both fluid inclusion types are carbon dioxide and hydrogen sulphide, accompanied by minor amounts of methane, nitrogen, and carbonyl sulphide. Aqueous fluid inclusions contain less hydrogen sulphide than non-aqueous fluid inclusions (0–24% by molarity and 21–36% by molarity, respectively). Furthermore, aqueous fluid inclusions typically enclose up to 1% by molarity nitrogen, which is not present in non-aqueous fluid inclusions. Instead, non-aqueous fluid inclusions additionally contain small amounts of methane (less than 2% by molarity).

 

Gas compositions of fluid inclusions in black barites as measured by Raman analysis. 0 % hydrogen sulphide (H₂S)  implies that the fluid inclusion largely contains carbon dioxide (CO₂). FI fluid inclusions. Mißbach et al. (2021).

Aqueous fluid inclusions typically reveal liquid compositions ranging from pure water to more saline solutions with 14% by weight sodium chloride-equivalents. Higher salinities of up to 25% by weight sodium chloride-equivalents are rare. The corresponding ice melting temperatures vary between 0°C and −26°C (peak at −7 °C). Aqueous fluid inclusions form clathrates upon freezing and subsequent melting between 7°C (pure carbon dioxide) and 20°C (hydrogen sulphide-rich). Total homogenisation temperatures, describing the minimum temperature of fluid entrapment, range from 100 to 195°C, with a maximum between 110 and 150°C. Most fluid inclusions decrepitate at temperatures of over 230°C.

 

Bar plots showing phase transition temperatures. From top to bottom: (i) homogenisation of the non-aqueous phase (total homogenisation temperature carbon dioxide-hydrogen sulphide), (ii) melting of carbon dioxide and hydrogen sulphide (melt temperature carbon dioxide-hydrogen sulphide), (iii) ice and clathrate melting (melt temperature ice/(melt temperature ice, metastable, and melt temperature clathrates, respectively), (iv) total homogenisation and decrepitation (total homogenisation and total decrepitation, respectively) temperatures. C, critical; V, vapour, L, liquid. Mißbach et al. (2021).

Non-aqueous fluid inclusions show total homogenisation temperatures (carbon dioxide-hydrogen sulphide) between 16 and 38°C. Those containing higher concentrations of hydrogen sulphide typically homogenise at the higher end of this range, that is, above the critical temperature of carbon dioxide (31.1°C). Phases usually homogenise to liquid, and only rarely to the gas or critical phase. During cooling runs, the subsequent melting of solid carbon dioxide and hydrogen sulphide can be observed at lower temperatures compared to the pure compounds (−56.6°C and −83.6°C, respectively).

Mißbach et al.'s data demonstrate that the majority of aqueous and nonaqueous inclusions formed during crystal growth (i.e. primary inclusions). Thus, fluids must have been immiscible at the time of encapsulation, and experienced identical trapping and homogenisation temperatures (i.e. heterogeneous trapping). Therefore, no pressure correction is necessary.

Online analyses of black barite fragments using thermal decrepitation-gas chromatography–mass spectrometry yielded high amounts of carbon dioxide, hydrogen sulphide, and water, thus confirming results from Raman analysis on fluid inclusions. The diversity and intensity of compounds was considerably higher in the 250°C than in the 150°C experiment. This finding is consistent with the microthermometry data revealing that most fluid inclusions remain intact up to about 230°C.

 

Total ion current chromatogram of volatile compounds from black barite fluid inclusions as detected by thermal decrepitation/desorption thermal decrepitation-gas chromatography–mass spectrometry analysis at 250 C. Inserts (a), (b) represent enlargements of respective areas in the chromatogram marked by dashed lines. Triangles denote oxygen-bearing compounds, circles denote aromatic hydrocarbons and stars denote sulfur-bearing compounds. n-Hexane (Hex) was used as a retention time standard (RT std.). COS carbonyl sulphide, Ea ethanal, MT methanethiol, Bu but-1-ene, Pa prop-2-enal, Pa’ propanal, ET ethanethiol, MSM (methylsulfanyl)methane, Po propan-2-one, Ba but-2-enal, Ox oxolane, TP thiophene, B benzene, Ac acetic acid, TL thiolane. Note the presence of methanethiol and acetic acid, the stable building blocks of activated acetic acid. Mißbach et al. (2021).

