scholarly journals Paleoarchean trace fossils in altered volcanic glass

2015 ◽  
Vol 112 (22) ◽  
pp. 6892-6897 ◽  
Author(s):  
Hubert Staudigel ◽  
Harald Furnes ◽  
Maarten DeWit
Keyword(s):  
Critical Evaluation ◽  
Volcanic Glass ◽  
Trace Fossils ◽  
Deep Biosphere ◽  
Basalt Glass ◽  
Pillow Lavas ◽  
Cenozoic Basalt ◽  
Basalt Glasses ◽  
Evaluation Of Evidence ◽  
Life On Earth

Microbial corrosion textures in volcanic glass from Cenozoic seafloor basalts and the corresponding titanite replacement microtextures in metamorphosed Paleoarchean pillow lavas have been interpreted as evidence for a deep biosphere dating back in time through the earliest periods of preserved life on earth. This interpretation has been recently challenged for Paleoarchean titanite replacement textures based on textural and geochronological data from pillow lavas in the Hooggenoeg Complex of the Barberton Greenstone Belt in South Africa. We use this controversy to explore the strengths and weaknesses of arguments made in support or rejection of the biogenicity interpretation of bioalteration trace fossils in Cenozoic basalt glasses and their putative equivalents in Paleoarchean greenstones. Our analysis suggests that biogenicity cannot be taken for granted for all titanite-based textures in metamorphosed basalt glass, but a cautious and critical evaluation of evidence suggests that biogenicity remains the most likely interpretation for previously described titanite microtextures in Paleoarchean pillow lavas.

scholarly journals Pathways for abiotic organic synthesis at submarine hydrothermal fields

2015 ◽  
Vol 112 (25) ◽  
pp. 7668-7672 ◽  
Author(s):  
Jill M. McDermott ◽  
Jeffrey S. Seewald ◽  
Christopher R. German ◽  
Sean P. Sylva
Keyword(s):  
Organic Compounds ◽  
Organic Synthesis ◽  
Deep Sea ◽  
Hot Springs ◽  
Hydrothermal Systems ◽  
Deep Biosphere ◽  
Shallow Subsurface ◽  
Microbial Life ◽  
Abiotic Organic Synthesis ◽  
Life On Earth

Arguments for an abiotic origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H2-rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the abiotic generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for abiotic organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H2 generation during active serpentinization. Rather, our results indicate that CH4 found in vent fluids is formed in H2-rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond.

Progesterone for the prevention of preterm birth: A critical evaluation of evidence

2006 ◽  
Vol 129 (2) ◽  
pp. 111-118 ◽  
Author(s):  
Aravinthan Coomarasamy ◽  
Shakila Thangaratinam ◽  
Harry Gee ◽  
Khalid S Khan
Keyword(s):  
Preterm Birth ◽  
Critical Evaluation ◽  
Evaluation Of Evidence

How Can Educators Confront Science Denial?

2019 ◽  
Vol 48 (4) ◽  
pp. 229-238 ◽  
Author(s):  
Rebekka Darner
Keyword(s):  
Theoretical Model ◽  
Critical Evaluation ◽  
Motivated Reasoning ◽  
Psychological Needs ◽  
Basic Psychological Needs ◽  
Self Determination ◽  
Informed Citizenry ◽  
Understanding Of Science ◽  
Evaluation Of Evidence ◽  
Backfire Effect

An unwillingness to consider empirical evidence that contradicts one’s desired conclusion, or science denial, is an enormous barrier to producing an informed citizenry. This essay explores literature on conceptual change and motivation to put forth fresh ideas on how curricula can foster science acceptance, or the willingness to engage in critical evaluation of evidence even when it holds potential to contradict one’s preferred conclusion. Drawing from motivated reasoning and self-determination theories, this essay builds a theoretical model of how negative emotions, thwarting of basic psychological needs, and the backfire effect interact to undermine critical evaluation of evidence, leading to science denial. The model guides the proposal of several design principles for creating instruction that is likely to foster science acceptance, and puts forth the evidence-laden narrative as an exemplar. This essay calls for instructional methods that facilitate motivation toward accuracy goals by fulfilling basic psychological needs as students engage in accuracy-oriented reasoning while evaluating evidence. The conclusion suggests further lines of research that might improve our understanding of science denial and how it can be confronted in the classroom.

Weathered Basalt Glass: A Natural Analogue for the Effects of REACTION Progress on Nuclear Waste Glass Alteration

1985 ◽  
Vol 50 ◽  
Author(s):  
B. Grambow ◽  
M. J. Jercinovic ◽  
R. C. Ewing ◽  
C. D. Byers
Keyword(s):  
Nuclear Waste ◽  
Laboratory Experiments ◽  
Reaction Rates ◽  
Similar Reaction ◽  
Natural Analogue ◽  
Reaction Progress ◽  
Basalt Glass ◽  
Basalt Glasses ◽  
Analogous Behavior

AbstractLaboratory experiments alone cannot be used to verify models for the long-term release of radionuclides from nuclear waste glasses. Basalt glasses have been proposed as an appropriate natural analogue for the long-term validation of release models [1]. Their analogous behavior has been demonstrated in laboratory experiments in which both types of glasses display similar reaction rates, alteration products and surface layer morphologies [2,3]. This paper illustrates how empirical data from natural occurrences of basalt glass can be interpreted by a model which is developed to describe the reaction progress of the corrosion of nuclear waste form borosilicate glass [4,5].

Prehistory from Antipodean Perspectives

1971 ◽  
Vol 37 (2) ◽  
pp. 228-252 ◽  
Author(s):  
D. J. Mulvaney
Keyword(s):  
New Zealand ◽  
Critical Evaluation ◽  
Distribution Map ◽  
Pacific World ◽  
Inaugural Lecture ◽  
The Pacific ◽  
Evaluation Of Evidence ◽  
Cambridge School

My initial Australian fieldwork was still a year ahead when, surprisingly, I featured anonymously on a verbal distribution map confidently sketched by the Disney Professor. I was the ‘Australia’ reference of his Inaugural lecture, thereby illustrating his proposition (Clark, 1954, 33), that ‘the geographical field of Cambridge prehistorians has been … the whole world’. My Cambridge contemporaries, Sieveking and Golson, respectively represented ‘Malaya’ and ‘New Zealand’.We were indeed the forerunners of a sizeable band of hunter-diggers which ventured into the Pacific world and which numbers Cambridge amongst its totemic centres. Such incipient, though benevolent imperialism, has not gone unchallenged. A participant in an Australian archaeological congress recently deplored what he judged to be the errors and dogmatism of the ‘Cambridge school’. He erred in affixing this label, because there is no such implicit cohesion within the ranks; diversity is already a healthy characteristic of Pacific research.What was relevant about Cambridge training, but no more so than of any sound methodological discipline, was that it encouraged respect for, and critical evaluation of, evidence. What was intellectually satisfying to the student were the concepts of universality and interdependence in past human affairs. Such is the message from Miles Burkitt's Prehistory to Grahame Clark's World Prehistory.

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