Comment on the "Hypothesis for the role of toxin-producing algae in Phanerozoic mass extinctions based on evidence from the geologic record and modern environments" (Discussion)

2011 ◽  
Vol 18 (1) ◽  
pp. 55-57 ◽  
Author(s):  
Martin R. Smith
Keyword(s):  
Mass Extinctions ◽  
Geologic Record

THE ROLE OF GEOCHRONOLOGY IN LINKING FLOOD BASALTS TO MASS EXTINCTIONS

2018 ◽  
Author(s):  
Paul R. Renne ◽  
◽  
Benjamin A. Black ◽  
Benjamin A. Black ◽  
Isabel Fendley ◽  
...  
Keyword(s):  
Mass Extinctions ◽  
Flood Basalts

Crocodilian diversity in space and time: the role of climate in paleoecology and its implication for understanding K/T extinctions

Paleobiology ◽  
1998 ◽  
Vol 24 (4) ◽  
pp. 470-497 ◽  
Author(s):  
Paul J. Markwick
Keyword(s):  
Northern Hemisphere ◽  
Middle Eocene ◽  
Temporal Trends ◽  
Late Eocene ◽  
High Rate ◽  
Mass Extinctions ◽  
Crown Group ◽  
Climatic Effects ◽  
General Decline

The taxonomic diversity of crocodilians (Crocodylia) through the last 100 million years shows a general decline in the number of genera and species to the present day. But this masks a more complex pattern. This is investigated here using a comprehensive database of fossil crocodilians that provides the opportunity to examine spatial and temporal trends, the influence of sampling, and the role of climate in regulating biodiversity.Crown-group crocodilians, comprising the extant families Alligatoridae, Crocodylidae, and Gavialidae, show the following trend: an initial exponential diversification through the Late Cretaceous and Paleocene that is restricted to the Northern Hemisphere until after the K/T boundary; relatively constant diversity from the Paleocene into the middle Eocene that may be an artifact of sampling, which might mask an actual decline in numbers; low diversity during the late Eocene and Oligocene; a second exponential diversification during the Miocene and leveling off in the late Miocene and Pliocene; and a precipitous drop in the Pleistocene and Recent. The coincidence of drops in diversity with global cooling is suggestive of a causal link—during the initial glaciation of Antarctica in the Eocene and Oligocene and the Northern Hemisphere glaciation at the end of the Pliocene. However, matters are complicated in the Northern Hemisphere by the climatic effects of regional uplift.Although the global trend of diversification is unperturbed at the K/T boundary, this is largely due to the exceptionally high rate of origination in the early Paleocene. Nonetheless, the survival of such a demonstrably climate-sensitive group strongly suggests that a climatic explanation for the K/T mass extinctions, especially the demise of the dinosaurs, must be reconsidered.

scholarly journals Role of microorganisms in the production of lime mud and implications for interpretation of ancient micrite deposits

1992 ◽  
Vol 6 ◽  
pp. 248-248
Author(s):  
L.L. Robbins ◽  
K. Yates
Keyword(s):  
Calcium Carbonate ◽  
Green Algae ◽  
Close Association ◽  
Carbonate Platforms ◽  
Blue Green Algae ◽  
Marine Deposits ◽  
Lime Mud ◽  
Transmission Electron ◽  
Geologic Record

Geologists have long been plagued by the lack of evidence for the origin of ancient micrite deposits: any paleontological evidence is typically obscured or lacking altogether. The role of modern marine picoplankton gives insight into the origin of one mode of lime mud formation and may aid in the interpretation of ancient marine deposits.Whitings, patches of floating lime mud in supersaturated seawater on carbonate platforms, obtained from the Bahama Bank were analyzed utilizing biochemical techniques and Transmission Electron Microscopy. All Whitings indicated a close association between picoplankton cellular material and calcium carbonate crystals. Culture experiments indicated the presence of at least ten different picoplankton species in Whitings water. Two major genera found were the blue-green algae, Synechococcus and Synechocystis. Field and laboratory experimental data indicated that these cells and cellular organics play a major role in Whitings formation. The cells may undergo epicellular precipitation of calcium carbonate induced by photosynthesis. Environmental conditions necessary for this process have been delineated through field data and laboratory experiments.While picoplankton organics are rarely preserved over geologic time, the product of their life habit, namely lime mud, is preserved as micrite. Thick occurrences of micrite deposited in marine environments are widespread throughout the geologic record, ranging in age from Precambrian to Recent. Although rare, fossilized blue-green algae have been observed in Archean rocks and may be the only evidence that implicates these organisms in lime mud formation. The Whitings phenomenon serves as an excellent example in which a specific type of organism may be a prolific contributor to the rock record, and yet leaves no direct paleontological evidence of its involvement.

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.

scholarly journals Evolutionary catastrophes and the Goldilocks problem

2007 ◽  
Vol 6 (4) ◽  
pp. 325-329 ◽  
Author(s):  
Milan M. Ćirković
Keyword(s):  
Rare Earth ◽  
Milky Way ◽  
Human Life ◽  
Biological Evolution ◽  
Selection Effects ◽  
Mass Extinctions ◽  
Terrestrial Biosphere ◽  
Habitable Planet ◽  
Observation Selection

AbstractOne of the mainstays of the controversial ‘rare Earth’ hypothesis is the ‘Goldilocks problem’ regarding various parameters describing a habitable planet, partially involving the role of mass extinctions and other catastrophic processes in biological evolution. Usually, this is construed as support for the uniqueness of the Earth's biosphere and intelligent human life. Here it is argued that this is a misconstrual and that, on the contrary, observation-selection effects when applied to catastrophic processes make it very difficult for us to discern whether the terrestrial biosphere and evolutionary processes which created it are exceptional in the Milky Way or not. This agnosticism, in turn, supports the validity and significance of practical astrobiological and SETI research.

scholarly journals The important role of private wildlife organisations in facilitating scientific research: A case study of the Australian Dingo Foundation

2020 ◽  
Author(s):  
Bradley P. Smith ◽  
Shennai G. Palermo ◽  
Lyn Watson
Keyword(s):  
Captive Breeding ◽  
Scientific Literature ◽  
Mass Extinctions ◽  
The Past ◽  
Lethal Management ◽  
Conducting Research ◽  
Free Ranging ◽  
Private Organisation

As we enter an era of global mass extinctions, it is important to tackle wildlife research and conservation from multiple fronts, including those made available by wildlife organisations, zoos and sanctuaries. Captive studies are particularly useful when studying free-ranging populations is difficult, and/or when controlled conditions are required. Yet, despite the significant role that they play in supporting research and conservation of species and ecosystems, they are rarely recognised in the scientific literature. Here we present a case study of the Australian Dingo Foundation (ADF), a private organisation and captive breeding facility that actively supports research and conservation efforts relating to the dingo ( Canis dingo). Over the past decade (2010 to 2020), the ADF has facilitated research across eight research disciplines that include archaeology, behaviour, biology, cognition, evolutionary psychology, non-lethal management, reproduction and parental behaviour, and vocalisations. This has resulted in at least 21 published scientific studies which are summarised in this paper. As this case study demonstrates, captive facilities have the potential to contribute to the understanding and conservation of dingoes by providing practical alternatives to, and/or supplement studies of free-ranging populations. We conclude by outlining some of the implications and limitations of conducting research using captive dingo populations.

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