Offline analysis using solid phase micro extraction-gas chromatography–mass spectrometry revealed numerous organic molecules containing oxygen (aldehydes, ketones, acetic acid, oxolane) and/or sulphur (thiophene, thiols, organic polysulphanes), along with some aromatic hydrocarbons (e.g. benzene, alkylbenzenes). Compounds detected with both analytical techniques showed a lower abundance in olid phase micro extraction-gas chromatography–mass spectrometry as compared to thermal decrepitation-gas chromatography–mass spectrometry at 250°C. On the other hand, solid phase micro extraction-gas chromatography–mass spectrometry yielded a considerably greater diversity of compounds, especially in the higher molecular weight range. The absence of carbon doxide and hydrogen sulphide in the solid phase micro extraction-gas chromatography–mass spectrometry runs is due to an analytical bias, as these compounds do not adsorb onto the solid phase micro extraction fibre.

 

Total ion current chromatogram of volatile compounds from black barite fluid inclusions as obtained by solid phase micro extraction solid phase micro extraction-gas chromatography–mass spectrometry. Inserts (a)–(c) represent enlargements of respective areas in the chromatogram marked by dashed lines. Triangles denote oxygen-bearing compounds, circles denote aromatic hydrocarbons and stars denote sulphur-bearing compounds. n-Hexane (Hex) was used as a retention time standard (RT std.). COS carbonyl sulfide, Ea ethanal, MT methanethiol, Pa prop-2-enal, Pa’ propanal, ET ethanethiol, MSM (methylsulfanyl)methane, Po propan-2-one, Ba but-2-enal, Ox oxolane, Bo butan-2-one, TP thiophene, B benzene, Ac acetic acid, MB 3-methylbutan-2-one, Mxp 1-methoxypropan-2-ol, Pe pentanal, MDSM (methyldisulfanyl)methane, To toluene, MP 4-methylpentan-2-one, Ha hexanal, MEDS (methyldisulfanyl)ethane, Xy I p-xylene, Xy II m-xylene, Pac 1-methoxyprop-2-yl acetate, Xy III o-xylene, Sty styrene, CH cyclohexanone, Hp heptanal, BA benzaldehyde, MTSM (methyltrisulfanyl)methane, TMB I 1,3,5-trimethyl benzene, TMB II 1,2,4-trimethyl benzene, MH 6-methylheptan-3-one, TMB III 1,2,3-trimethyl benzene. Note the higher diversity of compounds as compared to thermal decrepitation/desorption analysis. Oxygen- and sulfur-bearing organic compounds may have provided substrates for microbial life in the Dresser Formation. Mißbach et al. (2021).

The mean total organic carbon content of the black barite is 0.31% by weight. Stable carbon isotope analysis revealed a mean proportional value of −27.6±0.6‰ carbon¹³ in total organic carbon, compared to the Vienna Pee Dee Belemnite standard. Offline analysis revealed porportions of carbon¹³ and oxygen¹⁶ in carbon dioxide values of −10.0±0.3‰ and 34.1±0.6‰, respectively, compared to the Vienna Pee Dee Belemnite and Vienna Standard Mean Ocean Water standards. Online analyses yielded porportions of carbon¹³ in carbon dioxide values ranging from −14.3 to −8.9±0.3 ‰ for black barites (mean = –10.3 ‰) and from −8.6 to −4.0±0.3‰ for grey barites (mean = −6.3 ‰). Thus, black barites are consistently more depleted in carbon¹³ than their grey counterparts. In all cases, methan and nitrogen contents were too low for stable isotope analyses (less than 2% by molarity).

 

Molecular structures of oxygen-bearing compounds, aromatic hydrocarbons, and sulphur-bearing compounds found in black barite fluid inclusions. Mißbach et al. (2021).

The Black barites studied by Mißbach et al. classify as primary hydrothermal sediments that precipitated from discharging fluids. This interpretation is additionally supported by the facts that (i) the originally sulphidic Stromatolite interbeds are still largely intact and show no indications for a progressive replacement by barite and (ii) that the barite does not contain relicts of potential precursor materials. Mißbach et al.'s  observations are therefore consistent with earlier studies that argued for a primary, synsedimentary origin of the Dresser barites analysed herein (i.e. precipitation in surface environments linked to hydrothermal activity).

 

Distribution of stable carbon isotope signatures of carbon dioxide from black and grey barite fluid inclusions. Reproducibility of the stable isotope measurements is 0.3‰. A total of 11 black barite samples and 11 grey barite samples was analysed. The relatively low proportional carbon¹³ values in the black barites possibly reflect the addition of a biomass-derived carbon component to the fluids. Mißbach et al. (2021).

