scholarly journals Has the Earth been exposed to numerous supernovae within the last 300 kyr?

2014 ◽  
Vol 14 (3) ◽  
pp. 375-378 ◽  
Author(s):  
Adrian L. Melott ◽  
Ilya G. Usoskin ◽  
Gennady A. Kovaltsov ◽  
Claude M. Laird

AbstractFirestone (2014) asserted evidence for numerous (23) nearby (d < 300 pc) supernovae (SNe) within the Middle and Late Pleistocene. If true, this would have strong implications for the irradiation of the Earth; at this rate, the mass extinction level events due to SNe would be more frequent than 100 Myr. However, there are numerous errors in the application of past research. The paper overestimates likely nitrate and14C production from moderately nearby SNe by about four orders of magnitude. Moreover, the results are based on wrongly selected (obsolete) nitrate and14C datasets. The use of correct and up-to-date datasets does not confirm the claimed results. The claims in the paper are invalid.

Radiocarbon ◽  
1997 ◽  
Vol 39 (1) ◽  
pp. 27-32 ◽  
Author(s):  
John C. Vogel ◽  
Joel Kronfeld

Twenty paired 14C and U/Th dates covering most of the past 50,000 yr have been obtained on a stalagmite from the Cango Caves in South Africa as well as some additional age-pairs on two stalagmites from Tasmania that partially fill a gap between 7 ka and 17 ka ago. After allowance is made for the initial apparent 14C ages, the age-pairs between 7 ka and 20 ka show satisfactory agreement with the coral data of Bard et al. (1990, 1993). The results for the Cango stalagmite between 25 ka and 50 ka show the 14C dates to be substantially younger than the U/Th dates except at 49 ka and 29 ka, where near correspondence occurs. The discrepancies may be explained by variations in 14C production caused by changes in the magnetic dipole field of the Earth. A tentative calibration curve for this period is offered.


1968 ◽  
Vol 5 (6) ◽  
pp. 1467-1488 ◽  
Author(s):  
C. S. Churcher

Five ungulates are reported from gravels comprising the second major terrace above the Bow River's north bank at Cochrane, Alberta. These ungulates are Cervus canadensis (wapiti), Rangifer tarandus (caribou), Ovis canadensis (mountain sheep), Bison occidentalis (extinct western bison), and Equus conversidens (extinct Mexican ass). E. conversidens was previously known from middle and late Pleistocene beds of the southern United States and Mexico and is here reported from the post-Wisconsin Pleistocene of Alberta and possibly Saskatchewan. Radiocarbon analysis of Bison bones from the gravels yielded two dates that averaged 11 065 B.P.


2021 ◽  
Author(s):  
Ronald R. Gutierrez ◽  
Frank E. Escusa ◽  
Alice Lefebvre ◽  
Carlo Gualtieri ◽  
Francisco Nunez-Gonzalez ◽  
...  

&lt;p&gt;Open and data-driven paradigms have allowed to answer fundamental scientific questions in different disciplines such as astronomy, ecology and fluid mechanics, among others. Recently, the need to collaboratively build a large, engineered and freely accessible bed form database has been highlighted as a necessary step to adopt these paradigms in bed form dynamics research.&lt;/p&gt;&lt;p&gt;Most large database architectures have followed the principles of relational databases model solutions (RDBMS). Recently, non-relational (NoSQL) architectures (e.g., key-value store, graph databases, document-oriented, etc.) have been proposed to improve the capabilities and flexibility of RDBMS. Both RDBMS and NoSQL architectures require designing an engineered metadata structure to define the data taxonomy and structure, which are subsequently used to develop a metadata language for data querying. Past research suggests that the development of a metadata language needs a collaborative and iterative approach.&lt;/p&gt;&lt;p&gt;Defining the data taxonomy and structure for bed form data may be challenging because: [1] there is not a standardized protocol for conducting field and laboratory measurements; [2] it is expected that existing bed form data have a wide spectrum of data characteristics (e.g. length, format, resolution, structured or non-structured, etc.); and [3] bedforms are studied by scientists and engineers from different disciplines (e.g., geologists, ecologists, civil and water engineers, etc.).&lt;/p&gt;&lt;p&gt;In recent years, several data repositories have been built to manage large datasets related to the Earth System. One of these repositories is the Earth Science Information Partners, which has proposed standards to promote and improve the preservation, availability and overall quality of Earth System related data. These standards map the roles of participants (e.g., creators, intermediaries and end users) and delivers protocols to ensure proper data distribution and quality control.&lt;/p&gt;&lt;p&gt;This contribution presents the first iteration of a metadata language for subaqueous bed form data, named BedformsML0, which adopts the standards of the Earth Science Information Partners. BedformsML0 may serve as a prototype to describe bed form observations from field and laboratory measurements, model outputs, technical reports, scientific papers, post processed data, etc. Biogeoenvironmental observations associated to bed form dynamics (e.g., hydrodynamics, turbulence, river and coastal morphology, biota density, habitat metrics, sediment transport, sediment properties, land use dynamics, etc.) may also be represented in BedformsML0. It could subsequently be improved in future iterations via the collaboration of professionals from different Earth science fields to also describe subaerial, and extraterrestrial bed form data. Likewise, BedformsML0 can be used as machine search query selection for massive data processing and visualization of bed form observations.&amp;#160;&lt;/p&gt;


2019 ◽  
Vol 196 ◽  
pp. 102832 ◽  
Author(s):  
Per Möller ◽  
Ívar Örn Benediktsson ◽  
Johanna Anjar ◽  
Ole Bennike ◽  
Martin Bernhardson ◽  
...  

2017 ◽  
Vol 92 (2) ◽  
pp. 305-312 ◽  
Author(s):  
Fredrick K. Manthi ◽  
Francis H. Brown ◽  
Michael J. Plavcan ◽  
Lars Werdelin

AbstractThe partial skull of a lion from Natodomeri, northwest Kenya is described. The Natodomeri sites are correlated with Member I of the Kibish Formation, dated to between 195 ka and ca. 205 ka. The skull is remarkable for its very great size, equivalent to the largest cave lions (Panthera spelaea [Goldfuss, 1810]) of Pleistocene Eurasia and much larger than any previously known lion from Africa, living or fossil. We hypothesize that this individual represents a previously unknown population or subspecies of lion present in the late Middle and Late Pleistocene of eastern Africa rather than being an indication of climate-driven size increase in lions of that time. This raises questions regarding the extent of our understanding of the pattern and causes of lion evolution in the Late Pleistocene.


2020 ◽  
Vol 20 (2) ◽  
pp. 829-863 ◽  
Author(s):  
Adeyemi A. Adebiyi ◽  
Jasper F. Kok ◽  
Yang Wang ◽  
Akinori Ito ◽  
David A. Ridley ◽  
...  

Abstract. Mineral dust is the most abundant aerosol species by mass in the atmosphere, and it impacts global climate, biogeochemistry, and human health. Understanding these varied impacts on the Earth system requires accurate knowledge of dust abundance, size, and optical properties, and how they vary in space and time. However, current global models show substantial biases against measurements of these dust properties. For instance, recent studies suggest that atmospheric dust is substantially coarser and more aspherical than accounted for in models, leading to persistent biases in modelled impacts of dust on the Earth system. Here, we facilitate more accurate constraints on dust impacts by developing a new dataset: Dust Constraints from joint Observational-Modelling-experiMental analysis (DustCOMM). This dataset combines an ensemble of global model simulations with observational and experimental constraints on dust size distribution and shape to obtain more accurate constraints on three-dimensional (3-D) atmospheric dust properties than is possible from global model simulations alone. Specifically, we present annual and seasonal climatologies of the 3-D dust size distribution, 3-D dust mass extinction efficiency at 550 nm, and two-dimensional (2-D) atmospheric dust loading. Comparisons with independent measurements taken over several locations, heights, and seasons show that DustCOMM estimates consistently outperform conventional global model simulations. In particular, DustCOMM achieves a substantial reduction in the bias relative to measured dust size distributions in the 0.5–20 µm diameter range. Furthermore, DustCOMM reproduces measurements of dust mass extinction efficiency to almost within the experimental uncertainties, whereas global models generally overestimate the mass extinction efficiency. DustCOMM thus provides more accurate constraints on 3-D dust properties, and as such can be used to improve global models or serve as an alternative to global model simulations in constraining dust impacts on the Earth system.


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