Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution.

The near-Earth carbonaceous asteroid (162173) Ryugu is expected to contain volatile chemical species that could provide information on the origin of Earth's volatiles. Samples of Ryugu were retrieved by the Hayabusa2 spacecraft. We measured noble gas and nitrogen isotopes in Ryugu samples and found that they are dominated by presolar and primordial components, incorporated during Solar System formation. Noble gas concentrations are higher than those in Ivuna-type carbonaceous (CI) chondrite meteorites. Several host phases of isotopically distinct nitrogen have different abundances among the samples. Our measurements support a close relationship between Ryugu and CI chondrites. Noble gases produced by galactic cosmic rays, indicating a ~5 million year exposure, and from implanted solar wind record the recent irradiation history of Ryugu after it migrated to its current orbit.

Data on atmospheric 129I concentrations and 129I/137Cs ratios for suspended air particulate matter dispersed in eastern Japan just after the 2011 nuclear accident in Fukushima, Japan.

Data of the atmospheric activity concentrations (in Bq/m3) of 129I dispersed into the environment as aerosol immediately after the nuclear accident at Fukushima Daiichi Nuclear Power Plant in 2011 are presented. The radioactivity of 129I was determined in suspended particulate matter (SPM) collected on filter tapes at 41 SPM monitoring sites in Fukushima and other prefectures in eastern Japan including the metropolitan area. For quantitative determination of 129I in SPM samples by accelerator mass spectrometry (AMS), 129I was chemically separated. Prior to the 129I measurement, the 137Cs activity was determined for the same SPM sample by gamma-ray spectrometry using Ge-semiconductor detectors. Combining activity concentrations of the two nuclides, an activity ratio of 129I/137Cs (in Bq/Bq) was calculated for each SPM sample. In our research project, atmospheric activity concentrations of 129I and 137Cs, and their activity ratios were obtained for 920 SPM samples. Scientific discussion related to those data was described in the research article entitled "Time-series variations of atmospheric 129I concentrations and 129I/137Cs ratios in eastern Japan just after the 2011 nuclear accident in Fukushima, Japan" (Ebihara et al. 2022), where 363 data sets were presented. The remaining 557 data sets are presented in this article, so this data article makes up for the original research article (Ebihara et al. 2022). Blank values were obtained for whole analytical procedure. In addition, those for reagents and filters (both bland-new and used filters) were analyzed for assessing the contribution of the 129I activity from these samples. Those data also are presented in this article.

First asteroid gas sample delivered by the Hayabusa2 mission: A treasure box from Ryugu.

The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after the recovery, the gas species retained in the sample container were extracted and measured on-site and stored in gas collection bottles. The container gas consists of helium and neon with an extraterrestrial 3He/4He and 20Ne/22Ne ratios, along with some contaminant terrestrial atmospheric gases. A mixture of solar and Earth's atmospheric gas is the best explanation for the container gas composition. Fragmentation of Ryugu grains within the sample container is discussed on the basis of the estimated amount of indigenous He and the size distribution of the recovered Ryugu grains. This is the first successful return of gas species from a near-Earth asteroid.

Time-series variations in 129I concentrations and 129I/137Cs ratios in suspended particulate matter collected in eastern Japan immediately after the 2011 nuclear accident in Fukushima, Japan.