Barite is highly chemically stable under a wide range of geological conditions. Hence, barite-hosted fluid inclusions can preserve information on the original composition of hydrothermal fluids. The black and grey barites from the Dresser Formation primarily grew as coarse crystals and contain abundant primary fluid inclusions. Most fluid inclusions show no indication of post-entrapment modification. The results are reproducible and total homogenisation temperature values (100–195°C) are internally consistent for different coevolutionary fluid inclusions. The measured total homogenisation temperature is in line with (i) formation temperatures estimated for coexisting cherts (100–200°C), and (iii) maximum formation temperatures of barite-hosted fluid inclusions in a modern hydrothermal system (the Jade hydrothermal field in the Izena Hole, mid-Okinawa Trough, 150–200°C).

The aqueous and non-aqueous fluid inclusions distinguished herein appear to include those described in earlier studies. Particularly key-characteristics such as sizes (5–30 μm), ice and clathrate melting temperatures (−7.5 to −0.6°C and −0.9 to 19.2°C, respectively), and the fundamental volatile inventories (carbon dioxide, water, hydrogen sulphide, methane) are all remarkably similar. A notable exception is the presence of trace amounts of nitrogen in some of the aqueous fluid inclusions, which has not been reported previously.

The presence of aqueous and non-aqueous fluid inclusions can be explained by the presence of two coexisting fluids at the time of trapping as a result of phase separation from boiling fluids during cooling (effervescence). Hence, the major fluid composition of the black barites can be considered primary. However, there are indications that a few fluid inclusions were locally modified immediately after emplacement (e.g. necking down after crystallisation), explaining the wide variations observed in total homogenisation temperatures. This information is not relevant to the interpretation of the fluids as being primary, because they would be trapped again instantly with their overall composition remaining unchanged.

Organic molecules detected by gas chromatography–mass spectrometry are derived from the fluid inclusions as evidenced by (i) clean pre-analysis blanks, (ii) retrieval of products exclusively after grinding of barite, (iii) reproducibility of the results from five thermal decrepitation-gas chromatography–mass spectrometry and seven solid phase micro extraction-gas chromatography–mass spectrometry experiments, (iv) presence of highly volatile compounds in gas chromatography–mass spectrometry analyses, (v) consistency of data obtained by independent analytical techniques (Raman spectroscopy vs. gas chromatography–mass spectrometry), (vi) temperature dependency of product yields, meaning that higher temperature analyses above the decrepitation temperature of fluid inclusions result in higher abundances (thermal decrepitation-gas chromatography–mass spectrometry 150°C vs. thermal decrepitation-gas chromatography–mass spectrometry 250°C), and (vii) absence of molecular contamination indications. Together, these multiple lines of evidence strongly suggest that the analysed compounds derived from the fluid inclusions, while a minor contribution of organic compounds from the rock matrix cannot entirely be ruled out. This result adds to earlier studies, which demonstrated that fluid inclusions form closed systems that can preserve molecules even in billion-year-old metamorphic rocks.

Organic molecules detected by thermal decrepitation-gas chromatography–mass spectrometry and solid phase micro extraction-gas chromatography–mass spectrometry display major differences in diversity and abundance. Solid phase micro extraction probably provides a more authentic picture of the compounds contained in the fluid inclusions, because no heating to more than 50°C is applied before gas chromatography–mass spectrometry analysis. In contrast, thermal decrepitation resulted in abundant sulphur dioxide formation during heating to higher temperatures (250°C experiment), reflecting thermally driven artefact formation by reaction of the components in the interior of the fluid inclusions. Additionally, and even more important, the mild solid phase micro extraction offline approach can be applied on much greater sample amounts (gram vs. milligrams), resulting in detectable yields of trace compounds that are indiscernible with the thermal decrepitation approach.

The Dresser Formation formed in a hydrothermal environment. Hence, compounds entrapped in barite-hosted fluid inclusions may have been derived from abiotic sources. Indeed, gaseous compounds such as sulphur dioxide, carbon dioxide, hydrogen sulphide, carbonyl sulphide, carbon disulphide, and (methylsulphanyl)methane are known to be delivered to surface environments via volcanic outgassing. Functionalised lipid-like organic molecules such as ketones, aldehydes, carboxylic acids, and alcohols can be formed by Fischer–Tropsch-type processes under hydrothermal conditions. Further compounds of possibly abiotic origin are acetic acid and organic sulfur molecules (e.g. thiols, organic polysulphanes). These molecules may be synthesized in the presence of sulphide catalysts and with carbon disulphide or carbon dioxide as a carbon source. Extraterrestrial delivery by meteorites could have provided an additional source for many of the observed compounds (e.g. carbonyl sulphide, carbon disulphide, hydrogen sulphide, methanethiol, benzaldehyde, acetic acid, benzene, toluene, various aldehydes, and ketones).

