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1. The recovery of the deep biosphere at the Chicxulub impact crater

   Coolen, M. (January 2018, American Geophysical Union Fall Meeting)

   The Chicxulub crater, Mexico, is the site of the asteroid impact that led to the end-Cretaceous mass extinction. While impact events are known to be able to cause severe disruption to surface-dwelling organisms, the effects of such catastrophic perturbations on the deep biosphere are not known. Deep ocean drilling into the peak ring of the Chicxulub impact crater (IODP expedition 364) in 2016 allowed us to study the modern deep biosphere within the (a) high-porosity melt-bearing impact breccia/suevite (617-740 mbsf) emplaced within a day or so of the Cenozoic, (b) the overlying low porosity post-impact marine Cenozoic carbonates (504-617mbsf), and the impacted and fractured granitic basement (740-1334 mbsf). The microbial biomass (~10 cells/g wet weight) was highest in the upper suevite, in underlying non-granitic subvolcanic pre-impact basanite, and at the intercalation of suevite and impact melt rock. Pre-impact sterile conditions of the uplifted granitic basement rocks and mineralogical evidence of impact-induced sterilization suggest that the basement rocks have only been amenable to microbial colonization for less than 66 Myr. Enrichments at in situ 50-60 °C show the presence of heterotrophic lifestyles in the suevite and bacterial sulfate reduction extending into the top of the granitic basement. Cultivation-independent 16S diversity profiling revealed the presence of heterotrophic (fermentative) as well as autotrophic C-fixing thermophilic bacteria in the organic-rich (up to 4 wt % total organic carbon; TOC) Cenozoic sediments. The organic-lean suevite (< 0.1% TOC) showed the unique presence of sequences related to thermophilic Synechococcus (cyanobacteria) and S-oxidizing green sulfur bacteria (chlorobi), and Chloroflexi often associated with organic-poor deep-sea sediments. Alphaproteobacteria, predominated in the upper part of the granitic basement (<1000 mbsf), while putative manganeseoxidising Bacilli (Firmicutes) predominated in the melt-rich granitic basement (>1200 mbsf). Our data suggest that the catastrophe that led to the end-Cretaceous mass extinction caused geological disruption and recolonization of microbial life in the deep subsurface biosphere at the Chicxulub impact site. 

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2. Chicxulub: Drilling the K-Pg Impact Crater

   https://doi.org/10.14379/iodp.proc.364.2017  

   Morgan, J.; Gulick, S.; Mellett, C.L.; Green, S.L. (December 2017, Proceedings of the International Ocean Discovery Program)

   null (Ed.)

   The Chicxulub impact crater, on the Yucatán Peninsula of México, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic peak ring. Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on the Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic. During International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364, Paleogene sedimentary rocks and lithologies that make up the Chicxulub peak ring were cored to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of post-impact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Other key targets included sampling the transition through a rare midlatitude Paleogene sedimentary succession that might include Eocene and Paleocene hyperthermals and/or the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of suevite, impact melt rock, and basement rocks in the peak ring; the sedimentology and stratigraphy of the Paleocene–Eocene Chicxulub impact basin infill; the geo- and thermochronology of the rocks forming the peak ring; and any observations from the core that may help constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical properties measurements on the core and wireline logs acquired during Expedition 364 will be used to calibrate geophysical models, including seismic reflection and potential field data, and the integration of all the data will calibrate models for impact crater formation and environmental effects. The drilling directly contributes to IODP Science Plan goals: Climate and Ocean Change: How does Earth’s climate system respond to elevated levels of atmospheric CO2? How resilient is the ocean to chemical perturbations? The Chicxulub impact represents an external forcing event that caused a 75% species level mass extinction. The impact basin may also record key hyperthermals within the Paleogene. Biosphere Frontiers: What are the origin, composition, and global significance of subseafloor communities? What are the limits of life in the subseafloor? How sensitive are ecosystems and biodiversity to environmental change? Impact craters can create habitats for subsurface life, and Chicxulub may provide information on potential habitats for life, including extremophiles, on the early Earth and other planetary bodies. Paleontological and geochemical studies at ground zero will document how large impacts affect ecosystems and biodiversity. Earth Connections/Earth in Motion: What mechanisms control the occurrence of destructive earthquakes, landslides, and tsunami? Drilling into the uplifted rocks that form the peak ring will be used to groundtruth numerical simulations and model impact-generated tsunami, and deposits on top of the peak ring and around the Gulf of México will inform us about earthquakes, landslides, and tsunami generated by Chicxulub. These data will collectively help us understand how impact processes are recorded in the geologic record and their potential hazards. IODP Expedition 364 was a Mission Specific Platform expedition designed to obtain subseabed samples and downhole logging measurements from the post-impact sedimentary succession and the peak ring of the Chicxulub impact crater. A single borehole (Hole M0077A) was drilled into the Chicxulub impact crater on the Yucatán continental shelf, recovering core from 505.70 to 1334.69 meters below seafloor (mbsf) with ~99% core recovery. Downhole logs were acquired for the entire depth of the borehole. 

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3. Expedition 364 Preliminary Report: Chicxulub: drilling the K-Pg impact crater

   https://doi.org/10.14379/iodp.pr.364.2017  

   Gulick, S.; Morgan, J.; Mellett, C.L. (February 2017, Preliminary report)

   null (Ed.)