We have determined the hourly atmospheric concentrations of 129I in aerosols dispersed into the atmosphere by the nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FD1NPP) on March 11, 2011. Data were obtained by measuring the quantity of 129I in suspended particulate matter (SPM) collected on filter tapes at 41 SPM monitoring stations in Fukushima and other prefectures in eastern Japan, including the metropolitan area of Tokyo and the surrounding area. After scrutiny, 500 out of 920 hourly SPM samples were determined to be reliable (i.e., devoid of cross-contamination), and these were subjected to further analysis and discussion. Based on the data from these samples, especially data from the four SPM sampling sites located close to the FD1NPP (Futaba, Naraha, Haramachi and Nihonmatsu), the time-series variations in the atmospheric concentration of 129I and the activity ratio of 129I/137Cs were reconstructed by using 137Cs concentration data in the literature. 129I and 137Cs were observed to be continuously and sometimes explosively dispersed into the atmosphere in aerosols transported by radioactive plumes from the FD1NPP. The highest activity concentrations of 129I and 137Cs were observed in the SPM sample at the Futaba SPM station (3.2 km west-northwest of the FD1NPP) at 14:00-15:00 on March 12 after the venting of Unit 1. Systematically high 129I/137Cs activity ratios were observed at the Futaba and Haramachi stations from March 12 to 14, suggesting that radioactive masses released from the FD1NPP during the first few days after the nuclear accident were relatively enriched in radioiodine. High activity ratios of 129I/137Cs were also measured starting on March 21 at Naraha (17.5 km south of FD1NPP) and from March 22-23 in the metropolitan area which must have been caused by a different type of emission event(s) on those days at the FD1NPP, as previously reported. The 129I data from this study are highly effective in the validation and elaboration of the modelling of the atmospheric dispersion of radioiodine. They further contribute to assessing the internal exposure due to inhalation of 131I estimated by means of such elaborate atmospheric diffusion models.

Nondestructive Quantitative Analysis of Difficult-to-Measure Radionuclides 107Pd and 99Tc.

Considering the expanding demand for nuclear waste management of the spent nuclear fuel materials in near future, a nondestructive analytical scheme applicable to one of the most difficult-to-measure nuclides 107Pd, which emits no decay γ-rays and whose half-life is too long to be decayed out during a human lifetime, was designed. The scheme consists of a sophisticated instrument capable of the detection of γ-rays by Ge detectors coupled with time-of-flight measurement of neutrons and a high-intensity pulsed neutron beam and can simultaneously perform time-of-flight-coupled prompt γ-ray analysis (TOF-PGA) as well as PGA and neutron resonance capture analysis (NRCA). The analytical capability for simulated samples of the Tc-platinum group metals (Tc-PGMs) obtained by the group-partitioning process of spent nuclear fuels, which contain not only 107Pd but also 99Tc and other difficult-to-measure fission products, was evaluated. It was confirmed that although PGA and NRCA can accurately analyze both nuclides in individual, single substances, only TOF-PGA can analyze 107Pd as well as 99Tc in the Tc-PGM-simulated sample. The TOF-PGA measurement technique can be widely used for the nondestructive analysis of 107Pd and 99Tc in nuclear wastes.

Reassessment of early 131I inhalation doses by the Fukushima nuclear accident based on atmospheric 137Cs and 131I/137Cs observation data and multi-ensemble of atmospheric transport and deposition models.

The Fukushima Dai-ichi Nuclear Power Plant accidents following the March 11, 2011 Tohoku earthquake, and subsequent tsunami released radioactive materials into the atmosphere and caused significant public health concerns, particularly thyroid cancers in children. However, the lack of measurement data for atmospheric concentrations of 131I has caused persistent and widespread uncertainty. This study estimated the maximum potential thyroid doses of inhaled 131I in the early post-accident phase between March 12 and 23, 2011 by using the hourly measured data of the 137Cs concentrations at 101 suspended particulate matter (SPM) monitoring sites, a new multi-model ensemble (MME) method of simulating 137Cs concentrations using two Atmospheric Transport and Deposition Models (ATDMs), the 131I/137Cs ratio obtained from measurement data analysis, and the internal exposure model. Based on the measurements, the maximum potential thyroid doses were estimated at 3.1-160 mSv at 5 sites in the Fukushima-Hamadori area for 1-year-old children assumed to remain outdoors, whereas they were less than 4.3 mSv at the other sites in the base case of the 131I/137Cs ratio. The spatial distribution of the maximum potential of early inhalation doses was estimated by using the MME and measurements. The inhalation thyroid doses in the evacuation scenarios were compared to the estimates reported by previous studies. The results of the present study were almost congruent with the outcomes of previous investigations except for thyroid doses contributed by highly contaminated plumes on March 12 and 15. The sensitivity analysis for the 131I/137Cs ratio indicated that these plumes carried the potential to significantly increase the thyroid doses of residents.

Determination of trace rare earth elements in rock samples including meteorites by ICP-MS coupled with isotope dilution and comparison methods.

