The Fundamental Role Of Giant Comets In Earth History

1992 ◽  
pp. 179-193
Author(s):  
S.V.M. Clube
Keyword(s):  
Earth History ◽  
Giant Comets

The fundamental role of giant comets in earth history

1992 ◽  
Vol 54 (1-3) ◽  
pp. 179-193 ◽  
Author(s):  
S. V. M. Clube
Keyword(s):  
Earth History ◽  
Giant Comets

scholarly journals Major features of protistan evolution: controversies, problems and a few answers

2006 ◽  
Vol 29 (1) ◽  
pp. 55-80
Author(s):  
Jere H Lipps
Keyword(s):  
Fossil Record ◽  
Molecular Data ◽  
Trophic Levels ◽  
Early Earth ◽  
Huge Number ◽  
Geologic Time ◽  
Earth History ◽  
Important Development ◽  
Fossil Evidence

The major features of protist evolution are fraught with controversies, problems and few answers, especially in early Earth history. In general they are based on molecular data and fossil evidence that respectively provide a scaffold and details of eukaryotic phylogenetic and ecologic histories. 1. Their origin, inferred from molecular sequences, occurred very early (>;3Ga). They are a chimera of different symbiont-derived organelles, including possibly the nucleus. 2. The initial diversification of eukaryotes may have occurred early in geologic time. Six supergroups exist today, each with fossils known from the Proterozoic and Phanerozoic. 3. Sex, considered an important development, may have been inherited from bacteria. 4. Precambrian protists were largely pelagic cyst-bearing taxa, but benthic forms were probably quite diverse and abundant. 5. Protists gave rise to animals long before 600 Ma through the choanoflagellates, for which no fossil record exists. 6. Acritarchs and skeletonized protists radiated in the Cambrian (544-530 my). From then on, they radiated and became extinct at all the major events recorded in the metazoan fossil record. 7. Protists dominated major environments (shelves and reefs) starting with a significant radiation in the Ordovician, followed by extinctions and other radiations until most died out at the end of the Permian. 8. In the Mesozoic, new planktic protozoa and algae appeared and radiated in pelagic environments. 9. Modern protists are important at all trophic levels in the oceans and a huge number terrestrial, parasitic and symbiotic protists must have existed for much of geologic time as well. 10. The future of protists is likely in jeopardy, just like most reefal, benthic, and planktic metazoans. An urgent need to understand the role of protists in modern threatened oceans should be addressed soon.

scholarly journals Limited role for methane in the mid-Proterozoic greenhouse

2016 ◽  
Vol 113 (41) ◽  
pp. 11447-11452 ◽  
Author(s):  
Stephanie L. Olson ◽  
Christopher T. Reinhard ◽  
Timothy W. Lyons
Keyword(s):  
Radiative Forcing ◽  
System Model ◽  
Low Latitude ◽  
Earth History ◽  
Subsurface Ocean ◽  
Low Levels ◽  
Earth’S Climate ◽  
Geologic Record ◽  
Marine Biosphere

Pervasive anoxia in the subsurface ocean during the Proterozoic may have allowed large fluxes of biogenic CH4to the atmosphere, enhancing the climatic significance of CH4early in Earth’s history. Indeed, the assumption of elevatedpCH4during the Proterozoic underlies most models for both anomalous climatic stasis during the mid-Proterozoic and extreme climate perturbation during the Neoproterozoic; however, the geologic record cannot directly constrain atmospheric CH4levels and attendant radiative forcing. Here, we revisit the role of CH4in Earth’s climate system during Proterozoic time. We use an Earth system model to quantify CH4fluxes from the marine biosphere and to examine the capacity of biogenic CH4to compensate for the faint young Sun during the “boring billion” years before the emergence of metazoan life. Our calculations demonstrate that anaerobic oxidation of CH4coupled to SO42−reduction is a highly effective obstacle to CH4accumulation in the atmosphere, possibly limiting atmosphericpCH4to less than 10 ppm by volume for the second half of Earth history regardless of atmosphericpO2. If recentpO2constraints from Cr isotopes are correct, we predict that reduced UV shielding by O3should further limitpCH4to very low levels similar to those seen today. Thus, our model results likely limit the potential climate warming by CH4for the majority of Earth history—possibly reviving the faint young Sun paradox during Proterozoic time and challenging existing models for the initiation of low-latitude glaciation that depend on the oxidative collapse of a steady-state CH4greenhouse.

Charles Lyell’s Principles of Geology, the Geological Sublime, and the Romantic Theatre

2018 ◽  
Vol 45 (2) ◽  
pp. 254-269
Author(s):  
Alexis Harley
Keyword(s):  
Natural Philosophy ◽  
Charles Lyell ◽  
Earth History ◽  
Points Of View ◽  
Principles Of Geology ◽  
Viewing Position

Across the three volumes of his influential Principles of Geology (1830–33), Charles Lyell demonstrates that the scale of earth history is out of all proportion to human temporality. Lyell makes the case that geologists should assume a viewing position outside the drama of geological action. He repeatedly represents this distance through the figure of the theatre, invoking Romantic critiques of theatrical naturalism that aligned with developments in natural philosophy. At the same time, Lyell deployed technologies from the contemporary stage in his public lectures, and in personal correspondence, he reveals promiscuous tastes across genres, forms and sites of performance. Ultimately, I argue, these apparent inconsistencies point to the role of his subjectivity in a project that is deeply ambivalent about human points of view.

Darwin, Concepción, and the Geological Sublime

2012 ◽  
Vol 25 (1) ◽  
pp. 49-71 ◽  
Author(s):  
Paul White
Keyword(s):  
Nineteenth Century ◽  
Popular Science ◽  
Early Nineteenth Century ◽  
Earth History ◽  
The Sublime ◽  
The Earth ◽  
History Of ◽  
The Aesthetic ◽  
Popular Audience

ArgumentDarwin's narrative of the earthquake at Concepción, set within the frameworks of Lyellian uniformitarianism, romantic aesthetics, and the emergence of geology as a popular science, is suggestive of the role of the sublime in geological enquiry and theory in the early nineteenth century. Darwin's Beagle diary and later notebooks and publications show that the aesthetic of the sublime was both a form of representing geology to a popular audience, and a crucial structure for the observation and recording of the event from the beginning. The awesome spectacle of the earthquake proved in turn the magnitude of the forces at stake in earth history, and helped to make geology an epic conjoining the history of civilization with the history of the earth.

The Role of Rapid Events in Earth History

1970 ◽  
Vol 18 (1) ◽  
pp. 42-43
Author(s):  
Donald H. Zenger
Keyword(s):  
Earth History

Role of dactinomycin in the improved survival of children with Wilms' tumor

JAMA ◽  
1966 ◽  
Vol 195 (12) ◽  
pp. 1005-1009 ◽  
Author(s):  
D. J. Fernbach
Keyword(s):  
Wilms Tumor

Role of the allergist in diagnosis and management of patients with uveitis

JAMA ◽  
1966 ◽  
Vol 195 (3) ◽  
pp. 167-172 ◽  
Author(s):  
T. E. Van Metre
Keyword(s):  
Diagnosis And Management

The power of norms to sway fused group members

2018 ◽  
Vol 41 ◽  
Author(s):  
Winnifred R. Louis ◽  
Craig McGarty ◽  
Emma F. Thomas ◽  
Catherine E. Amiot ◽  
Fathali M. Moghaddam
Keyword(s):  
Evolutionary Anthropology ◽  
Normative Systems ◽  
Violent Extremism ◽  
Identity Fusion ◽  
Group Members

AbstractWhitehouse adapts insights from evolutionary anthropology to interpret extreme self-sacrifice through the concept of identity fusion. The model neglects the role of normative systems in shaping behaviors, especially in relation to violent extremism. In peaceful groups, increasing fusion will actually decrease extremism. Groups collectively appraise threats and opportunities, actively debate action options, and rarely choose violence toward self or others.

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