While many compounds observed in the barite-hosted fluid inclusions from the Dresser Formation are consistent with an abiotic origin, the Dresser Formation also contains a variety of evidence for life. Thus, biology is another potential source for the observed compounds. In fact, organisms synthesise most lipids on modern Earth, and proportional carbon¹³ signatures of kerogen in the black barite (roughly –28 ‰) are in good accordance with biological carbon fixation. Furthermore, compounds such as hydrogen sulphide, carbonyl sulphide, carbon disulphide, (methylsulphanyl)methane, (methyldisulphanyl) methane, and thiols are typically formed during microbial sulphur cycling in modern environments, and there is isotopic evidence for the presence of sulfur-processing metabolisms during Dresser times. 

Taken together, it is likely that the barite-hosted fluid inclusions contain mixtures of various abiotic and biotic compounds. Such contributions from different sources would plausibly explain the contrasting proportional carbon¹³ signatures of carbon dioxide in grey and black barites. Carbon dioxide released from grey barites exhibits a mean proportional carbon¹³ value of –6.3‰, which might be indicative of a magmatic source (typically between −2 and −8‰). In contrast, lower proportional carbon¹³ values of −10.3‰ in carbon dioxide from black barites might fingerprint a biomass-derived carbon component that had been converted to carbon dioxide via Bacterial and/or thermochemical sulphate reduction before it was absorbed and transported by fluids. The processing, re-distribution, and mixing of fluids from different sources is well known from modern and ancient hydrothermal systems (hydrothermal pump).

It is widely assumed that hydrothermal processes fuelled primeval life on Earth, but it is difficult to pinpoint the exact nature of such relationships in the Archaean rock record. The fluid inclusion-bearing black barites are interbedded with Stromatolites, suggesting that hydrothermal fluids may have influenced the ancient Microbial communities. Indeed, many compounds discovered in the barite-hosted fluid inclusions (e.g. carbonyl sulphide, carbon disulphide, acetic acid, (methylsulphanyl)methane, (methyldisulphanyl)methane, thiols, methane) would have provided ideal substrates for the sulfur-based and methanogenic microbes previously proposed as players in the Dresser environment. For instance, acetic acid may have fuelled acetoclastic methanogenesis, while organic sulphides such as methanethiol and (methylsulphanyl)methane might have served as substrates for fermenting methanogenic Bacteria. This hypothesis is in full agreement with isotopic evidence indicating the existence of methanogenic and sulphur-cycling Microbes in Dresser environments. The activity of sulphate reducing or sulphur disproportioning Bacteria could also account for the presence of abundant pyrite in the originally sulphidised Dresser Stromatolites. Thus, Mißbach et al.'s findings provide a strong clue that Microbial life associated with the black barites of the Dresser Formation was (partly at least) fuelled by hydrothermal fluid flow.

In addition to potential nutrients and/or substrates, hydrothermal fluids captured in the Dresser fluid inclusions contain molecules closely related to putative key agents in the emergence of life. It has been proposed that carbon monoxide and methanethiol can react in the presence of catalytic metallic sulphides to methyl thioacetate. This compound, also known as activated acetic acid, was proposed as being important for the formation of lipids under primordial conditions and as an energy source for early Microbial metabolisms. Whereas this highly energetic molecule is readily hydrolysed and cannot be preserved over geological time, our data evidence the presence of its stable building blocks, methanethiol and acetic acid, in the Dresser fluids. In other words, essential ingredients of methyl thioacetate, a proposed critical agent in the emergence of life, were available in the Dresser environments.

Mißbach et al.'s data provide the first detailed picture of the organic composition of primordial fluids that had evidently been available for the ancient Microbes roughly 3.5 billion years ago. These fluids delivered ample catabolic substrates for chemoheterotrophic metabolisms. In addition, they might have conveyed the building blocks for chemoautotrophic carbon fixation and, thus, anabolic uptake of carbon into biomass. Taken together, Mißbach et al.'s data strongly support the idea that hydrothermal fluids supplied a fertile substrate for early Microbial life on Earth.

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