Frozen in Time: Concepts of 'Global Glaciation' from 1837 (die Eiszeit) to 1998 (the Snowball Earth)

A completely ice-bound Earth, where life is arrested by extreme cold, is not a story out of science fiction but has been proposed to explain Neoproterozoic paleobiology and climates. The Snowball Earth hypothesis is the subject of considerable media interest on a par with global warming. The basic premise was originally outlined in 1837 by Louis Agassiz in his famous Discours de Neuchatel, in which he set out the case for die Eiszeit, a geologically recent Great Ice Age that had smothered the tropics and wiped out all life. A divine creator then introduced new species. Following widespread dismissal of Agassiz's controversial claim to have discovered glacial deposits in the Amazon in 1866, the idea fell out of favour. The concept of ancient 'globally-engulfing glaciations' was given new life in the early 1930s by T. Gevers as the geology of the continents was mapped and the intercontinental distribution of Permo-Carboniferous and Precambrian glacial tillites became evident. To 'permanentists' such as the Toronto glacialist A.P. Coleman, who rejected Wegener's drifting continents explanation for widespread Permo-Carboniferous glacial deposits, the presence of tillites in the steamy heat of the tropics necessitated equatorial ice sheets when 'a world found itself in the grip of the fiercest... of the ice ages'. Similarly, in reference to the late Precambrian record, D. Mawson referred to the 'world-wide nature of the Earth's greatest glaciation' in 1949. After a brief intermission, when the glacial origin and climatic significance of many deposits was questioned, the ideal of low-latitude glaciation was resurrected in 1964 as the 'great infra-cambrian glaciation' of W.B. Harland. In the early 1970s, L.J.G. Schermerhorn countered by showing that many alleged 'tillites' were the result of submarine mass flow in tectonically active basins. Notwithstanding these findings, fears of 'nuclear winter' arising from nuclear conflagration reawakened interest in an ice-bound Earth in the late 1980s. This culminated in P. Hoffman's and J.L. Kirschvink's Neoproterozoic Snowball Earth model of severe, ten million-year-long global refrigerations when temperatures plummeted to -50°C, the world's oceans froze and all planetary biological activity was arrested only to be revived during short, brutal interglacials. These so-called 'freeze-fry' episodes are thought to have been a precursor to the Cambrian 'explosion'. In this paper I expand on the historical development of the idea over the past 160 years and show that the current 'Snowball' version is based on several premises of 'permanentist' thinking that arose in opposition to Wegener in the 1920s and that have survived the advent of plate tectonics and sedimentology largely intact. RÉSUMÉ Une Terre complètement enserrée dans la glace, où la vie a été suspendue par le froid, ce n'est pas une idée de science fiction, mais une idée qui a déjà été proposée pour expliquer la paléobiologie et