Biological Sciences
Mass Extinction
Mass extinction refers to a widespread and rapid decrease in the biodiversity on Earth. It is characterized by the loss of a large number of species within a relatively short period of time, leading to significant changes in ecosystems. Mass extinctions have occurred several times in the history of the planet, with the most well-known being the event that led to the extinction of the dinosaurs.
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11 Key excerpts on "Mass Extinction"
eBook - ePubWhen Life Nearly Died
The Greatest Mass Extinction of All Time
- Michael J. Benton(Author)
- 2015(Publication Date)
- Thames and Hudson Ltd(Publisher)
Background extinction, extinction events, and Mass Extinctions. There have clearly been times when extinction rates have gone up, times that stand out as extinction events of some kind. Extinction events are usually restricted in some way, perhaps the loss of all the large, cold-adapted mammals at the end of the Pleistocene, or the loss of life on some Pacific islands as a result of a huge volcanic eruption or other catastrophe. A Mass Extinction is the largest kind of extinction event. It is important to try to define the meanings of these terms, not least because many biologists have claimed that we are living through the sixth, human-induced, Mass Extinction today.The big five Mass Extinctions share many features in common, but differ in others. Three things happened in all the Mass Extinctions of the past: •many species became extinct, generally more than 40 to 50% •the extinct forms span a broad range of ecologies, and they typically include marine and non-marine forms, plants and animals, microscopic and large forms •the extinctions all happened within a short time, and hence relate to a single cause, or cluster of interlinked causes.These points all seem clear, but palaeontologists have struggled to be more precise. Just how many species should disappear, and how fast, for an event to stand apart from background extinctions as a Mass Extinction? Attempts have been made to find a more quantitative definition of which extinctions are truly Mass Extinctions, and which are more localized or ecologically restricted events, but none of these efforts has really been satisfactory.A statistical test?
In 1982, the palaeontologists David Raup and Jack Sepkoski of the University of Chicago8 claimed that they had found such a test for Mass Extinctions, and their idea was simple. They argued that if times of Mass Extinctions were associated with exceptionally high rates of extinction, then these should stand out clearly from normal background extinction rates. Raup and Sepkoski calculated a mean rate of disappearance of marine animal families, per million years, for each geological stage (average duration, 5–6 myr.). So, over a time span of the last 600 myr., they assessed about 100 separate extinction rates.Raup and Sepkoski believed that they could apply a simple statistical technique to these measurements: regression analysis. This is a grand term for fitting a line to a set of points on a graph. The ideal is that a straight line can be fitted, and that most of the points will lie close to it. There was absolutely no reason why Raup and Sepkoski could have fitted a line to their measurements of extinction rates through time, but they succeeded. Most of their 100 extinction data points fell very close to a straight line, and that straight line was declining through time (Fig. 18
- Michael J. Benton, David A. T. Harper(Authors)
- 2020(Publication Date)
- Wiley-Blackwell(Publisher)
Biodiversity and extinction are current concerns for conservationists and indeed for all citizens, but these topics are clearly key areas of research for paleobiologists too. Earth has had a long history, and it is important to explore how life expanded from, presumably, a single species at some point deep in the Precambrian, to the many millions of species on Earth today. In fact, new species emerge all the time, and other species go extinct, and the overall increase in species numbers, or diversification, depends on the balance of those two processes, speciation and extinction.The most spectacular extinctions are known as Mass Extinctions, times when a large cross‐section of species died out rather rapidly. There may have been only five or six Mass Extinctions throughout the known history of life, although there were many extinction events, smaller‐scale losses of species, often in a particular region or involving species with a particular shared ecology.The serious study of Mass Extinctions is a relatively new research field, dating from the 1980s onwards, and it has wide interdisciplinary links across stratigraphy, geochemistry, climate modeling, ecology, conservation, and even astronomy. The study of Mass Extinctions involves careful hypothesis testing (see Chapter 1 : Section “What is science? ”) at all levels, from the broadest scale (“Was there a Mass Extinction at this time? Was it caused by a meteorite impact or a volcanic eruption?”) to the narrowest (“How many brachiopod genera died out in my field section? Does their extinction coincide with a negative carbon isotope anomaly? Do the sediments record any evidence for climate change across this interval?”). Mass Extinctions, and smaller extinction events, provide vital information for understanding the history of life, yet they are unique paleontological phenomena that cannot be predicted from the modern‐day standpoint. In practical terms, the study of extinctions and Mass Extinctions draws on such a broad array of disciplines that research involves teamwork, often with groups of 5 or 10 specialists, who pool their expertise and resources to carry out a study.In this chapter, we explore what we mean by diversity, extinctions, and Mass Extinctions. There are practical difficulties in measuring both diversity and rates of speciation and extinction in the past, and it is important to relate the paleobiological evidence to our understanding of modern global biodiversity and extinction threat. We shall then explore the two most heavily studied events, the Permian‐Triassic Mass Extinction of 252 million years ago, and the Cretaceous‐Paleogene Mass Extinction of 66 million years ago, in most detail. Finally, it is important to consider how paleobiology informs the current heated debates about extinctions now and in the future (Box 8.1
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
______________________________ WORLD TECHNOLOGIES ______________________________ Chapter 2 Mass Extinction and Modern Extinction Mass Extinction Extinction Event Vertical axis - percentage extinction of genera, horizontal axis - mya (millions of years ago) An extinction event (also known as: Mass Extinction ; extinction-level event , ELE, or biotic crisis ) is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation. Because the majority of diversity and biomass on earth is microbial, and thus difficult to measure, Mass Extinctions have little effect on the total diversity and abundance of life, but rather affect the easily observed, biologically complex component of the biosphere. Over 98% of documented species are now extinct, but extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic ______________________________ WORLD TECHNOLOGIES ______________________________ families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land organisms. Since life began on Earth, several major Mass Extinctions have significantly exceeded the background extinction rate. The most recent, Cretaceous–Tertiary extinction event, which occurred approximately 65.5 million years ago (Ma), was a large-scale Mass Extinction of animal and plant species in a geologically short period of time. In the past 540 million years there have been five major events when over 50% of animal species died. There probably were Mass Extinctions in the Archean and Proterozoic Eons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record.
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 2 Extinction Event Vertical axis - percentage extinction of genera, horizontal axis - mya (millions of years ago) An extinction event (also known as: Mass Extinction ; extinction-level event , ELE, or biotic crisis ) is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation. Because the majority of diversity and biomass on earth is microbial, and thus difficult to measure, Mass Extinctions have little effect on the total diversity and abundance of life, but rather affect the easily observed, biologically complex component of the biosphere. Over 98% of documented species are now extinct, but extinction occurs at an uneven rate. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine invertebrates and vertebrates every million years. Marine fossils are mostly used to measure extinction rates because of their superior fossil record and stratigraphic range compared to land organisms. ________________________ WORLD TECHNOLOGIES ________________________ Since life began on Earth, several major Mass Extinctions have significantly exceeded the background extinction rate. The most recent, the Cretaceous–Tertiary extinction event, occurred 65 million years ago, and has attracted more attention than all others as it marks the extinction of nearly all dinosaur species, which were the dominant animal class of the period. In the past 540 million years there have been five major events when over 50% of animal species died. There probably were Mass Extinctions in the Archean and Proterozoic Eons, but before the Phanerozoic there were no animals with hard body parts to leave a significant fossil record. Estimates of the number of major Mass Extinctions in the last 540 million years range from as few as five to more than twenty.
eBook - PDFArk of the Broken Covenant
Protecting the World's Biodiversity Hotspots
- John Charles Kunich(Author)
- 2003(Publication Date)
- Praeger(Publisher)
EXTINCTIONS THROUGH THE AGES I do not intend to set forth an exhaustive, all-encompassing account of the massive scientific literature on the history of extinction, nor the nature and extent of the contemporary extinction event. Many entire books and scholarly journal articles have been devoted to these complex and difficult topics, and there are important areas within this field in which much scien- tific research remains to be done. I intend rather to offer a concise summary of some of the salient points on which modern science has come to some common understanding, and in so doing, to lay the foundation for the re- mainder of this book. Extinction is, of course, a normal event in the life cycle of a species, much as death is a part of life for any individual organism. Some species persist much longer than others, just as the members of any group enjoy divergent life spans. This natural ebb and flow of life has always been an intrinsic ele- ment of the living planet. It is when extinctions occur at a rate significantly higher than the normal or background level that something extraordinary is evidently at work. These events are known as “Mass Extinctions” (or “extinction spasms”), which have been defined, with deliberate vagueness, as the extinction of a significant proportion of the world’s biota in a geologically insignificant period of time. 1 It is generally accepted that there have been no fewer than five mass ex- tinctions in the earth’s history, at least during the Phanerozoic Eon (the vast expanse of time which includes the present day). These “big five” mass ex- tinctions occurred at the boundaries between the following geological peri- ods: Ordovician-Silurian (O-S); near the end of the Upper Devonian (D) (usually known as the Frasnian-Famennian events, or F-F); Permian-Triassic (P-Tr); Triassic-Jurassic (Tr-J); and Cretaceous-Tertiary (K-T).
- Michael J. Benton, David A. T. Harper(Authors)
- 2020(Publication Date)
- Wiley-Blackwell(Publisher)
Mass Extinctions, and smaller extinction events, provide vital infor- mation for understanding the history of life, yet they are unique paleontological phenom- ena that cannot be predicted from the mod- ern‐day standpoint. In practical terms, the study of extinctions and Mass Extinctions draws on such a broad array of disciplines that research involves teamwork, often with groups of 5 or 10 specialists, who pool their expertise and resources to carry out a study. In this chapter, we explore what we mean by diversity, extinctions, and mass extinc- tions. There are practical difficulties in meas- uring both diversity and rates of speciation and extinction in the past, and it is impor- tant to relate the paleobiological evidence to our understanding of modern global biodi- versity and extinction threat. We shall then explore the two most heavily studied events, the Permian‐Triassic Mass Extinction of 252 million years ago, and the Cretaceous‐ Paleogene Mass Extinction of 66 million years ago, in most detail. Finally, it is impor- tant to consider how paleobiology informs Figure 8.1 An image of the dodo from another era. Lewis Carroll introduced the dodo as a kindly and wise old gentleman in Alice Through the Looking Glass, although at the time most people probably regarded the dodo as rather foolish. Driven to extinction in the seventeenth century by overhunting, the dodo is now an image of human thoughtlessness. BIODIVERSITY, EXTINCTION, AND Mass Extinction 195 the current heated debates about extinctions now and in the future (Box 8.1). THE DIVERSIFICATION OF LIFE Onward and upward An accepted principle of evolution is that all modern and ancient life on Earth is part of a single great phylogenetic tree, and there must have been a time in the Precambrian when there was only one species (see Chapter 9: Section “Introduction”).
Available until 23 Dec |Learn moreGrowth Growth Growth
Human History and the Planetary Catastrophe
- Julian Cobbing(Author)
- 2024(Publication Date)
- Mvusi Books(Publisher)
182 19. The Current Mass Extinction There have been six major extinction events in the 3.8 billion years since the beginning of life on Earth. 259 The first was the decimation of single cell life as a result of the oxygen crisis around 2 billion BP. Since multi- celled life started around 700 million BP, there have been a further five extinctions in which high percentages of the Earth’s life system were wiped out. The first was the Ordovician extinction around 440 million BP, the second the late Devonian extinction around 370 million BP, and the third, the most brutal, the Permian-Triassic extinction around 250 million BP, which destroyed around 90% of the planet’s marine life and 70% of land-dwelling vertebrates. The fourth, the Triassic-Jurassic extinction, of around 200 million BP, killed off high percentages of both marine and land life. All these extinctions were rooted in natural causes – still being debated – such as falling sea levels or volcanic eruptions. The fifth, the Cretaceous-Paleogene event around 60 million BP, which destroyed 30%-40% of life, is thought to have been caused by the planet being hit by an asteroid. This coincided with the extinction of the dinosaurs and enabled the evolutionary rise of small mammals from which we are descended. 260 The extinction we are now experiencing, the sixth, is the first to be caused by the activities of a single species within the life system. Humans are now a ‘geophysical force, the first species in the history of the planet to attain that dubious distinction,’ writes E.O. Wilson. ‘How much extinction is occurring today?’ he asks: ‘Researchers generally agree that it is catastrophically high, somewhere between one thousand and ten thousand times the rate before humans began to exert a significant pressure on the environment.’ And it is happening at unprecedented speed, faster than all the other extinctions. 261 There are various drivers of the current extermination.
eBook - PDFBiodiversity Erosion
Issues and Questions
- Christian Lévêque(Author)
- 2022(Publication Date)
- Wiley-ISTE(Publisher)
I would also point out that the five major Mass Extinctions have been identified in marine species. But on the continents we know – again, according to paleontologists – that climate change has affected the biosphere on many occasions, in all likelihood leading to major upheavals in biological diversity. Do we have the balance sheets to claim today that the human’s action is unprecedented? In these unfounded accusations against humankind, who will bring tangible proof of guilt or acquittal? In reality, the theme of biodiversity decline is the hobbyhorse of activists with a theological vision of nature that gives rise to a battle of “virtual figures”, that is, speculations obtained from debatable theoretical hypotheses, seeking to prove the guilt of the human species at all costs. As we shall see, we find ourselves in a public game of one-upmanship which does not honor science. A bit of restraint and humility in the words of those who claim to speak in the name of science is in order. 6.1. The laborious calculation of the extinction rate One of the topics of debate is the species extinction rate, that is, the number of species that become extinct in a given period per million existing species. The idea is simple in theory: to quantify the decline of biodiversity, we calculate the current rate of species extinction, under the influence of humans, and compare it to a supposedly “natural” rate of extinction that can be described as “background noise” calculated from what we know about fossil species. It remains to put this idea to the test of the data. And this is where the great battle of numbers begins! Controversies Surrounding the Extinction Rate 69 To compare past and present extinctions, Pimm et al. (1995) developed a metric based on the number of extinctions (E) per million species per year (MSY), that is, E/MSY.
eBook - PDF- Anthony J. Martin(Author)
- 2009(Publication Date)
- Wiley-Blackwell(Publisher)
What this extinction means in terms of how much ecosystems will change is unknown, but the world would certainly be a very different one without them (Chapter 15). The bulk of recent scientific evidence has led to the hypothesis that humans are currently observing a sixth Mass Extinction in the Phanerozoic Eon. Moreover, this Mass Extinction has been correlated with human alteration of habitats through: 1 introduced species; 2 resource acquisition; 3 pollution; and 4 global climate change. Documenting to what degree human impact is causing extinctions is actually the only controversial point within the scientific community regarding the modern Mass Extinction. In this case, separating so-called normal extinctions that would have happened without human influence, such as those at the end of the Permian or Cretaceous Periods, from those caused by humans, is problematic. However, so far the only species in the history of the Earth shown to have been ultimately respons- ible for the extinction of another species is Homo sapiens. The recognized human causes of extinctions include the following factors, introduced earlier: n Pollution of ecosystems with chemicals that disrupt reproductive cycles, documented particularly in predatory birds such as eagles, hawks, and other raptors (Fig. 16.10). n Alteration of habitats through deforestation or filling wetland areas for development. n Harvesting, hunting, or purposeful elimination of organisms targeted as pests. n Changing the biogeographic distribution of previously isolated populations, resulting in competition for resources, parasitism, and predation where it did not exist before the introduction of the imported species. 507 16 DINOSAUR EXTINCTIONS Even in cases when humans were not the species that caused the ecological dis- turbance that resulted in local extinctions, humans were still ultimately respons- ible for those extinctions.
eBook - ePubRereading the Fossil Record
The Growth of Paleobiology as an Evolutionary Discipline
- David Sepkoski(Author)
- 2012(Publication Date)
- University of Chicago Press(Publisher)
CHAPTER NINEThe Dynamics of Mass ExtinctionsDuring the 1970s, the study of extinction became a more and more prominent part of paleobiologists’ agenda for rereading the fossil record. However, many of the most active proponents of paleobiology during this time expressed frustration at the lack of a coherent theory that explained the role of Mass Extinctions in macroevolution. For example, it was clear that extinctions influenced the patterns of diversity that paleontologists like Valentine, Raup, and Sepkoski were investigating, and even the MBL simulation project recognized extinction as an important variable in evolution. Norman Newell’s pioneering work in the 1960s established a new legitimacy for analysis of Mass Extinctions, and helped relieve some of the stigma traditionally associated with “catastrophism.” But important questions about extinction—and especially Mass Extinction—persisted: How frequent were major episodes of extinction? What were their causes and mechanisms? How geographically widespread were the largest extinctions? How could major extinctions be reliably recognized—separated from background noise—in large fossil data sets? And, most broadly, what role did extinction have in determining the patterns of life’s history?These questions were central to the project of rereading the fossil record. They also went to the heart of the revision of the traditional synthetic view of evolution that many paleobiologists were trying to establish. Darwin himself downplayed the evolutionary significance of extinction in Origin of Species : extinction, he believed, was essentially just the flip side of natural selection—the elimination of the “unfit”—and therefore required no independent causal explanation or analysis. In particular, Darwin rejected most evidence of Mass Extinctions as examples of the imperfection of paleontological data; episodes where large numbers of taxa appeared to disappear suddenly from the fossil record could be attributed, he thought, to the extreme imperfection of the geological record. There are a variety of good historical reasons for his position. In the first place, Mass Extinctions were, in the 19th century, still closely connected with the taint of catastrophism that many scientists, particularly in Britain, associated with natural theology. Secondly, the known fossil record in Darwin’s day was
eBook - ePubThe Pandora Principle
The destructive power of creation
- Norbert Georg Schwarz(Author)
- 2019(Publication Date)
- Books on Demand(Publisher)
Thus, life on earth achieved a level which allowed Mass Extinction to be detected in the fossil record. It is difficult to observe a massive extinction of bacterial and viral microorganisms, especially when considering events in the distant past, of which multicellular organisms have left only very few traces. I have thus restricted my account to the five great Mass Extinctions of multicellular complex organisms.It is only in the past 200 years that discoveries have been catalogued systematically in palaeontology. Not only interesting fossil discoveries are important, but also linking the insights and classifying new discoveries into taxonomic systems. When tracking the course of species known from the fossil record over a period of time, it becomes apparent that there have been repeated instances of a collapse in the diversity of species: this can be seen when geological layers with a rich variety of fossils of all kinds are covered by layers which seem to be barren and devoid of species – and that worldwide. The Sepkoski curve, a database of species diversity, named after the palaeontologist Jack Sepkoski (d. 1999) shows many high and low points. The five low points are referred to as the big five Mass Extinctions [137 ].The big five Mass Extinctions
As already mentioned, I will restrict my observations to the five great Mass Extinctions of multicellular complex organisms. This serves to provide the basis for an overview of the history of Mass Extinction on earth, albeit only a very patchy one. The emergence and decay of species on earth is part and parcel of what life is about. For the five Mass Extinctions set out in table 6
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