Combining isotope dilution mass spectrometry with a calibration method and choosing appropriate internal standard elements, 14 lanthanides (rare earth elements, REEs) were precisely and accurately determined for rock samples by using quadruple ICP-MS instruments. An enriched spike of 149Sm was used to determine Sm content by an isotope dilution method. Simultaneously, Sm content was determined by a calibration method and the ratio of the two Sm values was used for correcting the preparation loss of the other REEs, which were analyzed only by a calibration method. Indium and Tl were chosen for use as internal standard elements. Applying the procedure developed in this study to the homogenized Allende meteorite powder sample prepared by the Smithsonian Institution, Washington, D. C., US and several geological reference samples issued by the Geological Survey of Japan and the US geological Survey, precision and accuracy of the data obtained were evaluated and the accuracy was found to be equivalent to isotope dilution values obtained by thermal ionization mass spectrometry. Rare earth element concentrations in several meteorite samples were determined, and results indicate that our procedure is appropriate for a wide variety of whole rock compositions.

A new approach for reconstructing the 131I-spreading due to the 2011 Fukushima nuclear accident by means of measuring 129I in airborne particulate matter.

To retrieve the diffusion trajectory of the 131I dispersed in the environment by the nuclear power plant accident in Fukushima in 2011, airborne particulate matter (APM) samples collected in the Tokyo metropolitan area were analyzed for their 129I contents by means of accelerator mass spectrometry. In evaluating blank levels of chemicals and filters used for collecting APM, we established the analytical procedure for determining the 129I activity of as low as 10-8 Bq for a small piece of filter samples (about 0.1 cm2). Coupled with 131I data determined just after the accident, activity ratios of 129I/131I were obtained with a mean value of 2.29 × 10-8 (±28% of a standard deviation). This value is systematically smaller than a mean value of soil samples by 16-24% and the inventory data by 27%, suggesting that 129I was partly lost from APM. As 129I can be a proxy of 131I for APM, it is possible to trace how 131I in the particulate phase spread in eastern Japan and, furthermore, evaluate the internal radiation exposure due to 131I by inhalation of 131I-containing airborne particulates.

Quality of life and functional status of terminally ill head and neck cancer patients: a nation-wide, prospective observational study at tertiary cancer centers in Japan.

BACKGROUND: Little is known about quality of life and functional status of patients with terminally ill head and neck cancers. METHODS: We conducted a multicenter, prospective, observational study to examine quality of life and functional status in terminally ill head and neck cancer patients. RESULTS: Of the 100 patients meeting inclusion criteria, 72 were observed until death. There was no significant difference in the quality of life score between baseline and Week 3. Forty patients (54.9%) could speak and 22 patients (30.5%) could have oral intake upon study entry. Fifty-three patients (74.6%) received enteral nutrition. Twenty-six patients (36.6%) required dressing changes for fungating tumors. The route of nutritional intake (nasogastric tube vs. percutaneous gastric tube) might be predictive for the duration of hospital stay (64 vs. 21 days, P = 0.0372). CONCLUSION: There was no significant relationship between quality of life and functional status seen in this study. Feeding tube type could have the most impact on quality of life.

Inverse modeling of the 137Cs source term of the Fukushima Dai-ichi Nuclear Power Plant accident constrained by a deposition map monitored by aircraft.

The amount of 137Cs released by the Fukushima Dai-ichi Nuclear Power Plant accident of 11 March 2011 was inversely estimated by integrating an atmospheric dispersion model, an a priori source term, and map of deposition recorded by aircraft. An a posteriori source term refined finer (hourly) variations comparing with the a priori term, and estimated 137Cs released 11 March to 2 April to be 8.12 PBq. Although time series of the a posteriori source term was generally similar to those of the a priori source term, notable modifications were found in the periods when the a posteriori source term was well-constrained by the observations. Spatial pattern of 137Cs deposition with the a posteriori source term showed better agreement with the 137Cs deposition monitored by aircraft. The a posteriori source term increased 137Cs deposition in the Naka-dori region (the central part of Fukushima Prefecture) by 32.9%, and considerably improved the underestimated a priori 137Cs deposition. Observed values of deposition measured at 16 stations and surface atmospheric concentrations collected on a filter tape of suspended particulate matter were used for validation of the a posteriori results. A great improvement was found in surface atmospheric concentration on 15 March; the a posteriori source term reduced root mean square error, normalized mean error, and normalized mean bias by 13.4, 22.3, and 92.0% for the hourly values, respectively. However, limited improvements were observed in some periods and areas due to the difficulty in simulating accurate wind fields and the lack of the observational constraints.

