A globally fragmented and mobile lithosphere on Venus.

Venus has been thought to possess a globally continuous lithosphere, in contrast to the mosaic of mobile tectonic plates that characterizes Earth. However, the Venus surface has been extensively deformed, and convection of the underlying mantle, possibly acting in concert with a low-strength lower crust, has been suggested as a source of some surface horizontal strains. The extent of surface mobility on Venus driven by mantle convection, however, and the style and scale of its tectonic expression have been unclear. We report a globally distributed set of crustal blocks in the Venus lowlands that show evidence for having rotated and/or moved laterally relative to one another, akin to jostling pack ice. At least some of this deformation on Venus postdates the emplacement of the locally youngest plains materials. Lithospheric stresses calculated from interior viscous flow models consistent with long-wavelength gravity and topography are sufficient to drive brittle failure in the upper Venus crust in all areas where these blocks are present, confirming that interior convective motion can provide a mechanism for driving deformation at the surface. The limited but widespread lithospheric mobility of Venus, in marked contrast to the tectonic styles indicative of a static lithosphere on Mercury, the Moon, and Mars, may offer parallels to interior-surface coupling on the early Earth, when global heat flux was substantially higher, and the lithosphere generally thinner, than today.

Measuring stigma associated with hepatitis B virus infection in Sierra Leone: Validation of an abridged Berger HIV stigma scale.

Stigma associated with hepatitis B virus (HBV) is common in endemic countries; however; instruments are lacking to accurately measure HBV-related stigma. We therefore aimed to develop and validate a concise instrument for measuring perceived HBV-related stigma in Sierra Leone. We enrolled 220 people living with HBV (PWHB) aged ≥18 years from August to November 2022. The initial Likert-scale instrument entailed 12 items adapted from Berger's HIV Stigma Scale. We included four additional items adapted from the USAID indicators for enacted stigma. The proposed scale's psychometric properties were assessed. After item reduction, the final HBV Stigma Scale consisted of 10 items and had good internal consistency (overall Cronbach's α = 0.74), discriminant, and construct validity. Exploratory factor analysis produced a three-dimensional structure accounting for 59.3% of variance: personalized stigma driven by public attitudes (six items), negative self-image (two items), and disclosure concerns (two items). Overall, 72.8% of respondents reported perceived HBV-related stigma (mean score 29.11 ± 4.14) and a similar proportion (73.6%) reported at least one instance of enacted stigma. In assessing criterion-related validity, perceived HBV-related stigma correlated strongly with enacted stigma (r = 0.556) and inversely with having family/friends with HBV (r = -0.059). The 10-item HBV Stigma Scale demonstrated good internal consistency and validity and is suitable for screening for HBV-related stigma in Sierra Leone. The psychometric properties of the scale can be optimized with item additions/modifications and confirmatory factor analysis. The scale may help in combating stigma as a barrier to achieving HBV global elimination goals.

Determinants of incomplete childhood hepatitis B vaccination in Sierra Leone, Liberia, and Guinea: Analysis of national surveys (2018-2020).

Vaccination against hepatitis B virus (HBV) is effective at preventing vertical transmission. Sierra Leone, Liberia, and Guinea are hyperendemic West African countries; yet, childhood vaccination coverage is suboptimal, and the determinants of incomplete vaccination are poorly understood. We analyzed national survey data (2018-2020) of children aged 4-35 months to assess complete HBV vaccination (receiving 3 doses of the pentavalent vaccine) and incomplete vaccination (receiving <3 doses). Statistical analysis was conducted using the complex sample command in SPSS (version 28). Multivariate logistic regression was used to identify determinants of incomplete immunization. Overall, 11,181 mothers were analyzed (4,846 from Sierra Leone, 2,788 from Liberia, and 3,547 from Guinea). Sierra Leone had the highest HBV childhood vaccination coverage (70.3%), followed by Liberia (64.6%) and Guinea (39.3%). Within countries, HBV vaccination coverage varied by socioeconomic characteristics and healthcare access. In multivariate regression analysis, factors that were significantly associated with incomplete vaccination in at least one country included sex of the child, Muslim mothers, lower household wealth index, <4 antenatal visits, home delivery, and distance to health facility vaccination (all p < 0.05). Understanding and addressing modifiable determinants of incomplete vaccination will be essential to help achieve the 2030 viral hepatitis elimination goals.

Mercury's Crustal Thickness and Contractional Strain.

The crust of Mercury has experienced contraction on a global scale. Contractional deformation is expressed by a broadly distributed network of lobate thrust fault scarps. The most likely principal source of stress is global contraction from cooling of Mercury's interior. Global contraction alone would be expected to result in a uniformly distributed population of thrust faults. Mercury's fault scarps, however, often occur in long, linear clusters or bands. An analysis of the contractional strain as a function of crustal thickness, estimated in two crustal thickness models (CT1 and CT2) derived from gravity and topography data obtained during the MESSENGER mission, indicates the greatest contractional strain occurs in crust 50-60 km thick. On Earth, mantle downwelling can thicken and compress overlying crust, regionally concentrating thrust faults. Clusters of lobate scarps collocated with regions of thick crust suggest downward mantle flow contributed to the localization of lithosphere-penetrating thrust faults.

Awareness, use, attitude and perceived need for Complementary and Alternative Medicine (CAM) education among undergraduate pharmacy students in Sierra Leone: a descriptive cross-sectional survey.

BACKGROUND: The widespread use of CAM around the world requires health professionals including pharmacists to have the required knowledge to better advise their patients. This has lead to an increased need for the inclusion of CAM instruction into the mainstream undergraduate Pharmacy education. This study was designed to describe pharmacy students awareness, use, attitude and perceived need for CAM education at COMAHS-USL and at the same time, determine how these descriptive outcomes are influenced by the socio-demographic variables considered in this study. METHODS: A descriptive cross-sectional survey was conducted among undergraduate pharmacy students (n = 90) at the College of Medicine and Allied Health Sciences, University of Sierra Leone using a structured questionnaire. Chi square, fisher exact test, and general linear model univariate analysis were used to compare data between independent cohorts. RESULTS: All 90 (100%) of the students were aware and have used (except Ayurveda) at least one of the listed CAM modalities. Herbal/Botanical/Supplements followed by Spirituality/Prayer were the most commonly known and used CAM modalities. Almost two thirds of students considered the CAM modalities they have used to be effective and not harmful. Overall, pharmacy students had a positive attitude towards CAM (Mean attitudinal score = 34.9 ± 4. 5 (range 19-43)) with fourth and fifth year students showing a significantly less positive attitude as compared to the first, second and third year (B = -3.203 p = 0.001, 95% confidence interval -5.093 to -1.314). The media [53 (58.9%)] was the most frequent source of information about CAM. Nearly all students [89 (98.9%)] agreed that CAM knowledge is important to them as future pharmacist and that CAM should be included into the Pharmacy curriculum at COMAHS-USL [81 (90.0%)]. CONCLUSION: Pharmacy students in Sierra Leone are aware of and have used at least one of the CAM modalities and do show a positive attitude towards CAM. This was demonstrated by their overwhelming endorsement for CAM course to be part of the undergraduate pharmacy training at COMAHS-USL. This study among others will inform and guide the development and implementation of CAM instruction at COMAHS-USL.

Current tobacco use and susceptibility to using tobacco among non-users of tobacco: A cross-sectional study among school-going adolescents in Sierra Leone.

INTRODUCTION: Tobacco use is a global health threat associated with a high disease burden and death. Current tobacco use and susceptibility to using tobacco products among adolescents who are potential adult tobacco users have not been explored in Sierra Leone. Thus, we aimed to estimate the prevalence and correlates of current tobacco use and tobacco non-users susceptibility to using tobacco amongst high school students in Sierra Leone. METHODS: We used data obtained from the 2017 Sierra Leone Global Youth Tobacco Survey (GYTS), which presented information collected from 6680 students aged 11-17 years nationwide. Gender-based correlates of current use and susceptibility to using tobacco among non-tobacco users were determined by complex sample logistic regression analyses. Adjusted odds ratios (AOR) and respective 95% confidence intervals (CIs) are reported. A p<0.05 was considered significant. RESULTS: The prevalence of current tobacco use among high school adolescents in Sierra Leone was 24.6%, higher in males (27.9%) than in females (18.6%). Male (AOR=1.50; 95% CI: 1.18-1.91), parental smoking (AOR=1.73; 95% CI: 1.32-2.26) exposure to household secondhand smoke (AOR=1.82; 95% CI: 1.27-2.62), having peers who smoke (AOR=2.24; 95% CI: 1.51-3.31) were more likely to be currently using tobacco. The overall tobacco non-users susceptibility to using tobacco among adolescents in Sierra Leone was 18.2% (males 18.0%, females 18.5%). Exposure to tobacco promotion (AOR=1.50; 95% CI: 1.06-2.10) and non-exposure to anti-smoking education (AOR=1.39; 95% CI: 1.05-1.86) were significantly associated with tobacco non-users' susceptibility to using tobacco. CONCLUSIONS: Our study suggests that one in four school-going adolescents currently uses tobacco, with nearly one in five non-users susceptible to using tobacco. Given the high prevalence of tobacco product use among adults in Sierra Leone, our findings highlight the need for policies and interventions to prevent tobacco use behavior among adolescents, aimed at averting tobacco use in adulthood.

Measuring Stigma Associated with Hepatitis B Virus Infection in Sierra Leone: Validation of an Abridged Berger HIV Stigma Scale.

Stigma associated with hepatitis B virus (HBV) is common in endemic countries; however; instruments are lacking to accurately measure HBV-related stigma. We therefore aimed to develop and validate a concise instrument for measuring perceived HBV-related stigma in Sierra Leone. We enrolled 220 people living with HBV (PWHB) aged ≥ 18 years from August to November 2022. The initial Likert-scale instrument entailed 12 items adapted from Berger's HIV Stigma Scale. We included 4 additional items adapted from the USAID indicators for enacted stigma. The proposed scale's psychometric properties were assessed. After item reduction, the final HBV Stigma Scale consisted of 10 items and had good internal consistency (overall Cronbach's α = 0.74), discriminant and construct validity. Exploratory factor analysis produced a 3-dimensional structure accounting for 59.3% of variance: personalized stigma driven by public attitudes (6 items), negative self-image (2 items), and disclosure concerns (2 items). Overall, 72.8% of respondents reported perceived HBV stigma (mean score 29.11 ± 4.14) and a similar a proportion (73.6%) reported at least one instance of enacted stigma. In assessing criterion-related validity, perceived HBV-related stigma correlated strongly with enacted stigma (r = 0.556) and inversely with having family/friends with HBV (r = -0.059). The 10-item HBV Stigma Scale demonstrated good internal consistency and validity and is suitable for screening for HBV-related stigma in Sierra Leone. The psychometric properties of the scale can be optimized with item additions/modifications and confirmatory factor analysis. The scale may help in combating stigma as a barrier to achieving HBV global elimination goals.

Perceived and Enacted HIV-Related Stigma in Eastern and Southern Sierra Leone: A Psychometric Study of an HIV Stigma Scale.

Background: HIV stigma continues to hinder the care of people with HIV (PWH), especially in low-resource settings. We aimed to adapt and validate a concise HIV stigma scale for perceived HIV stigma in Sierra Leone. Methods: We enrolled participants in two HIV clinics in Eastern and Southern Sierra Leone in 2022. We assessed perceived stigma using a 12-item adaptation of Berger's HIV Stigma Scale and enacted stigma using select USAID indicators. We used ordinal logistic regression to identify predictors of perceived stigma and Pearson's correlation to examine associations between perceived and enacted stigma. Results: 624 PWH were enrolled. The final adapted 6-item HIV stigma scale demonstrated acceptable internal consistency (Cronbach's α = 0.72) and a four-factor solution accounting for 84.8% of variance: concern about public attitude (2 items), personalized stigma (2 items), negative self-image (1 item), and disclosure concerns (1 item). The prevalence of perceived HIV stigma was 68.6%, with disclosure concerns as the most prominent contributor. Enacted HIV stigma was reported by only 6.7% of participants, with partner/spousal abandonment and workplace stigma being the most common discriminatory experiences. Employment (ß = 0.525, p <0.001), residence in Eastern Sierra Leone (ß = 3.215, p < 0.001), and experiencing enacted stigma (ß = 0.804, p < 0.001) were significantly associated with perceived stigma. Having a family member or friend with HIV (ß = -0.499, p < 0.001), and HIV disclosure (ß = -0.710, p < 0.001) were protective against perceived stigma. Enacted stigma strongly correlated with partner abandonment and family isolation (r = 0.223, p < 0.001). Conclusion: We found high levels of perceived HIV stigma, underscoring the need for targeted interventions to combat stigma and promote inclusivity for PWH in Sierra Leone.