   The Chicxulub impact crater, México, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic peak ring. Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on the Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic. During International Ocean Discovery Program (IODP) Expedition 364, Paleogene sediments and lithologies that make up the Chicxulub peak ring were cored to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of post-impact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Other key targets included sampling the transition through a rare midlatitude section that might include Eocene and Paleocene hyperthermals and/or the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of the impact breccias, melt rocks, and peak-ring rocks; the sedimentology and stratigraphy of the Paleocene–Eocene Chicxulub impact basin infill; the chronology of the peak-ring rocks; and any observations from the core that may help us constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical property measurements on the core and wireline logs acquired during Expedition 364 will be used to calibrate geophysical models, including seismic reflection and potential field data, and the integration of all the data will calibrate impact crater models for crater formation and environmental effects. The proposed drilling directly contributes to IODP Science Plan goals: Climate and Ocean Change: How resilient is the ocean to chemical perturbations? The Chicxulub impact represents an external forcing event that caused a 75% level mass extinction. The impact basin may also record key hyperthermals within the Paleogene. Biosphere Frontiers: What are the origin, composition, and global significance of subseafloor communities? What are the limits of life in the subseafloor? How sensitive are ecosystems and biodiversity to environmental change? Impact craters can create habitats for subsurface life, and Chicxulub may provide information on potential habitats for life, including extremophiles, on the early Earth and other planetary bodies. Paleontological and geochemical studies at ground zero will document how large impacts affect ecosystems and effects on biodiversity. Earth Connections/Earth in Motion: What are the composition, structure and dynamics of Earth’s upper mantle? What mechanisms control the occurrence of destructive earthquakes, landslides, and tsunami? Mantle uplift in response to impacts provides insight into dynamics that differ between Earth and other rocky planets. Impacts generate earthquakes, landslides, and tsunami, and scales that generally exceed plate tectonic processes yield insight into effects, the geologic record, and potential hazards. IODP Expedition 364 was a Mission Specific Platform expedition to obtain subseabed samples and downhole logging measurements from the sedimentary cover sequence and peak ring of the Chicxulub impact crater. A single borehole was drilled into the Chicxulub impact crater on the Yucatán continental shelf, recovering core from 505.7 to 1334.73 m below seafloor with ~99% core recovery and acquiring downhole logs for the entire depth. 

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4. Expedition 364 Scientific Prospectus: Chicxulub: drilling the K-Pg impact crater

   https://doi.org/10.14379/iodp.sp.364.2016  

   Gulick, S.; Morgan, J.; Mellett, C.L. (March 2016, Scientific prospectus)

   null (Ed.)

   The Chicxulub impact crater in Mexico is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic “peak ring.” Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 y of intense debate, we are still striving to answer the question as to why this impact was so catastrophic. International Ocean Discovery Program (IODP) Expedition 364 proposes to core through the peak ring of the Chicxulub impact crater to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of postimpact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Of additional interest is the transition through a rare midlatitude record of the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of impact breccias, melt rocks, and peak-ring rocks; the sedimentology and stratigraphy of the Cenozoic sequence; and any observations from the core that would help us constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical property measurements on the core and wireline logs will be used to calibrate geophysical models, including seismic reflection data. Proposed drilling directly contributes to the IODP science plan initiatives (1) Deep Biosphere and the Subseafloor Ocean and (2) Environmental Change, Processes and Effects, in particular the environmental and biological perturbations caused by the Chicxulub impact. Expedition 364 will be implemented as a mission-specific platform expedition to obtain subseabed samples and downhole logging measurements from the peak ring of the Chicxulub impact crater. The expedition aims to core a single borehole as deep as 1500 meters below seafloor (mbsf) to recover rock cores from above and into the Chicxulub impact crater preserved under the Yucatán continental shelf. 

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5. Active methylotrophic methanogenesis by a microbial consortium enriched from a terrestrial meteorite impact crater

   https://doi.org/10.1128/mbio.03017-25  

   van_Dam, Femke; Westmeijer, George; Rezaei_Somee, Maryam; Ketzer, Marcelo; Kietäväinen, Riikka; Ono, Shuhei; Bertilsson, Stefan; McIntosh, Jennifer C; Dopson, Mark; Drake, Henrik (January 2026, mBio)

   Kostka, Joel E (Ed.)

   ABSTRACT Microbial methane generation (methanogenesis) is an important metabolic process in the terrestrial deep biosphere and is an analog to early Earth as it is proposed to be one of the most ancient metabolisms on Earth. Signs of methanogenesis in meteorite impact craters are of particular interest in this respect as these settings are proposed hot spots for deep microbial colonization of the upper crust. Yet, reports of active deep rock-hosted methanogenesis are scarce, particularly for methylotrophic methanogenesis, while reports from terrestrial meteorite impact craters are completely lacking. Here, we used indigenous communities in cultures enriched from 400-m deep fluids to confirm and characterize active methane production from several carbon donors, including indigenous oil, in a terrestrial impact crater at Siljan, Sweden. Metagenomic and metatranscriptomic data of the methane-producing cultures revealed a consortium dominated byAcetobacteriumsp. KB-1 andCandidatusMethanogranum gryphiswaldense, mediating methanogenesis solely via the methyl-reduction pathway, and resulting in a δ¹³C_{methanol-methane}isotope enrichment of up to 98.6‰. These results provide insights into methylotrophic methanogenesis in deep subsurface environments in general, and in particular in fractured meteorite impact structures.IMPORTANCEThis study revealed that microbes enriched from groundwater in a 380-m deep borehole within the Siljan meteorite impact crater in Sweden were capable of producing methane, a key greenhouse gas. This is especially significant because it is the first proof of active methanogens in an impact crater and showing a specific pathway of methane production—methylotrophic methanogenesis—is present in the deep terrestrial subsurface, an environment that is typically hard to study. These findings shed light on life in extreme conditions on Earth and show that meteorite craters can be biological hotspots, rich with ancient life processes. 

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