Large-body impact: the least unlikely cause of pulsed extinction

1992 ◽  
Vol 6 ◽  
pp. 240-240
Author(s):  
David M. Raup
Keyword(s):  
Short Interval ◽  
Large Body ◽  
Temporal Distribution ◽  
Radiometric Dating ◽  
Mass Extinctions ◽  
Widespread Species ◽  
Chance Coincidence ◽  
Asteroid Impact ◽  
The Past ◽  
Independent Events

In the past year, a strong consensus in the geological community has developed in favor of comet or asteroid impact as the ultimate cause of the K-T mass extinction, although many paleontologists remain doubtful. The discovery of tektites and craters with argon-argon ages matching the K-T boundary has finally removed the “smoking gun” problem. It is important, therefore, to evaluate large-body impact as a possible cause of other Phanerozoic extinctions, and to do so as carefully as possible before enthusiasm for the K-T success overwhelms objectivity in this research area.Approximately 60% of all species extinctions in the Phanerozoic occurred in “pulsed” extinctions, defined as ecologically and geographically pervasive episodes in which the number of species going extinct in a geologically short interval far exceeds any reasonable estimate based on chance coincidence of independent events. In addition to the well-known mass extinctions, pulsed extinctions often mark system, series, and stage boundaries, and probably some zonal boundaries.To be plausible, any proposed cause of pulsed extinctions must be (1) geographically pervasive (regional or global), (2) effective in diverse habitats, and (3) relatively quick-acting (to inhibit survival of species by migration or adaptation). The stresses causing the extinctions must be sufficiently severe and rare to be beyond the reach of natural selection, so that species do not have prior opportunity to evolve defenses.These requirements severely limit the possibilities to phenomena that occur on time scales of one million to tens of millions of years, far longer than the tens or hundreds of years available for study by traditional actualistic approaches. In view of the Phanerozoic record, it is not surprising that the earth has not experienced a pulsed extinction in historic times (excluding human influences). This suggests that extinction is one case where the present is a not the key to the past, and a full exploration of the problem will require a substantial re-ordering of thinking.Furthermore, because pulsed extinctions involve geographically widespread species (as well as restricted taxa), and because extinction of widespread species may be qualitatively different from that of local endemics, the common extrapolation from studies of extinction in local populations is risky.Of the many phenomena suggested as causes of pulsed extinction, large-body impact is the one that most nearly satisfies the requirements, and is therefore the least unlikely of the candidates. Temporal distribution is especially critical. Currently accepted flux estimates for comet and asteroid impacts are in the appropriate frequency range to explain the extinction record, but testing the hypothesis will depend on better radiometric dating of the 100+ craters and other confirmed impact events.

Extinction from a paleontological perspective

1993 ◽  
Vol 1 (3) ◽  
pp. 207-216 ◽  
Author(s):  
David M. Raup
Keyword(s):  
Mass Extinction ◽  
Fossil Record ◽  
Mass Extinctions ◽  
Evolutionary Time ◽  
Widespread Species ◽  
Chance Coincidence ◽  
Independent Events

Extinction of widespread species is common in evolutionary time (millions of years) but rare in ecological time (hundreds or thousands of years). In the fossil record, there appears to be a smooth continuum between background and mass extinction; and the clustering of extinctions at mass extinctions cannot be explained by the chance coincidence of independent events. Although some extinction is selective, much is apparently random in that survivors have no recognizable superiority over victims. Extinction certainly plays an important role in evolution, but whether it is constructive or destructive has not yet been determined.

scholarly journals Bioinsecticides based on plant essential oils: a short overview

2020 ◽  
Vol 75 (7-8) ◽  
pp. 179-182
Author(s):  
Murray B. Isman
Keyword(s):  
Essential Oils ◽  
Crop Protection ◽  
Large Body ◽  
Regulatory Agencies ◽  
The European Union ◽  
Plant Essential Oils ◽  
The Past ◽  
Wide Range ◽  
The Usa ◽  
Regulatory Challenges

AbstractInterest in the discovery and development of plant essential oils for use as bioinsecticides has grown enormously in the past 20 years. However, successful commercialization and utilization of crop protection products based on essential oils has thus far lagged far behind their promise based on this large body of research, most notably because with the exceptions of the USA and Australia, such products receive no special status from regulatory agencies that approve new pesticides for use. Essential oil-based insecticides have now been used in the USA for well over a decade, and more recently have seen use in the European Union (EU), Korea, and about a dozen other countries, with demonstrated efficacy against a wide range of pests and in numerous crop systems. For the most part these products are based on commodity essential oils developed as flavor and fragrance agents for the food and cosmetic industries, as there are formidable logistic, economic, and regulatory challenges to the use of many other essential oils that otherwise possess potentially useful bioactivity against pests. In spite of these limitations, the overall prospects for biopesticides, including those based on essential oils, are encouraging as the demand for sustainably-produced and/or organic food continues to increase worldwide.

Mathematical Issues Arising From the Directed Mutation Controversy

Genetics ◽  
2003 ◽  
Vol 164 (1) ◽  
pp. 373-379
Author(s):  
Qi Zheng
Keyword(s):  
Mathematical Reasoning ◽  
Large Body ◽  
Directed Mutation ◽  
The Past ◽  
New Evidence

Abstract During the past 14 years or so a large body of new evidence that supposedly supports the directed mutation hypothesis has accumulated. Interpretation of some of the evidence depends on mathematical reasoning, which can be subtler than it appears at first sight. This article attempts to clarify some of the mathematical issues arising from the directed mutation controversy, thereby offering alternative interpretations of some of the evidence.

scholarly journals ANALYSIS OF THE SPATIOTEMPORAL CHARACTERISTICS OF HEMORRHAGIC FEVER WITH RENAL SYNDROME IN HUBEI PROVINCE, CHINA

2015 ◽  
Vol II-4/W2 ◽  
pp. 207-210
Author(s):  
H. Fan ◽  
L. Ge ◽  
L. Song ◽  
Q. Zhao
Keyword(s):  
Prevention And Control ◽  
Temporal Distribution ◽  
Hemorrhagic Fever ◽  
Spatiotemporal Analysis ◽  
Systematic Investigation ◽  
Hubei Province ◽  
Spatial And Temporal Distribution ◽  
The Past ◽  
Comprehensive Examination ◽  
And Control

Hemorrhagic fever with renal syndrome(HFRS) is a worldwide fulminant infectious disease. Since the first HFRS cases in Hubei Province were reported in 1957, the disease has spread across the province and Hubei has become one of seriously affected areas in China. However, the epidemic characteristics of HFRS are still not entirely clear. Therefore, a systematic investigation of spatial and temporal distribution pattern of HFRS system is needed. In order to facilitate better prevention and control of HFRS in Hubei Province, in this paper, a GIS spatiotemporal analysis and modeling tool was developed to analyze the spatiotemporal dynamics of the HFRS epidemic, as well as providinga comprehensive examination the dynamic pattern of HFRS in Hubei over the past 30 years (1980-2009), to determine spatiotemporal change trends and the causes of HFRS. This paper describes the experiments and their results.

scholarly journals Collinder 135 and UBC 7: A physical pair of open clusters

2020 ◽  
Vol 642 ◽  
pp. L4
Author(s):  
Dana A. Kovaleva ◽  
Marina Ishchenko ◽  
Ekaterina Postnikova ◽  
Peter Berczik ◽  
Anatoly E. Piskunov ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Observational Evidence ◽  
Open Clusters ◽  
Line Of Sight ◽  
Kinematic Parameters ◽  
Current Line ◽  
Chance Coincidence ◽  
The Past ◽  
Link Type ◽  
Spatial Coordinates

Context. Given the closeness of the two open clusters Collinder 135 and UBC 7 on the sky, we investigate the possibility that the two clusters are physically related. Aims. We aim to recover the present-day stellar membership in the open clusters Cr 135 and UBC 7 (300 pc from the Sun) in order to constrain their kinematic parameters, ages, and masses and to restore their primordial phase space configuration. Methods. The most reliable cluster members are selected with our traditional method modified for the use of Gaia DR2 data. Numerical simulations use the integration of cluster trajectories backwards in time with our original high-order Hermite4 code φ−GRAPE. Results. We constrain the age, spatial coordinates, velocities, radii, and masses of the clusters. We estimate the actual separation of the cluster centres equal to 24 pc. The orbital integration shows that the clusters were much closer in the past if their current line-of-sight velocities are very similar and the total mass is more than seven times larger than the mass of the most reliable members. Conclusions. We conclude that the two clusters Cr 135 and UBC 7 might very well have formed a physical pair based on the observational evidence as well as numerical simulations. The probability of a chance coincidence is only about 2%.

Paleobiogeographical extinction patterns of Permian brachiopods in the Asian–western Pacific region

Paleobiology ◽  
2002 ◽  
Vol 28 (4) ◽  
pp. 449-463 ◽  
Author(s):  
Shen Shu-Zhong ◽  
G. R. Shi
Keyword(s):  
Biological Diversity ◽  
Short Interval ◽  
Temporal Variations ◽  
Western Pacific ◽  
Pacific Region ◽  
Mass Extinctions ◽  
Western Pacific Region ◽  
Southern Tibet ◽  
Triassic Boundary ◽  
Rarefaction Analysis

Spatial and temporal variations in biological diversity are critical in understanding the role of biogeographical regulation (if any) on mass extinctions. An analysis based on a latest database of the stratigraphic ranges of 89 Permian brachiopod families, 422 genera, and 2059 species within the Boreal, Paleoequatorial, and Gondwanan Realms in the Asian–western Pacific region suggests two discrete mass extinctions, each possibly with different causes. Using species/family rarefaction analysis, we constructed diversity curves for late Artinskian–Kungurian, Roadian–Wordian, Capitanian, and Wuchiapingian intervals for filtering out uneven sampling intensities. The end-Changhsingian (latest Permian) extinction eliminated 87–90% of genera and 94–96% of species of Brachiopoda. The timing of the end-Changhsingian extinction of brachiopods in the carbonate settings of South China and southern Tibet indicates that brachiopods suffered a rapid extinction within a short interval just below the Permian/Triassic boundary.In comparison, the end-Guadalupian/late Guadalupian extinction is less profound and varies temporally in different realms. Brachiopods in the western Pacific sector of the Boreal Realm nearly disappeared by the end-Guadalupian but experienced a relatively long-term press extinction spanning the entire Guadalupian in the Gondwanan Realm. The end-Guadalupian brachiopod diversity fall is not well reflected at the timescale used here in the Paleoequatorial Realm because the life-depleted early Wuchiapingian was overlapped by a rapid radiation phase in the late Wuchiapingian. The Guadalupian fall appears to be related to the dramatic reduction of habitat area for the brachiopods, which itself is associated with the withdrawal of seawater from continental Pangea and the closure of the Sino-Mongolian seaway by the end-Guadalupian.

Broadscale evaluation of the sedimentary Hg proxy for volcanism – insights from data compilation

2021 ◽  
Author(s):  
Joost Frieling ◽  
Isabel Fendley ◽  
Tamsin Mather
Keyword(s):  
Environmental Factors ◽  
Volcanic Activity ◽  
Sediment Chemistry ◽  
High Temporal Resolution ◽  
Gaseous Emissions ◽  
Mass Extinctions ◽  
Volcanic Emissions ◽  
Deep Time ◽  
The Past ◽  
Data Compilation

<p>Over the past few years, mercury (Hg) concentrations in (predominantly) marine sediments have gained widespread attention as a far-field, high-temporal resolution proxy for deep-time enhanced volcanic activity. The primary focus of these Hg studies has been a range of events in the past 500 million years; mostly larger and smaller mass extinctions and periods of high-amplitude climate change. As a result, sedimentary Hg data reinforced the notion many of these events are indeed coeval with and hypothesized causally connected to large igneous provinces (LIPs). </p><p>However, relatively poor constraints on long-term dispersal of emissions through the marine and terrestrial biosphere, accumulation and preservation mechanisms of Hg pose difficulties for its use as a qualitative proxy for enhanced volcanic emissions. As a result, using sedimentary Hg for detailed modeling of Hg cycling or past gaseous emissions of magmatic volatiles, e.g. carbon and sulfur, and by extension environmental impact, remains speculative.</p><p>The use of Hg normalization to common Hg-binding sedimentary components such as organic carbon (TOC), Fe or Al provides a basic means of comparing relative Hg loading within a sedimentary sequence. Yet, normalizing Hg to these major sedimentary components relies on simple linear relations and this approach often leaves substantial variance. While the high Hg concentrations have usually been ascribed to variability in volcanic activity, there are likely other factors that may invoke changes in the Hg concentrations in sediments, or mask Hg emitted by volcanism such as amount or type and flux of organic matter being deposited in basins and oxygenation of water and local sediments.</p><p>To evaluate potential confounding factors, we compiled published Hg, TOC and bulk and trace element data, modern and deep-time events, periods with and without known anomalous volcanic activity and cover a range of depositional settings. We find that the depositional setting, as inferred from lithology and bulk sediment chemistry exerts a major control on the overall concentrations of Hg. Differences in Hg loading between time-correlative deposits persist after normalization to major sedimentary components, likely as a result of a complex interplay between various spatial and environmental factors. Our data compilation further allows us to explore the potential of establishing a range for background Hg values and variability through different periods of geological deep-time. Collectively, such constraints can aid the understanding of changes induced by environmental factors or volcanic emissions and inform Hg-cycling models.</p>

A Monumental Horse Burial in the Armenian Highlands

2021 ◽  
Vol 49 (3) ◽  
pp. 41-50
Author(s):  
A. Nachmias ◽  
G. Bar-Oz ◽  
D. Nadel ◽  
I. Petrosyan ◽  
B. Gasparyan
Keyword(s):  
Morphological Characteristics ◽  
Radiometric Dating ◽  
Large Individual ◽  
Metal Ring ◽  
Tall Stature ◽  
Unique Combination ◽  
The Past

Here we report on the unprecedented discovery of the complete skeleton of a ritually interred adult stallion with a bronze ring in its mouth. The horse was buried in a unique 15-meters diameter monumental stone-built tomb excavated in the Aghavnatun necropolis located on the southern slopes of Mt. Aragats, in the northern fringes of the Ararat Depression, Republic of Armenia. The tumulus was roughly circular; the horse’s remains were found in situ, in an inner oval-shaped structure. Our methodological procedure included a detailed description of the burial, a taphonomic study of the bones, and meticulous morphometric observations and measurements, and thus we could provide a taxonomic defi nition and an age estimate. Direct radiometric dating of the horse’s skeleton provided a date of 2130±20 BP. The morphological characteristics of the horse, with its tall stature and slender feet, suggest that it was a large individual, similar to the extinct breed of Nisean horse previously known mainly from textual and iconographical sources. The metal ring found in the mouth of the horse suggests that it likely served as a breeding stallion. This discovery presents a unique combination of zooarchaeological evidence for the importance of the horse in the Parthian-Hellenistic worlds, and advances our understanding of the broad social signifi cance of the past breeding of equids in the Armenian Highlands.

OH Emission from Protostars

1970 ◽  
Vol 1 (7) ◽  
pp. 336-337
Author(s):  
I. D. Johnston
Keyword(s):  
Large Body ◽  
Class I ◽  
Emission Sources ◽  
Equilibrium Situation ◽  
The Past ◽  
Maser Action ◽  
Non Equilibrium

There is a large body of evidence to suggest that the anomalous OH emission sources—particularly those which are classified as class I sources—are associated with protostars. It is also known, from the theories brought forward over the past four years, that maser action can be caused by quite a variety of non-equilibrium situations. It is argued here that one particular kind of non-equilibrium situation which can plausibly be expected to exist in protostars is very similar to that proposed previously in the electron-pumping model, and that, in this new context, it can mimic most of the observed features of class I sources.

‘We have long memories in this area’: Ulster Defence Regiment place-memory along the Irish border

2020 ◽  
pp. 175069802092145
Author(s):  
Joseph S Robinson
Keyword(s):  
Northern Ireland ◽  
Political Violence ◽  
Transitional Justice ◽  
Political Change ◽  
Large Body ◽  
Political Space ◽  
The Past ◽  
Place Memory ◽  
Post Conflict ◽  
Time Away

A large body of literature assumes post-conflict societies can and should mediate public memory towards frames conducive to a reconciled future. However, this article argues that such a drive marginalises survivors of political violence who narrate the past as still-present wounds. The linear temporality of transitional justice presumes an idealised trajectory through time, away from violence and towards reconciliation. However, this idealised temporality renders anachronistic survivors who depend on the prolongation of traumatic pasts for the possibility of political change. Using the case of former Ulster Defence Regiment in Northern Ireland, this article examines this prolongation through the lens of Ulster Defence Regiment survivors’ resistant place-memory along the Southwest run of the Irish border. Through the performative retemporalisation of everyday places and landscapes, survivors demand that their resistant memories and narrative frames of past violence still belong and still have active political resonance in transitional political space.

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