Assessment of Knowledge, Stigmatizing Attitudes and Health-Seeking Behaviors Regarding Hepatitis B Virus Infection in a Pharmacy and Community Setting in Sierra Leone: A Cross-Sectional Study.

Hepatitis B virus (HBV) is a major global health challenge. Emerging evidence suggests that poor knowledge and stigma are impacting HBV control efforts in sub-Saharan Africa (SSA), but their role is not well understood. We conducted a cross-sectional study of adults aged ≥18 years in a community and pharmacy setting in Freetown, Sierra Leone. A structured questionnaire was used to assess knowledge, stigmatizing attitudes and health-seeking behaviors regarding HBV. Logistic regression was used to identify predictors of HBV knowledge and related stigma. A total of 306 adult participants were enrolled (50.7% male, 7.5% HBV positive and 11.7% vaccinated). Overall, 52.2% had good HBV knowledge and 49.3% expressed a stigmatizing attitude towards people with HBV. Notwithstanding, 72.2% stated they would receive the HBV vaccine if offered, 80.4% would take anti-HBV medication and 78.8% would be willing to attend clinic regularly. Good HBV knowledge was associated with HBV positive status (aOR 4.41; p = 0.029) and being vaccinated against HBV (aOR 3.30; p = 0.034). HBV-related stigma was associated with secondary or higher level of education (aOR 2.36; p < 0.001), good HBV knowledge (aOR 2.05; p = 0.006) and pharmacy setting (aOR 1.74, p = 0.037). These findings suggest that education and stigma reduction may benefit HBV elimination efforts in SSA.

Impact of COVID-19 on hepatitis B screening in Sierra Leone: insights from a community pharmacy model of care.

Objectives: To assess the impact of COVID-19-related interruptions and seasonal patterns on hepatitis B virus (HBV) screening in a hyperendemic setting in Sierra Leone. Methods: We conducted a retrospective study of HBV testing in a community pharmacy in Freetown, Sierra Leone, from October 01, 2019, through September 30, 2022. We compared participant characteristics using Pearson's chi-square test. We evaluated trends in HBV screening and diagnosis using one-way analysis of variance with Tukey's or Dunnett's post-test. Results: Of 920 individuals screened, 161 had detectable HBV surface antigen (seroprevalence 17.5% [95% CI 14.9-20.4]). There was a 100% decrease in HBV screening during January-June of 2020; however, screening increased by 27% and 23% in the first and second years after COVID-19, respectively. Mean quarterly tests showed a significant upward trend: 55 ± 6 tests during January-March (baseline), 74 ± 16 tests during April-June, 101 ± 3 tests during July-September, and 107 ± 17 tests during October-December (one-way analysis of variance test for trend, F = 7.7, P = 0.0254) but not the mean quarterly number of people diagnosed with HBV (F = 0.34, P = 0.7992). Conclusion: Community-based HBV screening dramatically improved following temporary disruptions related to COVID-19. Seasonal variation in HBV screening, but not HBV diagnosis, may have implications for HBV elimination efforts in Sierra Leone and other West African countries.

Understanding COVID-19 Vaccine Uptake and Hesitancy among People with HIV in Freetown, Sierra Leone: A Cross-Sectional Study.

People with HIV (PWH) incur a higher risk of COVID-19-related morbidity and mortality rates, yet less is known about COVID-19 vaccine uptake and hesitancy in this group. We conducted a cross-sectional study in Freetown, Sierra Leone, from April to June 2022, using the VAX scale, a validated instrument, to assess attitudes towards COVID-19 vaccination and calculate the hesitancy (VAX) scores. We used generalized linear models to identify the factors associated with vaccine hesitancy. Overall, 490 PWH were enrolled (71.4% female, median age: 38 years, median CD4 count: 412 cells/mm3). About 17.3% received ≥1 dose of a COVID-19 vaccine. The mean VAX score was 43.14 ± 7.05, corresponding to 59.9% participants being vaccine-hesitant. A preference for natural immunity (65.8%) and concerns about profiteering (64.4%) were the commonest reasons for hesitancy, followed by a mistrust of vaccine benefits (61.4%) and worries about future effects (48.0%). In the adjusted regression analysis, being a Muslim (ß = 2.563, p < 0.001) and having an urban residence (ß = 1.709, p = 0.010) were associated with greater vaccine hesitancy, while testing for COVID-19 was associated with reduced vaccine hesitancy (ß = -3.417, p = 0.027). These findings underscore the importance of addressing vaccine hesitancy as a critical element boosting COVID-19 vaccine uptake among PWH.

Understanding COVID-19 Vaccine Uptake and Hesitancy Among People With HIV in Freetown, Sierra Leone: A Cross-sectional Study.

Objectives: People living with HIV (PWH) are at increased risk of COVID-19 related morbidity and mortality, yet less is known about COVID-19 vaccination uptake and hesitancy, especially in sub-Saharan Africa. We aimed to evaluate COVID-19 vaccine uptake and hesitancy among PWH in Sierra Leone. Methods: We conducted a cross-sectional study in a convenience sample of PWH in routine care at Connaught Hospital in Freetown, Sierra Leone from April through June 2022. We collected sociodemographic and health-related data. We used the VAX Scale, a validated instrument to assess attitudes towards COVID-19 vaccination. From the responses, we constructed hesitancy (VAX) scores, with higher scores implying negative attitudes towards vaccination. We used generalized linear models to identify factors associated with vaccine hesitancy. Results: A total of 490 PWH were enrolled (71.4% female, median age 38 years, median CD4 count 412 cells/mm3, 83.9% virologically suppressed). About 17.3% had received at least one dose of a COVID-19 vaccine. The mean VAX score was 43.14 ± 7.05, corresponding to 59.9% participants classified as vaccine hesitant. Preference for natural immunity (65.8%) and concerns about commercial profiteering (64.4%) were the commonest reasons for hesitancy, followed by mistrust of vaccine benefits (61.4%) and worries about future side effects (48.0%). In adjusted regression analysis, being Muslim (ß = 2.563, p < 0.001) and residence in urban areas (ß = 1.709, p = 0.010) were associated with greater vaccine hesitancy, while having tested ever for COVID-19 was associated with lesser vaccine hesitancy (ß = -3.417, p = 0.027). Conclusion: We observed a low COVID-19 vaccine uptake and high hesitancy among PWH in Sierra Leone. Our findings underscore the need to address vaccine hesitancy as a critical element of efforts to boost COVID-19 vaccine uptake among this population in Sierra Leone.

Prevalence of Chronic Hepatitis B Virus Infection in Sierra Leone, 1997-2022: A Systematic Review and Meta-Analysis.

Hepatitis B virus (HBV) infection is a major public health problem in Sierra Leone, yet reliable estimates of cases are lacking. This study aimed to provide an estimate of the national prevalence of chronic HBV infection in the general population and select groups in Sierra Leone. We used the electronic databases PubMed/MEDLINE, Embase, Scopus, ScienceDirect, Web of Science, Google Scholar, and African Journals Online to systematically review articles reporting hepatitis B infection surface antigen seroprevalence estimates in Sierra Leone during 1997-2022. We estimated pooled HBV seroprevalence rates and assessed potential sources of heterogeneity. Of 546 publications screened, 22 studies with a total sample size of 107,186 people were included in the systematic review and meta-analysis. The pooled prevalence of chronic HBV infection was 13.0% (95% CI, 10.0-16.0) (I2 = 99%; Pheterogeneity < 0.01). During the study period, the HBV prevalence rates were as follows: 17.9% (95% CI, 6.7-39.8) before 2015, 13.3% (95% CI, 10.4-16.9) during 2015-2019, and 10.7% (95% CI, 7.5-14.9) during 2020-2022. The use of the 2020-2022 HBV prevalence estimates corresponded to 870,000 cases of chronic HBV infection (uncertainty interval, 610,000-1,213,000), or approximately one in nine people. The highest HBV seroprevalence estimates were among adolescents aged 10-17 years (17.0%; 95% CI, 8.8-30.5), Ebola survivors (36.8%; 95% CI, 26.2-48.8), people living with HIV (15.9%; 95% CI, 10.6-23.0), and those in the Northern Province (19.0%; 95% CI, 6.4-44.7) and Southern Province (19.7%; 95% CI, 10.9-32.8) regions. These findings may help inform national HBV program implementation in Sierra Leone.

Factors Associated with HBsAg Seropositivity among Pregnant Women Receiving Antenatal Care at 10 Community Health Centers in Freetown, Sierra Leone: A Cross-Sectional Study.

Hepatitis B (HBV) is a major public health threat in Sierra Leone. Pregnant women are disproportionately impacted, yet little is known about the epidemiology of HBV in this group. We conducted a cross-sectional study of pregnant women aged ≥16 years receiving antenatal care across 10 community health centers in Freetown from July to September 2021 to assess the prevalence and associated factors of HBsAg seropositivity. Logistic regression was used to identify the predictors of HBsAg seropositivity. In total, 394 pregnant women were screened. The mean age was 24.4 ± 4.9 years, 78.2% were married, and 47.2% were in the second trimester. Only 1% had received the HBV vaccine. The prevalence of HBsAg was 7.9%, while HIV was 5.8% and HIV/HBV co-infection was 0.3%. Regarding high-risk practices, 76.6% reported female genital circumcision, 41.9% ear piercing, 29.0% endorsed multiple sexual partners, and 23.6% reported sexually transmitted infections. In the logistic regression analysis, having a husband/partner with HBV (adjusted odds ratio (aOR): 6.54; 95% CI: [1.72-24.86]; p = 0.006) and residing in Central Freetown (aOR: 4.00; 95% CI: [1.46-11.00]; p = 0.007) were independently associated with HBsAg seropositivity. Our findings support the scaling up of HBV services to target pregnant women and their partners for screening and vaccination to help reduce mother-to-child transmission rates in Sierra Leone.

COVID-19 Vaccine Hesitancy among Healthcare Workers and Trainees in Freetown, Sierra Leone: A Cross-Sectional Study.

Despite having safe and efficacious vaccines against COVID-19, vaccine hesitancy is widespread. Although a trusted source of information, vaccine hesitancy has been reported among healthcare professionals, yet few studies have explored this phenomenon in sub-Saharan Africa. We conducted a cross-sectional survey of healthcare professionals in Sierra Leone from January to March 2022. Measures included sociodemographic/health-related information and COVID-19-related concerns. From the responses, we constructed a hesitancy (VAX) score, with higher scores implying negative attitudes or unwillingness to vaccinate. Multivariate linear regression was used to access factors associated with vaccine hesitancy. Overall, 592 participants submitted responses (67.2% female, mean age 29 years, 5.6% physicians/pharmacists, 44.3% medical students, 29.2% nurses, 20.9% nursing students). The mean VAX score was 43.27 ± 8.77, with 60.1% of respondents classified as vaccine hesitant (>50th percentile) and 13.8% as highly hesitant (>75th percentile). Worries about unforeseen future effects (76.3%), a preference for natural immunity (59.5%), and profiteering/mistrust of health authorities (53.1%) were the most common concerns. Being a medical student (ß = 0.105, p = 0.011) and previously refusing a recommended vaccine (ß = 0.177, p < 0.001) were predictors of COVID-19 vaccine hesitancy. Our findings call for addressing vaccine hesitancy among healthcare professionals as an essential component of strategies aimed at increasing COVID-19 vaccine uptake in this setting.

The thickness of radar-bright deposits in Mercury's northern hemisphere from individual Mercury Laser Altimeter tracks.

The discovery of Mercury's radar-bright deposits has expanded our understanding of volatiles in the solar system. Key to deciphering the history and origin of the radar-bright deposits is an estimate of the volume of radar-bright material that in turn requires a measure of the average thickness of the deposits. In this study we investigate changes in topography across radar-bright deposits hosted in flat-floored, complex craters using individual edited Mercury Laser Altimeter (MLA) tracks. We compare the difference in heights of radar-bright regions and non-radar-bright regions of the crater floor and the difference of similarly sized and located regions in non-radar-bright craters and show that the two populations cannot be distinguished. The similarity of topography in these two sets of craters allows an upper limit of 15 m to be placed on the thickness of the radar-bright deposits.

Planetary science. Low-altitude magnetic field measurements by MESSENGER reveal Mercury's ancient crustal field.

Magnetized rocks can record the history of the magnetic field of a planet, a key constraint for understanding its evolution. From orbital vector magnetic field measurements of Mercury taken by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft at altitudes below 150 kilometers, we have detected remanent magnetization in Mercury's crust. We infer a lower bound on the average age of magnetization of 3.7 to 3.9 billion years. Our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in Mercury's history. Ancient field strengths that range from those similar to Mercury's present dipole field to Earth-like values are consistent with the magnetic field observations and with the low iron content of Mercury's crust inferred from MESSENGER elemental composition data.