Synergistic effect of combining two nondestructive analytical methods for multielemental analysis.

We developed a new analytical technique that combines prompt gamma-ray analysis (PGA) and time-of-flight elemental analysis (TOF) by using an intense pulsed neutron beam at the Japan Proton Accelerator Research Complex. It allows us to obtain the results from both methods at the same time. Moreover, it can be used to quantify elemental concentrations in the sample, to which neither of these methods can be applied independently, if a new analytical spectrum (TOF-PGA) is used. To assess the effectiveness of the developed method, a mixed sample of Ag, Au, Cd, Co, and Ta, and the Gibeon meteorite were analyzed. The analytical capabilities were compared based on the gamma-ray peak selectivity and signal-to-noise ratios. TOF-PGA method showed high merits, although the capability may differ based on the target and coexisting elements.

First retrieval of hourly atmospheric radionuclides just after the Fukushima accident by analyzing filter-tapes of operational air pollution monitoring stations.

No observed data have been found in the Fukushima Prefecture (FP) for the time-series of atmospheric radionuclides concentrations just after the Fukushima Daiichi Nuclear Power Plant (FD1NPP) accident. Accordingly, current estimates of internal radiation doses from inhalation, and atmospheric radionuclide concentrations by atmospheric transport models are highly uncertain. Here, we present a new method for retrieving the hourly atmospheric (137)Cs concentrations by measuring the radioactivity of suspended particulate matter (SPM) collected on filter tapes in SPM monitors which were operated even after the accident. This new dataset focused on the period of March 12-23, 2011 just after the accident, when massive radioactive materials were released from the FD1NPP to the atmosphere. Overall, 40 sites of the more than 400 sites in the air quality monitoring stations in eastern Japan were studied. For the first time, we show the spatio-temporal variation of atmospheric (137)Cs concentrations in the FP and the Tokyo Metropolitan Area (TMA) located more than 170 km southwest of the FD1NPP. The comprehensive dataset revealed how the polluted air masses were transported to the FP and TMA, and can be used to re-evaluate internal exposure, time-series radionuclides release rates, and atmospheric transport models.

Quality assessment of INAA data for small-sized environmental reference samples.

Instrumental neutron activation analysis (INAA) was applied for the accurate and precise determination of minor and trace elements in small-sized aliquants (1 to 2 mg) of two certified reference materials (CRM), NIES No. 8 and NIST 1632c. Four laboratories used either comparative- or k0-INAA, or both, and repeated the analysis more than ten times for each CRM. Based on z-scores and zeta scores of analytical data, QA/QC in analyzing such small scale of the two reference samples was assessed, revealing that there was a clear difference in the analytical ability among participating laboratories. It was concluded that the two CRM samples on the mg scale can be used as reference samples in INAA of a similarly small-scaled sample, at least for the 16-18 elements examined.

[Frequency and distributions of cervical lymph node metastases in oropharyngeal squamous cell carcinoma].