les climats du Néoprotérozoïque. L'hypothèse d'une Terre « boule de neige » fait l'objet d'autant d'attention des médias que l'idée d'un réchauffement de la planète. La prémisse de base en a été décrite en 1837 par Louis Agassiz dans son fameux « Discours de Neuchâtel », document où il plaidait pour die Eiszeit (temps de glace), un grand âge glaciaire géologiquement récent qui aurait envahi les tropiques et éliminé toute vie. Un créateur divin aurait depuis créé de nouvelles espèces. Puis, avec le rejet généralisé de la prétention d'Agassiz d'avoir découvert des dépôts glaciaires en Amazonie en 1866, l'idée a été oubliée. Au début des années 1930, T. Gevers a redonné vie au concept « d'anciennes glaciations planétaires », à la faveur de la cartographie géologique des continents, alors qu'a été mis en évidence l'existence de tillites glaciaires permo-carbonifères et précambriennes. Du point de vue des « fixistes » comme le glacielliste de Toronto A. P. Coleman, lequel rejetait l'idée de dérive des continents de Wegener pour expliquer la distribution permo-carbonifère des dépôts glaciaires, l'existence de tillites dans les zones tropicales chaudes et humides impliquaient obligatoirement l'existence de lentilles glaciaires équatoriales, alors « (traduction) ... que le monde s'est trouvé aux prises avec de terribles âges glaciaires ». De même, se référant à des dépôts de la fin du Précambrien, D. Mawson en 1949, évoquait « (traduction) la nature globale de l'étendue de la plus grande glaciation de la Terre ». Ensuite, après un bref intermède, alors que l'origine et la nature glaciaire de nombreux dépôts était remise en question, l'idée de glaciation à de basses latitudes a été ressuscitée en 1964 par W. B. Harland « (traduction) la grande glaciation infracambrienne ». Au début des années 1970, L. J. G. Schermeerhorn a contreattaqué en montrant que nombre de ces présumées tillites n'étaient que la résultante de coulées sédimentaires sous-marines dans des bassins techniquement actifs. Malgré ces découvertes, vers la fin des années 1980, la peur d'un « hiver nucléaire » résultant d'une conflagration nucléaire a vu renaître l'intérêt pour l'idée d'une Terre englacée. Ce dernier épisode a connu son apogée avec le modèle de P. Hoffman et de J. L. Kirschivink d'une Terre « boule de neige » au Néoprotérozoïque, soit un période frigorifique de dix millions d'années, la température chutant à -50°C, les océans étant gelés et où toute activité biologique était stoppée, sauf pour quelques périodes interglaciaires brutales de courtes durées. Ces épisodes d'alternance chaud-froid auraient été à l'origine de « l'explosion » Cambrienne. Dans le présent article j'explique l'évolution historique de cette idée au cours des derniers 160 ans, et je démontre que l'actuel concept de « boule de neige » repose sur plusieurs prémisses de la mouvance « fixiste » qui s'est fait jour en opposition à Wegener dans les années 1920, laquelle a survécue sans être vraiment affectée par les développements de la tectonique des plaques et de la sédimentologie

Glaciolacustrine Sedimentation During Advance and Retreat of the Cordilleran Ice Sheet in Central British Colombia

Thick (400+ m) and well exposed sediment fills in the Fraser and Chilcotin river valleys of central British Columbia record contrasting glaciolacustrine environments of at least two glaciations. The oldest glaciolacustrine sequence comprises deformed gravel, sand, mud, and diamict fades deposited, in part, on stagnant ice trapped in deep narrow valleys at the end of the penultimate glaciation (Early Wisconsinan or older). Younger glaciolacustrine sequences date from the advance and retreat phases of the Late Wisconsinan Fraser Glaciation {ca. 25-10 ka) and infill a Middle Wisconsinan drainage system cut across older sediments. The Late Wisconsinan advance sequence is dominated by diamict (debris-flow) fades that pass upward into silts. The diamict fades consist largely of reworked older Pleistocene drift and poorly lithified Cretaceous and Tertiary sediments. They record the focusing of large volumes of sediment into one or more glacial lakes occupying deep narrow troughs. Weakly bedded silts in the upper part of the sequence may have been deposited when the lake(s) deepened as glaciers continued to advance and thicken over the study area. It is possible that some advance glaciolacustrine sediments accumulated in subglacial water bodies. Late Wisconsinan deglacial lake sediments form a relatively thin, discontinuous capping in the area and conform to classical notions of gladolacustrine sedimentation involving a seasonal or 'varved' regime. In contrast, no seasonal pattern of sedimentation can be identified in older sequences where the overriding influence on deposition has been the presence of steep subaqueous slopes, buried ice masses, and high sediment fluxes; these, in combination, caused near-continuous downslope movement and resedimentation.Les épaisses accumulations de sédiments (400+ m) qui comblent les vallées du Fraser et de la Chilcotin River permettent de distinguer les milieux glaciola-custres issus d'au moins deux glaciations. La séquence glaciolacustre la plus ancienne comprend des faciès déformés de gravier, sable, boue et diamicton mis en place, en partie, sur une glace stagnante emprisonnée dans de profondes vallées étroites à la fin de l'avant-dernière glaciation (Wisconsinien inférieur ou avant). Les séquences glaciolacustres plus récentes datent des phases d'avancée et de retrait de la Glaciation de Fraser au Wisconsinien supérieur (vers 25-10 ka) et ont comblé un réseau de drainage du Wisconsinien moyen entaillé dans des sédiments plus anciens. La séquence d'avancée glaciaire du Wisconsinien supérieur est dominée par un faciès de diamicton (coulée de débris) remplacé vers le haut par des silts. Le faciès de diamicton est en grande partie constitué de dépôts glaciaires anciens du Pleistocene remaniés et de sédiments peu consolidés du Crétacé et du Tertiaire. Ils témoignent de l'accumulation de grandes quantités de sédiments dans un ou plusieurs lacs glaciaires resserrés dans des dépressions profondes et étroites. Dans la partie supérieure de la séquence, les silts faiblement stratifiés ont probablement été mis en place lorsque les lacs se sont approfondis avec l'avancée des glaciers. Il est possible que des sédiments glaciolacustres se soient accumulés dans des nappes sous-glaciaires au cours de l'avancée glaciaire. Les sédiments lacustres de retrait glaciaire du Wisconsinien supérieur forment une mince couverture discontinue et se sont déposés selon un régime saisonnier ou varvaire.Dicke (+ 400m) und gut ausgesetzte Sediment-fùllungen in den Fraser- und Chilcotin-Flusstalern im Zentrum von British Columbia bezeugen kontrastierende glaziallimnische Umwelten von mindestens zwei Vereisungen. Die àlteste glaziallimnische Sequenz besteht aus deformierten Fazies aus Kies, Sand, Schlamm und Diamikton, die zum Teil auf stagnierendem Eis abgelagert wurden, das in tiefen, engen Tàlern am Ende der vorletzten Vereisung (frûhes Wisconsin oder alter) fest-steckte. Jûngere glaziallimnische Sequenzen stammen von den Vorstoss- und Rùckzugsphasen der Fraser-Vereisung im spaten Wisconsin (etwa 25-10 ka) und haben ein Drânage-System des mittleren Wisconsin, das sich quer durch altère Sedimente eingekerbt hat, ausgefùiit. Die Vorstoss-Sequenz aus dem spaten Wisconsin wird von Diamikton (Trûmmer-Strômung)-Fazies beherrscht, die nach oben hin in Schlamm ùbergehen. Die Diamikton-Fazies bestehen weitgehend aus umgearbeiteten âlteren glazialen Ablagerungen aus dem Pleistozân und gering verfestigten Sedimenten aus der Kreidezeit und dem Tertiàr. Sie bezeugen die Konzentration grosser Sedimentvolumen in einem oder mehreren glazialen Seen, die sich in tiefen engen Trôgen befanden. Schwach geschichteter Schlamm im oberen Teil der Sequenz ist môglicherweise abgelagert worden, als der See/die Seen tiefer wurden, wàhrend die Gletscher ùber dem untersuchten Gebiet weiter vorstiessen und sich verdickten. Es ist môglich, dass einige glaziallimnische Vorstoss-Sedimente sich in subglazialen Wasserflâchen akkumulierten. Glaziale Seen-Rùckzugssedimente aus dem spaten Wisconsin bilden in dem Gebiet eine relativ dûnne, nichtkontinuierliche Decke und ent-sprechen der klassischen Vorstellung glazial-limnischer Sedimentierung mit periodischem oder "Warwen"-System

The Bedrock Surface of the Western Lake Ontario Region: Evidence of Reactivated Basement Structures?

Lower Paleozoic bedrock strata, in south-central Ontario and the adjacent part of New York State are covered by a thick (100m+) blanket of Pleistocene glacial and interglacial sediments. The form of the buried bedrock surface has been reconstructed from 70,000 waterwell boreholes that extend through the entire Pleistocene cover using GIS data processing techniques. The sub-drift bedrock surface shows linear channels that connect the basins of lakes Huron, Ontario and Erie and which form part of an ancestral mid-continent Great Lake drainage system prior to modification and infilling during successive Pleistocene glaciations. This relict drainage system is cut across Lower Paleozoic carbonates and elastics up to 500 m thick, but the position of several channels is aligned above terrane boundaries, faults and other deep-seated and poorly understood geophysical anomalies in underlying mid-Proterozoic Grenville basement rocks. Other channels are controlled by a dominant northwest and northeast trending regional joint system. A close relationship among deeply seated geophysical lineaments, basement structures and topographic lineaments cut across thick Paleozoic cover strata suggests a history of Phanerozoic reactivation and upward propagation of fractures from the Precambrian basement. Several basement structures and lineaments are seismically active suggesting ongoing neotectonic activity across the 'stable' craton of south-central Ontario.La surface de la roche de fond dans la partie ouest du lac Ontario: indices de réactivation des structures du socle. Les couches géologiques de la roche de fond du Paléozoïque inférieur, dans le centre sud de l'Ontario et la partie adjacente de l'État de New York, sont recouvertes par une grande épaisseur (> 100 m) de sédiments glaciaires et interglaciaires. La forme de la surface de la roche de fond enfouie a été reconstituée à partir de 70 000 puits de sondage qui traversent toute la couverture du Pleistocene. La surface sous les dépôts glaciaires laisse voir des chenaux linéaires qui relient les bassins des lac Hurons, Ontario et Érié et qui forment une partie de l'ancien système de drainage des Grands Lacs. Ce réseau de drainage relique entaille les carbonates du Paléozoïque inférieur et les dépôts détritiques jusqu'à 500 m d'épaisseur, mais l'emplacement de plusieurs chenaux est aligné au-dessus des limites de la formation fissurée, des failles et autres anomalies géophysiques profondes et mal connues du socle grenvillien du Protérozoïque moyen. D'autres chenaux sont sous la dépendance d'un réseau de fractures en grande partie orientées vers le NW et vers le NE. Les fortes relations qui existent entre les linéaments géophysiques profonds, les structures du socle et les linéaments topographiques entaillant l'épaisse couverture paléozoïque laissent entrevoir une réactivation au Phanérozoïque et une propagation ascendante des fractures à partir du socle précambrien. Plusieurs structures et linéaments du socle sont sismiquement actifs signalant ainsi une activité néotectonique continue à travers tout le craton dit stable du centre-sud de l'Ontario.Die Sockelstrata aus dem unteren Palàozoikum im sùdlichen Zentrum von Ontario und dem angrenzenden Teil des Staates New York sind von einer dicken (100 m+) Decke glazialer und interglazialer Pleistozànsedimente ùberlagert. Die Form der vergrabenen Oberflache des Sockels ist mittles 70 000 Brunnenbohrlôchern, die durch die ganze Pleistozândecke hindurch-gehen, rekonstruiert worden. Die Sockeloberglàche unter den glazialen Ablagerungen zeigt lineare Rinnen, welche die Becken des Huron-, Ontario-und Eriesees miteinander verbinden und Teil eines alten halbkontinentalen Drainage-systems der Grofîen Seen bilden. Dieses Reliktdrainagesystem schneidet quer durch die Karbonate des unteren Palàozoikums und die Trùmmergesteine bis zu einer Dicke von 500 m, aber die Position gewisser Rinnen ist oberhalb der Grenzen der gespaltenen Foramation, den Verwerfungen und anderen tiefgelegenen und schlecht verstandenen geophysikalischen Anomalien der darunterliegenden Felsen des Grenville-Unterbaus aus dem mittleren Palàozoikum ausgerichtet. Andere Rinnen werden durch ein régionales Kluftsystem, das vor allem nach Nordwesten und Nordosten ausgerichtet ist, kontrolliert. Eine enge Beziehung zwischen tief gelegenen geophysikalischen Lineamenten, Unterbaustrukturen und topographischen Lineamenten, deuten auf eine Reaktivierung im Phanàrozoikum und eine aufsteigende Verbreitung der Bruche vom Unterbau des Pràkambriums. Mehrere Unterbaustrukturen und Lineamente sind seismisch aktiv und zeigen so eine anhaltende neotektonische Aktivitàt quer durch den als "Stabil" angesehenen Kraton vom sùdlichen Zentrum Ontarios

Composite suspended sediment particles and flocculation in glacial meltwaters: preliminary evidence from Alpine and Himalayan basins

Research over the last decade has shown that the suspended sediment loads of many rivers are dominated by composite particles. These particles are also known as aggregates or flocs, and are commonly made up of constituent mineral particles, which evidence a wide range of grain sizes, and organic matter. The resulting in situ or effective particle size characteristics of fluvial suspended sediment exert a major control on all processes of entrainment, transport and deposition. The significance of composite suspended sediment particles in glacial meltwater streams has, however, not been established. Existing data on the particle size characteristics of suspended sediment in glacial meltwaters relate to the dispersed mineral fraction (absolute particle size), which, for certain size fractions, may bear little relationship to the effective or in situ distribution. Existing understanding of composite particle formation within freshwater environments would suggest that in-stream flocculation processes do not take place in glacial meltwater systems because of the absence of organic binding agents. However, we report preliminary scanning electron microscopy data for one Alpine and two Himalayan glaciers that show composite particles are present in the suspended sediment load of the meltwater system. The genesis and structure of these composite particles and their constituent grain size characteristics are discussed. We present evidence for the existence of both aggregates, or composite particles whose features are largely inherited from source materials, and flocs, which represent composite particles produced by instream flocculation processes. In the absence of organic materials, the latter may result solely from electrochemical flocculation in the meltwater sediment system. This type of floc formation has not been reported previously in the freshwater fluvial environment. Further work is needed to test the wider significance of these data and to investigate the effective particle size characteristics of suspended sediment associated with high concentration outburst events. Such events make a major contribution to suspended sediment fluxes in meltwater streams and may provide conditions that are conducive to composite particle formation by flocculation

Do patients with femoroacetabular impingement syndrome who undergo hip arthroscopy display improved alpha angle (magnetic resonance imaging) and radiographic hip morphology?

AIMS To compare (a) the change in radiological bony morphology between participants with femoroacetabular impingement (FAI) syndrome who underwent arthroscopic hip surgery compared to physiotherapist-led non-surgical care and (b) the change in radiological bony morphology between participants with FAI syndrome who underwent arthroscopic hip surgery involving cam resection or acetabular rim trimming or combined cam resection and acetabular rim trimming. METHODS Maximum alpha angle measurements on magnetic resonance imaging and Hip2 Norm standardized hip measurements on radiographs were recorded at baseline and at 12 months postoperatively. One-way analysis of covariance and independent T tests were conducted between participants who underwent arthroscopic hip surgery and physiotherapist-led non-surgical care. Independent T tests and analysis of variance were conducted between participants who underwent the 3 different arthroscopic hip procedures. RESULTS Arthroscopic hip surgery resulted in significant improvements to mean alpha angle measurements (decreased from 70.8° to 62.1°) (P value < .001, 95% CI -11.776, -4.772), lateral center edge angle (LCEA) (P value = .030, 95% CI -3.403, -0.180) and extrusion index (P value = 0.002, 95% CI 0.882, 3.968) compared to physiotherapist-led management. Mean maximum 1-year postoperative alpha angle was 59.0° (P value = .003, 95% CI 4.845, 18.768) for participants who underwent isolated cam resection. Measurements comparing the 3 different arthroscopic hip procedures only differed in total femoral head coverage (F[2,37] = 3.470, P = .042). CONCLUSION Arthroscopic hip surgery resulted in statistically significant improvements to LCEA, extrusion index and alpha angle as compared to physiotherapist-led management. Measured outcomes between participants who underwent cam resection and/or acetabular rim trimming only differed in total femoral head coverage

Moderators, Mediators, and Prognostic Indicators of Treatment With Hip Arthroscopy or Physical Therapy for Femoroacetabular Impingement Syndrome: Secondary Analyses From the Australian FASHIoN Trial.

BACKGROUND Although randomized controlled trials comparing hip arthroscopy with physical therapy for the treatment of femoroacetabular impingement (FAI) syndrome have emerged, no studies have investigated potential moderators or mediators of change in hip-related quality of life. PURPOSE To explore potential moderators, mediators, and prognostic indicators of the effect of hip arthroscopy and physical therapy on change in 33-item international Hip Outcome Tool (iHOT-33) score for FAI syndrome. STUDY DESIGN Cohort study; Level of evidence, 2. METHODS Overall, 99 participants were recruited from the clinics of orthopaedic surgeons and randomly allocated to treatment with hip arthroscopy or physical therapy. Change in iHOT-33 score from baseline to 12 months was the dependent outcome for analyses of moderators, mediators, and prognostic indicators. Variables investigated as potential moderators/prognostic indicators were demographic variables, symptom duration, alpha angle, lateral center-edge angle (LCEA), Hip Osteoarthritis MRI Scoring System (HOAMS) for selected magnetic resonance imaging (MRI) features, and delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) score. Potential mediators investigated were change in chosen bony morphology measures, HOAMS, and dGEMRIC score from baseline to 12 months. For hip arthroscopy, intraoperative procedures performed (femoral ostectomy ± acetabular ostectomy ± labral repair ± ligamentum teres debridement) and quality of surgery graded by a blinded surgical review panel were investigated for potential association with iHOT-33 change. For physical therapy, fidelity to the physical therapy program was investigated for potential association with iHOT-33 change. RESULTS A total of 81 participants were included in the final moderator/prognostic indicator analysis and 85 participants in the final mediator analysis after exclusion of those with missing data. No significant moderators or mediators of change in iHOT-33 score from baseline to 12 months were identified. Patients with smaller baseline LCEA (β = -0.82; P = .034), access to private health care (β = 12.91; P = .013), and worse baseline iHOT-33 score (β = -0.48; P < .001) had greater iHOT-33 improvement from baseline to 12 months, irrespective of treatment allocation, and thus were prognostic indicators of treatment response. Unsatisfactory treatment fidelity was associated with worse treatment response (β = -24.27; P = .013) for physical therapy. The quality of surgery and procedures performed were not associated with iHOT-33 change for hip arthroscopy (P = .460-.665 and P = .096-.824, respectively). CONCLUSION No moderators or mediators of change in hip-related quality of life were identified for treatment of FAI syndrome with hip arthroscopy or physical therapy in these exploratory analyses. Patients who accessed the Australian private health care system, had smaller LCEAs, and had worse baseline iHOT-33 scores, experienced greater iHOT-33 improvement, irrespective of treatment allocation

Recombinant Newcastle disease virus immunotherapy drives oncolytic effects and durable systemic antitumor immunity

A recombinant Newcastle Disease Virus (NDV), encoding either a human (NDVhuGM-CSF, MEDI5395) or murine (NDVmuGM-CSF) GM-CSF transgene, combined broad oncolytic activity with ability to significantly modulate genes related to immune functionality in human tumor cells. Replication in murine tumor lines was significantly diminished relative to human tumor cells. Nonetheless, intratumoral injection of NDVmuGM-CSF conferred antitumor effects in three syngeneic models in vivo; with efficacy further augmented by concomitant treatment with anti-PD-1/L-1 or T cell agonists. Ex vivo immune-profiling, including TCRseq, revealed profound immune-contexture changes; consistent with priming and potentiation of adaptive immunity and tumor-microenvironment (TME) re-programming towards an immune-permissive state. CRISPR modifications rendered CT26 significantly more permissive to NDV replication, and in this setting NDVmuGM-CSF confers immune-mediated¬¬¬¬¬¬ effects in the non-injected tumor in vivo. Taken together the data supports the thesis that MEDI5395 primes and augments cell mediated antitumor immunity and has significant utility as a combination partner with other immunomodulatory cancer treatments