A Paleontological Study of the Gunflint Microfossil Assemblage

Precambrian microfossils discovered in nonferruginous charts of the lower algal members of the Gunflint formation of southern Ontario are of great interest in the evolutionary scheme of primitive life. The environment of deposition of the deposit, and the indigenous and biogenic nature of the microfossil assemblage are considered. A discussion of the small but diversified assemblage, including twelve micro-forms, seven of which have not previously been reported, is presented

A Paleontological Study of the Gunflint Microfossil Assemblage

Precambrian microfossils discovered in nonferruginous charts of the lower algal members of the Gunflint formation of southern Ontario are of great interest in the evolutionary scheme of primitive life. The environment of deposition of the deposit, and the indigenous and biogenic nature of the microfossil assemblage are considered. A discussion of the small but diversified assemblage, including twelve micro-forms, seven of which have not previously been reported, is presented

Ritmo e modo da evolução microbiana pré-cambriana

Over the past quarter-century, detailed genus - and species-level similarities in cellular morphology between described taxa of Precambrian microfossils have been noted and regarded as biologically and taxonomically significant by numerous workers worldwide. Such similarities are particularly well-documented for members of the Oscillatoriaceae and Chroococcaceae, the two most abundant and widespread Precambrian cyanobacterial families.For species of two additional families, the Entophysalidaceae and Pleurocapsaceae, species-level morphologic similarities are supported by in-depth fossil-modern comparisons of environment, taphonomy, development, and behavior. Morphologically and probably physiologically as well, such cyanobacterial living fossils have exhibited an extraordinarily slow (hypobradytelic) rate of evolutionary change, evidently a result of the broad ecologic tolerance characteristic of many members of the group (and a striking example of Simpson's "rule of the survival of the relatively unspecialized"). In both tempo and mode of evolution, much of the Precambrian history of life - that dominated by microscopic cyanobacteria and related prokaryotes - appears to have differed markedly from the more recent Phanerozoic evolution of megascopic, horotelic, adaptationally specialized eukaryotes.No decorrer do último quarto de século, semelhanças detalhadas, em níveis de gênero e espécie, entre microfósseis pré-cambrianos e cianobactérias atuais, têm sido repetidamente anotadas e consideradas significativas biológica e taxonómicamente por grande número de pesquisadores espalhados pelo mundo. Estas semelhanças são particularmente bem-documentadas em membros das Oscillatoriaceae e Chroococcaceae, as duas famílias cianobacterianas pré-cambrianas mais amplamente distribuídas e abundantes. Em espécies de duas outras famílias, as Entophysalidaceae e Pleurocapsaceae, semelhanças morfológicas, em nível de espécie, entre fósseis e formas modernas apoiam-se em comparações profundas, abrangendo ambiente, tafonomia, desenvolvimento e comportamento. Morfológica e, provavelmente, fisiológicamente, tais fósseis vivos cianobacterianos evidenciam uma taxa de mudança evolutiva extraordinariamente lenta (hipobraditélica), evidentemente em conseqüência da larga tolerância ecológica característica de muitos membros do grupo, constituindo, assim, notável exemplo da "regra de sobrevivência dos relativamente pouco especializados", elaborada por Simpson. Tanto no ritmo quanto no modo de evolução, muito da história pré-cambriana da vida - aquela parte que foi dominada pelas microscópicas cianobactérias e outros procariotos - parece ter sido marcadamente diferente da evolução mais recente, fanerozóica, dos organismos eucarióticos, megascópicos, especializados e horotélicos

The paleobiological record of photosynthesis

Fossil evidence of photosynthesis, documented in Precambrian sediments by microbially laminated stromatolites, cyanobacterial microscopic fossils, and carbon isotopic data consistent with the presence of Rubisco-mediated CO2-fixation, extends from the present to ~3,500 million years ago. Such data, however, do not resolve time of origin of O2-producing photoautotrophy from its anoxygenic, bacterial, evolutionary precursor. Though it is well established that Earth’s ecosystem has been based on autotrophy since its very early stages, the time of origin of oxygenic photosynthesis, more than 2,450 million years ago, has yet to be established

Morphological Biosignatures and the Search for Life on Mars

This report provides a rationale for the advances in instrumentation and understanding needed to assess claims of ancient and extraterrestrial life made on the basis of morphological biosignatures. Morphological biosignatures consist of bona fide microbial fossils as well as microbially influenced sedimentary structures. To be recognized as evidence of life, microbial fossils must contain chemical and structural attributes uniquely indicative of microbial cells or cellular or extracellular processes. When combined with various research strategies, high-resolution instruments can reveal such attributes and elucidate how morphological fossils form and become altered, thereby improving the ability to recognize them in the geological record on Earth or other planets. Also, before fossilized microbially influenced sedimentary structures can provide evidence of life, criteria to distinguish their biogenic from non-biogenic attributes must be established. This topic can be advanced by developing process-based models. A database of images and spectroscopic data that distinguish the suite of bona fide morphological biosignatures from their abiotic mimics will avoid detection of false-positives for life. The use of high-resolution imaging and spectroscopic instruments, in conjunction with an improved knowledge base of the attributes that demonstrate life, will maximize our ability to recognize and assess the biogenicity of extraterrestrial and ancient terrestrial life

Calcitization of aragonitic bryozoans in Cenozoic tropical carbonates from East Kalimantan, Indonesia

© The Author(s) 2016. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The file attached is the published version of the article

As the Walls of Academia are Tumbling Down

http://deepblue.lib.umich.edu/bitstream/2027.42/58008/1/2717844392.pd

Measurement of the inclusive isolated-photon cross section in pp collisions at √s = 13 TeV using 36 fb−1 of ATLAS data

The differential cross section for isolated-photon production in pp collisions is measured at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC using an integrated luminosity of 36.1 fb. The differential cross section is presented as a function of the photon transverse energy in different regions of photon pseudorapidity. The differential cross section as a function of the absolute value of the photon pseudorapidity is also presented in different regions of photon transverse energy. Next-to-leading-order QCD calculations from Jetphox and Sherpa as well as next-to-next-to-leading-order QCD calculations from Nnlojet are compared with the measurement, using several parameterisations of the proton parton distribution functions. The predictions provide a good description of the data within the experimental and theoretical uncertainties. [Figure not available: see fulltext.

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements