scholarly journals Causes of global extinctions in the history of life: facts and hypotheses

2020 ◽  
Vol 24 (4) ◽  
pp. 407-419
Author(s):  
T. M. Khlebodarova ◽  
V. A. Likhoshvai
Keyword(s):  
Fossil Record ◽  
Complex Dynamics ◽  
Life Forms ◽  
Marine Biota ◽  
Mass Extinctions ◽  
Short Period ◽  
Common Opinion ◽  
Systematized Review ◽  
The Moment ◽  
Life On Earth

Paleontologists define global extinctions on Earth as a loss of about three-quarters of plant and animal species over a relatively short period of time. At least five global extinctions are documented in the Phanerozoic fossil record (~500-million-year period): ~65, 200, 260, 380, and 440 million years ago. In addition, there is evidence of global extinctions in earlier periods of life on Earth – during the Late Cambrian (~500 million years ago) and Ediacaran periods (more than 540 million years ago). There is still no common opinion on the causes of their occurrence. The current study is a systematized review of the data on recorded extinctions of complex life forms on Earth from the moment of their occurrence during the Ediacaran period to the modern period. The review discusses possible causes for mass extinctions in the light of the influence of abiogenic factors, planetary or astronomical, and the consequences of their actions. We evaluate the pros and cons of the hypothesis on the presence of periodicity in the extinction of Phanerozoic marine biota. Strong evidence that allows us to hypothesize that additional mechanisms associated with various internal biotic factors are responsible for the emergence of extinctions in the evolution of complex life forms is discussed. Developing the idea of the internal causes of periodicity and discontinuity in evolution, we propose our own original hypothesis, according to which the bistability phenomenon underlies the complex dynamics of the biota development, which is manifested in the form of global extinctions. The bistability phenomenon arises only in ecosystems with predominant sexual reproduction. Our hypothesis suggests that even in the absence of global abiotic catastrophes, extinctions of biota would occur anyway. However, our hypothesis does not exclude the possibility that in different periods of the Earth’s history the biota was subjected to powerful external influences that had a significant impact on its further development, which is reflected in the Earth’s fossil record.

scholarly journals Jupiter – friend or foe? II: the Centaurs

2008 ◽  
Vol 8 (2) ◽  
pp. 75-80 ◽  
Author(s):  
J. Horner ◽  
B.W. Jones
Keyword(s):  
Solar System ◽  
Kuiper Belt ◽  
Giant Planet ◽  
Mass Extinctions ◽  
The Earth ◽  
Impact Rate ◽  
Short Period ◽  
Impact Risk ◽  
Life On Earth ◽  
The Impact

AbstractIt has long been assumed that the planet Jupiter acts as a giant shield, significantly lowering the impact rate of minor bodies upon the Earth, and thus enabling the development and evolution of life in a collisional environment which is not overly hostile. In other words, it is thought that, thanks to Jupiter, mass extinctions have been sufficiently infrequent that the biosphere has been able to diversify and prosper. However, in the past, little work has been carried out to examine the validity of this idea. In the second of a series of papers, we examine the degree to which the impact risk resulting from objects on Centaur-like orbits is affected by the presence of a giant planet, in an attempt to fully understand the impact regime under which life on Earth has developed. The Centaurs are a population of ice-rich bodies which move on dynamically unstable orbits in the outer Solar system. The largest Centaurs known are several hundred kilometres in diameter, and it is certain that a great number of kilometre or sub-kilometre sized Centaurs still await discovery. These objects move on orbits which bring them closer to the Sun than Neptune, although they remain beyond the orbit of Jupiter at all times, and have their origins in the vast reservoir of debris known as the Edgeworth–Kuiper belt that extends beyond Neptune. Over time, the giant planets perturb the Centaurs, sending a significant fraction into the inner Solar System where they become visible as short-period comets. In this work, we obtain results which show that the presence of a giant planet can act to significantly change the impact rate of short-period comets on the Earth, and that such planets often actually increase the impact flux greatly over that which would be expected were a giant planet not present.

Interpretation of significant ground-response and structure strong motions recorded during the 1994 Northridge earthquake

1996 ◽  
Vol 86 (1B) ◽  
pp. S231-S246 ◽  
Author(s):  
A. F. Shakal ◽  
M. J. Huang ◽  
R. B. Darragh
Keyword(s):  
Flexible Structures ◽  
Northridge Earthquake ◽  
Moment Frame ◽  
Ground Response ◽  
Short Period ◽  
Frame Buildings ◽  
Story Drift ◽  
San Fernando ◽  
San Fernando Valley ◽  
The Moment

Abstract Some of the largest accelerations and velocities ever recorded at ground-response and structural sites occurred during the Northridge earthquake. These motions are greater than most existing attenuation models would have predicted. Although the motions are large, the correspondence between measured acceleration and damage requires further study, since some sites with high acceleration experienced only moderate damage. Also, some peak vertical accelerations were larger than the horizontal, but in general, they are smaller and fit the pattern observed in previous earthquakes. Strong-motion records processed to date show significant differences in acceleration and velocity waveforms and amplitudes across the San Fernando Valley. Analysis of processed data from several buildings in the San Fernando Valley indicates that short-period buildings such as shear-wall buildings experienced large forces and relatively low inter-story drift during the Northridge earthquake. However, long-period (1 to 5 sec) steel or concrete moment-frame buildings experienced large inter-story drift. For this earthquake, accelerations did not always amplify from base to roof for flexible structures like the moment-frame buildings, but the displacements were always larger at the roof. The drifts at many of the moment-frame buildings were larger than the drift limit for working stress design in the building code. The records from a base-isolated building indicate that high-frequency motion was reduced significantly by the isolators. The isolators deformed about 3.5 cm, which is much less than the design displacement. The records from a parking structure show important features of the seismic response of this class of structure.

scholarly journals Novel water source for endolithic life in the hyperarid core of the Atacama Desert

2012 ◽  
Vol 9 (6) ◽  
pp. 2275-2286 ◽  
Author(s):  
J. Wierzchos ◽  
A. F. Davila ◽  
I. M. Sánchez-Almazo ◽  
M. Hajnos ◽  
R. Swieboda ◽  
...  
Keyword(s):  
Liquid Water ◽  
Capillary Condensation ◽  
Extreme Environments ◽  
Atacama Desert ◽  
Water Source ◽  
Life Forms ◽  
Alternative Source ◽  
Biological Adaptation ◽  
Salt Flats ◽  
Life On Earth

Abstract. The hyperarid core of the Atacama Desert, Chile, is possibly the driest and most life-limited place on Earth, yet endolithic microorganisms thrive inside halite pinnacles that are part of ancient salt flats. The existence of this microbial community in an environment that excludes any other life forms suggests biological adaptation to high salinity and desiccation stress, and indicates an alternative source of water for life other than rainfall, fog or dew. Here, we show that halite endoliths obtain liquid water through spontaneous capillary condensation at relative humidity (RH) much lower than the deliquescence RH of NaCl. We describe how this condensation could occur inside nano-pores smaller than 100 nm, in a newly characterized halite phase that is intimately associated with the endolithic aggregates. This nano-porous phase helps retain liquid water for long periods of time by preventing its evaporation even in conditions of utmost dryness. Our results explain how life has colonized and adapted to one of the most extreme environments on our planet, expanding the water activity envelope for life on Earth, and broadening the spectrum of possible habitats for life beyond our planet.

scholarly journals Russia – China: A Difficult Way to Strategic Partnership (To the 70th Anniversary of the Establishment of Diplomatic Relations)

2021 ◽  
pp. 231-245
Author(s):  
Sergey Biryukov ◽  
Keyword(s):  
Political Development ◽  
Complex Dynamics ◽  
World Order ◽  
Strategic Partnership ◽  
General Situation ◽  
Republic Of China ◽  
Bilateral Relations ◽  
Political Analysis ◽  
The Difference ◽  
The Moment

Introduction. The article is devoted to the features and historical evolution of the SovietChinese (later Russian-Chinese) relations from the moment of the proclamation of the People’s Republic of China in 1949 to the present. The analysis of the complex of factors that determined the complex dynamics of the relations between the two countries was carried out by the author of the article. It is shown that the SovietChinese (later – Russian-Chinese) relations developed from close alliance to alienation and confrontation – with reaching a level of strategic partnership in the second decade of the 21st century. Methods and materials. The authors seek a combination of general theoretical and special methods, focusing on the historical, sociocultural and political analysis. They are based on the analysis of periodicals, as well as using books, articles and materials of researchers on the problems of the political development of China and the USSR (Russia) and on the transformation of the nature of their bilateral relations. The author analyzes the current situation in the relations between the two countries, according to which the nature of the development of the general situation in international relations and the objective foreign policy interests of China and Russia encourage them to build and deepen bilateral partnership. Results. According to the author, many of the reasons that gave rise to a conflict of interests and confrontation between the two countries in previous years are exhausted today. At the same time, the joint participation of China and Russia in the formation and adoption of a new, more equitable and sustainable world order, in the settlement of conflicts and crises, in the arrangement of the Greater Eurasia space seems to the author justified and promising. Among the factors defining the nature of the Sino-Soviet relations the author identifies the relationship between the leaders of the two countries, the difference of geopolitical concepts and approaches, ideological disputes and differences in the views on strategy and prospects of the communist movement, the logic of the socio-political and socio-economic development in the context of modernization. The changing and contradictory correlation of these factors determined the development of the Soviet-Chinese (later Russian-Chinese) relations from a close alliance to mutual distancing and confrontation – with the subsequent entry into strategic partnership.

scholarly journals How important risk analysis of plastic pollution in coastal area? Case study in Masohi, Central Maluku

2020 ◽  
Vol 200 ◽  
pp. 02014
Author(s):  
Bachtiar W Mutaqin ◽  
Muh Aris Marfai ◽  
Muhammad Helmi ◽  
Nurhadi Nurhadi ◽  
Muhammad Rizali Umarella ◽  
...  
Keyword(s):  
Public Awareness ◽  
Coastal Areas ◽  
Plastic Waste ◽  
Small Island ◽  
Marine Biota ◽  
Plastic Pollution ◽  
Short Period ◽  
Almost All ◽  
And Function ◽  
Interdisciplinary Study

Human pressure on the coastal and aquatic surrounding ecosystem in Indonesia, through plastic waste, is increasing, considering that 60 % of the approximately 250 million people live in the coastal areas. Plastic waste originating from human activities has become a massive problem in almost all the small island and coastal regions, especially in the eastern part of Indonesia. This condition is caused by poor waste management and a lack of public awareness in disposing of waste in its place, including in an area known as its marine biodiversities and marine tourism spots like Masohi in Central Maluku. Also, the composition of waste is dominated by plastic waste that cannot be decomposed in a short period, continue circulated on the ocean currents, and will be deposited in coastal areas. Furthermore, some plastic waste will break down into micro-plastics that pollute not only the environment but also marine biota, which are often consumed by humans. This situation profoundly affects the sustainability and function of aquaecosystem services in coastal areas. Therefore, a comprehensive policy and regulation, and interdisciplinary study for analysing vulnerable coastal ecosystem, and mitigating the potential risk of plastic pollution in Masohi, Central Maluku are essential to be conducted.

scholarly journals From cosmos to intelligent life: the four ages of astrobiology

2012 ◽  
Vol 11 (4) ◽  
pp. 345-350 ◽  
Author(s):  
Marcelo Gleiser
Keyword(s):  
Chemical Elements ◽  
Life Forms ◽  
Big Bang ◽  
Self Awareness ◽  
First Stars ◽  
History Of ◽  
Life On Earth ◽  
The Big Bang ◽  
The Universe ◽  
Intelligent Life

AbstractThe history of life on Earth and in other potential life-bearing planetary platforms is deeply linked to the history of the Universe. Since life, as we know, relies on chemical elements forged in dying heavy stars, the Universe needs to be old enough for stars to form and evolve. The current cosmological theory indicates that the Universe is 13.7 ± 0.13 billion years old and that the first stars formed hundreds of millions of years after the Big Bang. At least some stars formed with stable planetary systems wherein a set of biochemical reactions leading to life could have taken place. In this paper, I argue that we can divide cosmological history into four ages, from the Big Bang to intelligent life. The physical age describes the origin of the Universe, of matter, of cosmic nucleosynthesis, as well as the formation of the first stars and Galaxies. The chemical age began when heavy stars provided the raw ingredients for life through stellar nucleosynthesis and describes how heavier chemical elements collected in nascent planets and Moons gave rise to prebiotic biomolecules. The biological age describes the origin of early life, its evolution through Darwinian natural selection and the emergence of complex multicellular life forms. Finally, the cognitive age describes how complex life evolved into intelligent life capable of self-awareness and of developing technology through the directed manipulation of energy and materials. I conclude discussing whether we are the rule or the exception.

scholarly journals The Delta Scuti Network: Steps Towards Successful Asteroseismology of Delta Scuti Stars

2002 ◽  
Vol 185 ◽  
pp. 598-599
Author(s):  
W. Zima ◽  
M. Breger ◽  
K. Bischof ◽  
F. Rodler ◽  
A. Stankov ◽  
...  
Keyword(s):  
High Precision ◽  
Main Sequence ◽  
Scientific Research ◽  
Mode Identification ◽  
Short Period ◽  
Delta Scuti ◽  
The Moment ◽  
Identification Techniques ◽  
Scuti Stars ◽  
Nonradial Oscillations

AbstractThe Delta Scuti Network (DSN) is a collaboration of astronomers all around the globe who study and observe short-period variables. The field of scientific research includes high-precision photometric and Spectroscopic global campaigns, mode identification techniques, and asteroseismological pulsation modeling. We present results for three stars that are receiving the most attention at the moment: 4 CVn, BI CMi, and 44 Tau. Our results demonstrate that a large number of simultaneously excited nonradial oscillations in stars on and above the main sequence can be detected by conventional means.

Reefs as the Centralizing Theme in an Undergraduate Invertebrate Paleontology Course

2012 ◽  
Vol 12 ◽  
pp. 21-42
Author(s):  
Constance M. Soja
Keyword(s):  
Fossil Record ◽  
Evolutionary History ◽  
Marine Invertebrate ◽  
Scientific Information ◽  
Field Trip ◽  
Mass Extinctions ◽  
Paleontological Data ◽  
San Salvador ◽  
Invertebrate Paleontology ◽  
The Impact

This course is designed so that topics in invertebrate paleontology are discussed in the context of reefs and their change through time. The goal is to help undergraduate students connect modern conservation issues with an enlightened appreciation of the fossil record. Using reefs as the centralizing theme of the course allows key concepts (invertebrate taxonomy and systematics, form and function, evolution, etc.) to be emphasized while exploring the importance of biogenic buildups—and communities that inhabited ecosystems adjacent to those “engines of evolution”—from the past to the present. Students who satisfactorily complete the course achieve seven main learning objectives: They 1) are intimately familiar with the fossil record of marine invertebrate life; 2) understand the evolutionary history of reefs and the ecological roles played by key reef-building invertebrates through time; 3) are able to engage in discussions about paleontological data published in the primary literature; 4) are knowledgeable about the value of paleontological evidence for shedding insights into the decline of ancient and living reefs; 5) gain experience working collaboratively and thinking outside-of-the-box to explore solutions to societal problems linked with the degradation of modern coral reefs; 6) improve scientific writing; and 7) develop a personal style for communicating scientific information to the general public. During classroom discussions, laboratories, a field trip, and museum visit, students explore the anatomy, ecology, evolutionary history, and life-sustaining ecosystem services of shelly animals and associated marine organisms that coexisted in reefs and adjacent habitats past and present. Evolutionary events, including the Cambrian “explosion,” mass extinctions, and gaps in reef existence, are linked to dramatic physical (tectonic) and climatic changes that occurred in Earth's past. Emphasizing evidence for the impact of global change on ancient reef communities alerts students to the value of paleontological data for predicting how modern reefs—and invertebrates living in interconnected marine ecosystems—will respond as the Sixth Extinction gains traction. That topic is the focus of an optional extended study (nine-day field trip offered in alternate years during spring break) of modern and Pleistocene reefs on San Salvador Island, Bahamas.

Community Replacement Pathways: What Do Fossil Sequences Reveal About Marine Ecosystem Transitions?

1990 ◽  
Vol 5 ◽  
pp. 262-272
Author(s):  
William Miller
Keyword(s):  
Fossil Record ◽  
Large Scale ◽  
Marine Ecosystem ◽  
Small Scale ◽  
Data Sets ◽  
Mass Extinctions ◽  
Ultimate Cause ◽  
Long Time ◽  
History Of ◽  
Time And Energy

Paleontologists have lavished much time and energy on description and explanation of large-scale patterns in the fossil record (e.g., mass extinctions, histories of monophyletic taxa, deployment of major biogeographic units), while paying comparatively little attention to biologic patterns preserved only in local stratigraphic sequences. Interpretation of the large-scale patterns will always be seen as the chief justification for the science of paleontology, but solving problems framed by long time spans and large areas is rife with tenuous inference and patterns are prone to varied interpretation by different investigators using virtually the same data sets (as in the controversy over ultimate cause of the terminal Cretaceous extinctions). In other words, the large-scale patterns in the history of life are the true philosophical property of paleontology, but there will always be serious problems in attempting to resolve processes that transpired over millions to hundreds-of-millions of years and encompassed vast areas of seafloor or landscape. By contrast, less spectacular and more commonplace changes in local habitats (often related to larger-scale events and cycles) and attendant biologic responses are closer to our direct experience of the living world and should be easier to interpret unequivocally. These small-scale responses are reflected in the fossil record at the scale of local outcrops.

scholarly journals Case AD, AR, and AS binary evolution and their possible connections with W UMa binaries

2019 ◽  
Vol 492 (2) ◽  
pp. 2731-2738 ◽  
Author(s):  
Dengkai Jiang
Keyword(s):  
Parameter Spaces ◽  
Short Period ◽  
Contact Binaries ◽  
Low Mass ◽  
Orbital Periods ◽  
The Difference ◽  
Binary Evolution ◽  
Detached Binaries ◽  
Period Limit ◽  
The Moment

ABSTRACT Close detached binaries were theoretically predicted to evolve into contact by three subtypes of case A binary evolution, cases AD, AR, and AS, which correspond to the formation of contact during dynamic-, thermal-, and nuclear-time-scale mass transfer phases, respectively. It is unclear, however, what is the difference between contact binaries in these subtypes, and whether all of these subtypes can account for the formation of observed W Ursae Majoris (W UMa) binaries. Using Eggleton’s stellar evolution code with the non-conservative assumption, I obtained the low-mass contact binaries produced by cases AD, AR, and AS at the moment of contact and their parameter spaces. The results support that the progenitors of low-mass contact binaries are detached binaries with orbital periods shorter than $\sim 2\!-\!5\,$ d, and their borderlines depend strongly on the primary mass. In addition, the period–colour relations for cases AR and AS can be in better agreement with that for observed W UMa candidates, but case AD shows a significantly worse agreement. Moreover, cases AR and AS can produce a short-period limit (corresponding to a low-mass limit) at almost any age, e.g. from young age ($\sim 0.2\,$ Gyr) to old age ($\sim 13\,$ Gyr), agreeing with observed W UMa binaries in star clusters, but no such limit occurs for case AD at any age. These results support that cases AR and AS, as opposed to case AD, can lead to W UMa binaries (including young W UMa binaries).

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