OBJECTIVES: To examine the frequency and distribution of cervical lymph node metastases in oropharyngeal squamous cell carcinoma (SCC) and the necessities of prophylactic treatment of the neck. METHODOLOGY: We conducted a retrospective study of 242 patients with SCC of the oropharynx treated by surgery as the initial therapy at the National Cancer Center East Hospital from 1994 to 2008, excluding 53 patients who had local recurrences and 9 patients who had previously undergone neck dissection for metastasis from an unknown primary. We defined "potential lymph node metastases" as cases pathologically positive for lymph node metastases and/or secondary lymph node metastases and analyzed the necessity of prophylactic neck dissection for cases clinically negative for cervical metastases. RESULTS: One hundred and eighty patients (148 males, 32 females) were included. The median age was 62 years (35 to 78). The clinical stages were Stage I in 20 patients, Stage II in 36 patients, Stage III in 39 patients, and Stage IV in 85 patients. In the ipsilateral neck of 70 patients at clinical stage N0, 15 patients (21.4%) were positive for potential lymph node metastases. There was no significant difference in the frequency of metastases by subsite. In terms of T classification, the positivity rates were 5.0% in patients at T1, 19.4% at T2, 44.4% at T3, and 60.0% at T4. In the contralateral neck of 70 patients at clinical stage N0, only 2 patients (2.9%) were positive for potential lymph node metastases. In the contralateral neck of 93 patients at clinical stage N1, N2a, or N2b (i.e., unilateral lymph node swelling), 16 patients (17.2%) were positive for potential lymph node metastases. The positivity rates by subsite were higher in patients with anterior, superior and posterior wall cancer than those with lateral wall cancer. CONCLUSIONS: In the ipsilateral neck of patients at clinical stage N0, prophylactic neck dissection is not necessary for patients at T1 but necessary for those at T3 or T4. In the contralateral neck of such patients, prophylactic neck dissection is not recommended. In the contralateral neck of patients with unilateral lymph node swelling, prophylactic neck dissection is recommended for patients with anterior, superior or posterior wall cancer.

The effectiveness of chemoradiation therapy and salvage surgery for hypopharyngeal squamous cell carcinoma.

OBJECTIVE: The objective of this study was to evaluate the results of salvage surgery after definitive chemoradiation for hypopharyngeal squamous cell carcinoma. METHODS: This was a retrospective cohort study. Of the 79 patients with previously untreated hypopharyngeal squamous cell carcinoma who received definitive chemoradiation from January 2004 to January 2009, 24 who had recurrence and underwent salvage surgery at the National Cancer Center Hospital East, Chiba, Japan, were enrolled in this study. RESULTS: Of the 24 patients who underwent salvage surgery with curative intent, 13 had an isolated local failure, eight had an isolated neck failure and three had combined local and regional failure. Postoperative surgical complications were observed in eight (33.3%) patients. Of the 24 patients undergoing salvage surgery, 12 (50%) had recurrence. In 11 of these patients, death ensued from salvage failure, defined as the presence of any recurrence after salvage treatment. The causes of cancer-specific death ensuing from salvage failure were regional recurrence of the tumor (n = 6) (one of whom had concurrent distant metastases) and distant metastases alone (n = 5). No local recurrence after salvage surgery was observed in our group of patients. The disease-free and overall 24-month survival rates were 49.0 and 50.0%, respectively. Those patients who initially presented with unresectable disease had lower overall survival compared with those who initially presented with resectable disease (P = 0.0003). CONCLUSIONS: The oncologic outcomes were acceptable in those patients in whom salvage surgery was carried out. Those who initially presented with unresectable disease had a poor prognosis.

Accurate determination of trace amounts of phosphorus in geological samples by inductively coupled plasma atomic emission spectrometry with ion-exchange separation.

In order to determine trace amounts of phosphorus in geological and cosmochemical rock samples, simple as well as reliable analytical schemes using an ICP-AES instrument were investigated. A (conventional) ICP-AES procedure could determine phosphorus contents at the level of several 100 µg g(-1) with a reasonable reproducibility (<10% for 200 µg g(-1); 1σ). An ICP-AES procedure coupled with matrix-separation using cation and anion exchange resins could lower the quantification level down to 1 µg g(-1) or even lower under the present experimental conditions. The matrix-separation ICP-AES procedure developed in this study was applied to twenty-one geological reference samples issued by Geological Survey of Japan. Obtained values vary from 1250 µg g(-1) for JB-3 (basalt) to 2.07 µg g(-1) for JCt-1 (carbonate). Matrix-separation ICP-AES yielded reasonable reproducibility (less than 8.3%; 1σ) of three replicate analyses for all the samples analyzed. In comparison of our data with certificate values as well as literature or reported values, there appear to be an apparent (and large) discrepancy between our values and certificate/reported values regardless of phosphorus contents. Based on the reproducibility of our data and the analytical capability of the matrix-separation ICP-AES procedure developed in this study (in terms of quantification limit, recovery, selectivity of an analyte through pre-concentration process, etc.), it is concluded that certified values for several reference standard rocks should be reevaluated and revised accordingly. It may be further pointed that some phosphorus data reported in literatures should be critically evaluated when they are to be referred in later publications.

Accurate determination of chlorine, bromine, and iodine in sedimentary rock reference samples by radiochemical neutron activation analysis and a detailed comparison with inductively coupled plasma mass spectrometry literature data.

Trace amounts of three halogens (chlorine, bromine, and iodine) were determined using radiochemical neutron activation analysis (RNAA) for nine sedimentary rocks and three rhyolite samples. To obtain high-quality analytical data, the radiochemical procedure of RNAA was improved by lowering the background in gamma-ray spectrometry and completing the chemical procedure more rapidly than in conventional procedures. A comparison of the RNAA data of Br and I with corresponding inductively coupled plasma mass spectrometry (ICPMS) literature data revealed that the values obtained by ICPMS coupled with pyrohydrolysis preconcentration were systematically lower than the RNAA data for some reference samples, suggesting that the quantitative collection of Br and I cannot always be achieved by the pyrohydrolysis for some solid samples. The RNAA data of three halogens can classify sedimentary rock reference samples into two groups (the samples from inland water and those from seawater), implying the geochemical significance of halogen data.

Observation as an option for epithelial positive margin after partial glossectomy in stage I and II squamous cell carcinoma: analysis of 365 cases.

OBJECTIVE: This study was conducted to assess local recurrence and clinical prognosis in patients diagnosed as having a positive margin in the epithelial layer after a partial glossectomy treated by close observation. METHODS: A total of 365 cases of squamous cell carcinoma of the tongue diagnosed as clinical Stage I or II, treated by partial glossectomy in the National Cancer Center Hospital East between 1992 and 2006, were studied retrospectively. RESULTS: Pathological findings showed that 13 cases had positive margins in the epithelial layer, 4 (30.8%) of whom showed up with local recurrence in 4.4 years (3.0-5.0) on average. Lymph node recurrence was not observed and the 5-year overall survival rate was 76.2% in those 13 cases. The treatment for the recurrent cases was an additional partial glossectomy without neck dissection, which resulted in no recurrence and a survival rate of 100% after an average follow-up of 6.7 years. CONCLUSIONS: We suggest careful observation as one option for cases diagnosed with epithelial positive margin.

Mucosal defect repair with a polyglycolic acid sheet.

OBJECTIVE: Early-stage oral or oropharyngeal carcinomas are often treated with surgical resection. Resulting wounds that are too large for primary closure can be covered with skin grafts or patches made from various biomaterials. Recently, polyglycolic acid sheets have been used for this purpose. METHODS: We treated six patients with large wounds resulting from the resection of oral or oropharyngeal squamous cell carcinoma by grafting polyglycolic acid sheet patches. All patients were initially treated at the National Cancer Center East Hospital from March 2010 through July 2012. After mucosal resection, the wounds were covered with polyglycolic acid sheet patches attached with fibrin glue. Oral intake was started 4 days after surgery. RESULTS: Mucosal resection was the initial treatment in seven patients (five with oral squamous cell carcinoma and two with oropharyngeal squamous cell carcinoma). The polyglycolic acid sheet patches became detached in two patients (on the day of surgery and on postoperative day 6), who then required large doses of analgesics. A patient who underwent tooth extraction also required large doses of analgesics. The other four patients required only small doses of analgesics. One patient had bleeding at the surgical site. No adverse effects were caused by the polyglycolic acid sheet patch or by fibrin glue. CONCLUSIONS: Our study has shown that grafting of a polyglycolic acid sheet patch is effective and provides good pain control for patients with large, open wounds after mucosal resection of oral or oropharyngeal squamous cell carcinoma. We plan to evaluate tissue contraction and oral intake after polyglycolic acid patch grafting.

Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic.

The 34-million-year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., end-Triassic extinction event), but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits. Here, we report evidence for an impact event (platinum group elements anomaly with nickel-rich magnetite and microspherules) from the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridium-enriched ejecta layers of the Late Triassic may be found on a global scale. The ejecta deposit is constrained by microfossils that suggest correlation with the 215.5-Mya, 100-km-wide Manicouagan impact crater in Canada. Our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine planktons. However, such an event has been reported among marine faunas and terrestrial tetrapods and floras in North America. We, therefore, suggest that the Manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm.