If reality is a consciousness hologram and time an illusion, then it stands to reason that there never were Extinction Level Events, just different programmed inserts through which souls virtually experience at different levels of awareness.

Fabric of the Cosmos November 2012 - NOVA Special

In Mythology we find many Flood Stories about the end of an age by means of floods and other catastrophic events, then the start of a new chapter in Earth's history.

In Ancient Alien Theory, humans are a biogenetic experiment created then destroyed over and over again, each time seeking a more advanced human species. This goes along with Hitler's Nazi program, and the Gray Alien Agenda.

In biology and ecology, extinction is the ceasing of existence of a species or group of taxa. The moment of extinction is generally considered to be the death of the last individual of that species. Extinction is usually a natural phenomenon; it is estimated that more than 99.9% of all species that have ever lived are now extinct.

Through evolution, new species are created by speciation - where new organisms arise and thrive when they are able to find and exploit an ecological niche - and species become extinct when are no longer able to survive in changing conditions or against superior competition. A typical species becomes extinct within 10 million years of its first appearance, although some species survive virtually unchanged for hundreds of millions of years.

Descendants may or may not exist for extinct species. Daughter species that evolve from a parent species carry on most of the parent species' genetic information, and even though the parent species may become extinct, the daughter species lives on. In other cases, species have produced no new variants, or none that are able to survive the parent species' extinction. Extinction of a parent species where daughter species or subspecies are still alive is also called pseudoextinction.

However, pseudoextinction is difficult to demonstrate unless one has a strong chain of evidence linking a living species to members of a pre-existing species. For example, it is sometimes claimed that the extinct Hyracotherium, which was an ancient animal similar to the horse, is pseudoextinct, rather than extinct, because there are several extant species of horse, including zebra and donkeys.

However, as fossil species typically leave no genetic material behind, it's not possible to say whether Hyracotherium actually evolved into more modern horse species or simply evolved from a common ancestor with modern horses. Pseudoextinction is much easier to demonstrate for larger taxonomic groups. For example, it could be said that dinosaurs are pseudoextinct, because some of their descendants, the birds, survive today.

Currently, environmental groups and some governments are concerned with the extinction of species due to human intervention, and are attempting to combat further extinctions. Humans can cause extinction of a species through overharvesting, pollution, destruction of habitat, introduction of new predators and food competitors, and other influences.

According to the World Conservation Union (WCU, also known as IUCN), 784 extinctions have been recorded since the year 1500, the arbitrary date selected to define "modern" extinctions, with many more likely to have gone unnoticed. Most of these modern extinctions can be attributed directly or indirectly to human effects.

Endangered species are species that are in danger of becoming extinct; several organizations attempt to preserve recognized endangered species through a variety of conservation programs. Species which are not extinct are termed extant.

Definition

A species becomes extinct when the last existing member of that species dies. Extinction therefore becomes a certainty when no surviving specimens are able to reproduce and create a new generation.

A species may become functionally extinct when only a handful of individuals survive, which are unable to reproduce due to health, age, lack of both sexes (in species that reproduce sexually), or other reasons.

In addition to actual extinction, human attempts to preserve critically endangered species have caused the creation of the conservation status extinct in the wild. Species listed under this status by the WCU are not known to have any living specimens in the wild, and are maintained only in zoos or other artificial environments. Some of these species are functionally extinct.

When possible, modern zoological institutions attempt to maintain a viable population for species preservation and possible future reintroduction to the wild through use of carefully planned breeding programs.

Pinpointing the extinction or pseudoextinction of a species requires a clear definition of that species. The species in question must be identified uniquely from any daughter species, as well as its ancestor species or other closely related populations, if it is to be declared extinct.

Extinction (or replacement) of species by a daughter species plays a key role in the punctuated equilibrium hypothesis of Stephen Jay Gould and Niles Eldredge.

In ecology, extinction is often used informally to refer to local extinction, in which a species ceases to exist in the chosen area of study, but still exists elsewhere.

Permanence

Until recently, it had been universally accepted that the extinction of a species meant the end of its time on Earth. However, recent technological advances have encouraged the hypothesis that through the process of cloning, extinct species may be "brought back to life." Proposed targets for cloning include the mammoth and thylacine. In order for such a program to succeed, a sufficient number of individuals would need to be cloned (in the case of sexually reproducing organisms) to create a viable population size. The cloning of an extinct species has not yet been attempted, due to technological limitations, as well as ethical and philosophical questions.

Causes

There are a variety of causes that can contribute directly or indirectly to the extinction of a species or group of species. Most simply, any species that is unable to survive or reproduce in its environment, and unable to move to a new environment where it can do so, dies out and becomes extinct. Extinction of a species may come suddenly when an otherwise healthy species is wiped out completely, as when toxic pollution renders its entire habitat unlivable; or may occur gradually over thousands or millions of years, such as when a species gradually loses out competition for food to newer, better adapted competitors. Around three species of birds die out every year due to competition.

Genetic and demographic phenomena affect the evolution, and therefore extinction, of species. Regarding the possibility of extinction, small populations which represent an entire species are much more vulnerable to these types of effects.

Natural selection acts to propagate beneficial genetic traits and eliminate weaknesses. However, it is sometimes possible for a deleterious mutation to be spread throughout a population through the effect of genetic drift.

A diverse or "deep" gene pool gives a population a higher chance of surviving an adverse change in conditions. Effects that cause or reward a loss in genetic diversity can increase the chances of extinction of a species. Population bottlenecks can dramatically reduce genetic diversity by severely limiting the number of reproducing individuals and make inbreeding more frequent. The founder effect can cause rapid, individual-based speciation and is the most dramatic example of a population bottleneck.

The degradation of a species' habitat may alter the fitness landscape to such an extent that the species is no longer able to survive and becomes extinct. This may occur by direct effects, such as the environment becoming toxic, or indirectly, by limiting a species' ability to compete effectively for diminished resources or against new competitor species.

Habitat degradation through toxicity can kill off a species very rapidly, by killing all living members through contamination or sterilizing them. It can also occur over longer periods at lower toxicity levels by affecting life span, reproductive capacity, or competitiveness.Habitat degradation can also take the form of a physical destruction of niche habitats.

The widespread destruction of tropical rainforests and replacement with open pastureland is widely cited as an example of this; elimination of the dense forest eliminated the infrastructure needed by many species to survive. For example, a fern that depends on dense shade for protection from direct sunlight can no longer survive with no forest to house it.

Diminished resources or introduction of new competitor species also often accompany habitat degradation. Global warming has allowed some species to expand their range, bringing unwelcome competition to other species that previously occupied that area.

Sometimes these new competitors are predators and directly affect prey species, while at other times they may merely outcompete vulnerable species for limited resources.Vital resources including water and food can also be limited during habitat degradation, causing some species to become extinct.

Humans have been transporting animals and plants from one part of the world to another for thousands of years, sometimes deliberately (e.g., livestock released by sailors onto islands as a source of food) and sometimes accidentally (e.g., rats escaping from boats). In most cases, such introductions are unsuccessful, but when they do become established as an invasive alien species, the consequences can be catastrophic. Invasive alien species can affect native species directly by eating them, competing with them, and introducing pathogens or parasites that sicken or kill them or, indirectly, by destroying or degrading their habitat.

Coextinction

Coextinction of a species is the loss of one species upon the extinction of another. The term was originally used in the context of the extinction of parasitic insects following the loss of their hosts.The term is now used describe the subsequent loss of any interacting species, including predators with their prey, and specialist herbivores with their food source.

The most often cited examples are that of the extinct passenger pigeon and its parasitic louse Columbicola extinctus and Campanulotes defectus. Recently, C. extinctus was rediscovered on band-tailed pigeon and C. defectus was found to be a likely case of misidentification, is the existing Campanulotes flavus. However, even though the passenger pigeon lice story has a happy ending (i.e. rediscovery), it is uncertain that other co-extinctions of other parasites, even on passenger pigeon, have not occurred.

Mass Extinction

There have been at least five mass extinctions in the history of life, and four in the last 3.5 billion years in which many species have disappeared in a relatively short period of geological time. These are covered in more detail in the article on extinction events.

The most recent of these, the K-T extinction 65 million years ago at the end of the Cretaceous period, is best known for having wiped out the non-avian dinosaurs, among many other species.

According to a 1998 survey of 400 biologists conducted by New York's American Museum of Natural History, nearly 70 percent of biologists believe that we are currently in the early stages of a human-caused mass extinction, known as the Holocene extinction event. In that survey, the same proportion of respondents agreed with the prediction that up to 20 percent of all living species could become extinct within 30 years (by 2028). Biologist E.O. Wilson estimated in 2002 that if current rates of human destruction of the biosphere continue, one-half of all species of life on earth will be extinct in 100 years.

Human Extinction

Human extinction refers to the possibility that the human species may become extinct. Although humans are relatively intelligent and adaptive, they could cause an extinction through their own actions, or allow a natural extinction event to occur through negligence. Humans can also possibly die out because of an event that they are incapable of preventing, such as another meteor strike.

Human extinction would be the extinction of the human species, Homo sapiens, whether on Earth (often as the result of a doomsday event) or from the entire universe, provided the species colonizes on other planets.

Attitudes to human extinction vary widely depending on beliefs concerning spiritual survival (souls, heaven, reincarnation, and so forth), the value of the human race, whether the human race evolves individually or collectively, and many other factors. Many religions prophesy an end time to the universe, so eventual human extinction is necessarily a part of the faith of many humans, to the extent that the end time means the absolute end of humanity (see eschatology), except for possibly their "souls".

Many people consider that the extinction of the entire species would be a much worse fate than the death of an individual. Although the mortality of the individual can be accepted as an inevitable part of the human condition, humans can nevertheless expect to attain some measurement of immortality through their progeny, or through contributions or advancement in culture or science. However, the extent to which this "immortality" can be achieved is subject to the continuation of the species as a whole, and human extinction would represent the termination of such expectations.

Fear of human extinction is said to be one of the motivating factors of the environmentalist movements of the 20th and 21st century.

The Permian-Triassic (P-T or PT) extinction event, sometimes informally called the Great Dying, was an extinction event that occurred approximately 251.0 million years ago (mya), forming the boundary between the Permian and Triassic geologic periods. It was the Earth's most severe extinction event, with about 90 percent of all marine species and 70 percent of terrestrial vertebrate species going extinct.

At one time, this die-off was assumed to have been a gradual reduction over several million years. Now, however, it is commonly accepted that the event lasted less than a million years, from 252.3 to 251.4 MYA (both numbers -300,000 years), a very brief period of time in geological terms. Organisms throughout the world, regardless of habitat, suffered similar rates of extinction, suggesting that the cause of the event was a global, not local, occurrence, and that it was a sudden event, not a gradual change.

New evidence from strata in Greenland shows evidence of a double extinction, with a separate, less dramatic extinction occurring 9 million years before the Permian-Triassic (P-T) boundary, at the end of the Guadalupian epoch. Confusion of these two events is likely to have influenced the early view that the extinction was extended.

For some time after the event, fungal species were the dominant form of terrestrial life. Though they only made up approximately 10% of remains found before and just after the extinction horizon, fungal species subsequently grew rapidly to make up nearly 100% of the available fossil record. However, some researchers argue that fungal species did not dominate terrestrial life, as their remains have only been found in shallow marine deposits. Alternatively, others argue that fungal hypha are simply better suited for preservation and survival in the environment, creating an inaccurate representation of certain species in the fossil record.

Explanatory theories

Many theories have been presented for the cause of the extinction, including plate tectonics, an impact event, a supernova, extreme volcanism, the release of frozen methane hydrate from the ocean beds to cause a greenhouse effect, or some combination of factors.

Plate tectonics

At the time of the Permian extinction, all the continents had recently joined to form the super-continent Pangaea and the super-ocean Panthalassa. This configuration radically decreased the extent and range of shallow aquatic environments and exposed formerly isolated organisms of the rich continental shelves to competition from invaders. As the planet's epicontinental systems coalesced; many marine ecosystems, especially ones that evolved in isolation, would not have survived those changes. Pangaea's formation would have altered both oceanic circulation and atmospheric weather patterns, creating seasonal monsoons. Pangaea seems to have formed millions of years before the great extinction, however, and very gradual changes like continental drift alone probably could not cause the sudden, simultaneous destruction of both terrestrial and oceanic life.

Impact event

When large bolides (asteroids or comets) impact Earth, the aftermath weakens or kills much of the life that thrived previously. Release of debris and carbon dioxide into the atmosphere reduces the productivity of life and causes both global warming and ozone depletion. Evidence of increased levels of atmospheric carbon dioxide exist in the fossil record. Material from the Earth's mantle released during volcanic eruption has also been shown to contain iridium, an element associated with meteorites. At present, there is only limited and disputed evidence of iridium and shocked quartz occurring with the Permian event, though such evidence has been very abundantly associated with an impact origin for the Cretaceous-Tertiary extinction event.

If an extraterrestrial impact triggered the Permian extinction event, scientists ask, where is the impact crater? Part of the answer may lie in the fact that there is no Permian-age oceanic crust remaining; all of it has been subducted, so plate tectonics during the last 252 million years have erased any possible P-T seafloor crater.

Adrian Jones, University College London, models the effects of impacts on the Earth's geological crust. After an impact, the crust rebounds to form a large shallow crater. Jones suggests that in a truly massive impact, the combined heat of the impact and rebound is enough to melt the crust. Lava floods through and the crater disappears beneath new crust. If Jones is right, the Permian meteorite crater can't be found because it doesn't exist.

But geologist John Gorter of Agip found evidence of a circular structure 200 kilometers in diameter called the Bedout, in currently submerged continental crust off the northwestern coast of Australia, and geologist Luann Becker, of the University of California, confirmed it, finding shocked quartz and brecciated mudstones.

The geology of the area of continental shelf dates to the end of the Permian. The Bedout impact crater is also associated in time with extreme volcanism and the break-up of Pangaea. "We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time," Dr. Becker explains. "This is what happened 65 million years ago at Chicxulub but was largely dismissed by scientists as merely a coincidence. With the discovery of Bedout, I don't think we can call such catastrophes occurring together a coincidence anymore," Dr. Becker added in a news release.

It has also been proposed that such a collision might heat up ocean waters enough to produce "hypercanes," gigantic storms with winds possibly exceeding the speed of sound. Although not impossible, this theory has little supporting evidence.

Supernova

A supernova occurring within ten parsecs (1 parsec = 3.26 light years) of Earth would produce enough gamma radiation to destroy the ozone layer for several years. The resulting direct ultra-violet radiation from the sun would weaken or kill nearly all existing species. Only those deep in the oceans would be unaffected. Statistical frequency of supernovae suggests that one at the P-T boundary would not be unlikely. A gamma ray burst (the most energetic explosions in the universe; believed to be caused by a very massive supernova (hypernova) or two objects as dense as neutron stars colliding) that occurred within ~6000 light years would produce the same effect.

Volcanism

The P-T boundary was marked with many volcanic eruptions. In the Siberian Traps, now a sub-Arctic wilderness, over 200,000 square kilometers were covered in torrents of lava. The Siberian flood basalt eruption, the biggest volcanic effect on Earth, lasted for millions of years.

The acid rain, brief initial global cooling with each of the bursts of volcanism, followed by longer-term global warming from released volcanic gases, and other weather effects associated with enormous eruptions could have globally threatened life.

The theory is debated if volcanic activity, over such a long time, could alter the climate enough to kill off 95% of life on Earth. Volcanic activity affects the concentration of atmospheric gases directly, and, indirectly, the oceanic dissolved gases.

Increases in carbon dioxide enhance the greenhouse effect and cause global warming, which would reduce the temperature gradient between the equator and the poles. As a result, thermohaline circulation would slow and eventually stop.

The oceans would stagnate, and nutrients would fail to disperse themselves. Many marine ecosystems rely on upwelling and circulation of nutrients, oxygen included; without the regular circulation, organisms would starve or suffocate.

In addition, sulfur and particulates contribute to cooling, or volcanic winter, which usually lasts three to six months. Combinations of the two effects could produce a cooling cycle in which the climate alternatively warms then cools. Such temperature fluctuations could cause convective overturn of the oceans, bringing anoxic bottom waters to the surface; in an already oxygen-deprived environment, this would be fatal to many forms of life. Significant evidence supports this theory.

Fluctuations in air and water temperature are evident in the fossil record, and the uranium/thorium ratios of late Permian sediments indicate that the oceans were severely anoxic around the time of the extinction. Numerous indicators of volcanic activity at the P-T boundary are present, though they are similar to bolide impact indicators, including iridium deposits.

The volcanism theory has the advantage over the bolide theory, though, in that it is certain that an eruption of the Siberian Traps - the largest known eruption in the history of Earth - occurred at this time, while no direct evidence of bolide impact has been located.

Extinction Wikipedia

ELE - Extinction Level Event Wikipedia

Researchers say habitat loss and tropical cooling were to blame for mass extinction   PhysOrg - April 10, 2012
The second-largest mass extinction in Earth's history coincided with a short but intense ice age during which enormous glaciers grew and sea levels dropped. Although it has long been agreed that the so-called Late Ordovician mass extinction which occurred about 450 million years ago was related to climate change, exactly how the climate change produced the extinction has not been known. Now, a team led by scientists at the California Institute of Technology (Caltech) has created a framework for weighing the factors that might have led to mass extinction and has used that framework to determine that the majority of extinctions were caused by habitat loss due to falling sea levels and cooling of the tropical oceans.

New technique unlocks secrets of ancient ocean   PhysOrg - October 11, 2011
Earth's largest mass extinction event, the end-Permian mass extinction, occurred some 252 million years ago. An estimated 90 percent of Earth's marine life was eradicated. To better understand the cause of this "mother of all mass extinctions," researchers from Arizona State University and the University of Cincinnati used a new geochemical technique. The team measured uranium isotopes in ancient carbonate rocks and found that a large, rapid shift in the chemistry of the world's ancient oceans occurred around the extinction event.

Has the Earth's sixth mass extinction already arrived?   PhysOrg - March 2, 2011
With the steep decline in populations of many animal species, from frogs and fish to tigers, some scientists have warned that Earth is on the brink of a mass extinction like those that occurred only five times before during the past 540 million years. Each of these 'Big Five' saw three-quarters or more of all animal species go extinct.

Humans on Verge of Causing 6th Great Mass Extinction   Live Science - March 2, 2011
Mass extinctions include events in which 75 percent of the species on Earth disappear within a geologically short time period, usually on the order of a few hundred thousand to a couple million years. It's happened only five times before in the past 540 million years of multicellular life on Earth. (The last great extinction occurred 65 million years ago, when the dinosaurs were wiped out.) At current rates of extinction, the study found, Earth will enter its sixth mass extinction within the next 300 to 2,000 years.

Mystery of Ancient Extinction in Earth's Oceans Revealed   Live Science - January 4, 2011
About 375 million years ago, the diversity of species in the Earth's oceans plummeted - not because more species were going extinct, but because fewer new groups of organisms were forming. A new study identifies a culprit: invasive species. The crisis of the Late Devonian Period is typically considered to be one of the "Big Five" mass extinctions; however, this terminology is inaccurate, according to Alycia Stigall, the study researcher and an associate professor of geology at Ohio University.

Long recovery from the largest extinction in history revealed in China's new fossil site   PhysOrg - December 22, 2010
A major new fossil site in south-west China has filled in a sizeable gap in our understanding of how life on this planet recovered from the greatest mass extinction of all time. Some 250 million years ago, at the end of the time known as the Permian, life was all but wiped out during a sustained period of massive volcanic eruption and devastating global warming. Only one in ten species survived, and these formed the basis for the recovery of life in the subsequent time period, called the Triassic. The new fossil site - at Luoping in Yunnan Province - provides a new window on that recovery, and indicates that it took about 10 million years for a fully-functioning ecosystem to develop.

Cache in Chinese Mountain Reveals 20,000 Prehistoric Fossils   Live Science - December 22, 2010
A giant cache of nearly 20,000 fossil reptiles, shellfish and a host of other prehistoric creatures unearthed from a mountain in China is now revealing how life recovered after the most devastating mass extinction on Earth. This research could help point out which species might be more or less susceptible to extinction nowadays, and how the world might recover from the damage caused by humanity, scientists added. Life was nearly completely wiped out approximately 250 million years ago by massive volcanic eruptions and devastating global warming. Only one in 10 species survived this cataclysmic end-Permian event.

Algeo tracks evidence of 'The Great Dying'   PhysOrg - October 28, 2010
More than 251 million years ago, at the end of the Permian period, Earth almost became a lifeless planet. Around 90 percent of all living species disappeared then, in what scientists have called "The Great Dying."

Prehistoric Fish Extinction Paved the Way for Modern Vertebrates; Event of Unknown Origin Occurred as First Vertebrates Tested Land   Science Daily - May 20, 2010
A mass extinction of fish 360 million years ago hit the reset button on Earth's life, setting the stage for modern vertebrate biodiversity, a new study reports.

Antarctica Served as Climatic Refuge in Earth's Greatest Extinction Event   Science Daily - December 4, 2009

The largest known mass extinction in Earth's history, about 252 million years ago at the end of the Permian Period, may have been caused by global warming. A new fossil species suggests that some land animals may have survived the end-Permian extinction by living in cooler climates in Antarctica. Jorg Frobisch and Kenneth D. Angielczyk of The Field Museum together with Christian A. Sidor from the University of Washington have identified a distant relative of mammals, Kombuisia antarctica, that apparently survived the mass extinction by living in Antarctica.

Mass Extinction: Why Did Half of N. America's Large Mammals Disappear 40,000 to 10,000 Years Ago?   Science Daily - November 27, 2009

Years of scientific debate over the extinction of ancient species in North America have yielded many theories. However, new findings from J. Tyler Faith, GW Ph.D. candidate in the hominid paleobiology doctoral program, and Todd Surovell, associate professor of anthropology at the University of Wyoming, reveal that a mass extinction occurred in a geological instant.

"Nanodiamond" Find Supports Comet Extinction Theory 12,900 years ago   National Geographic - January 6, 2009
The discovery of tiny "nanodiamonds" supports a controversial theory that a catastrophic bombardment of space rocks altered the course of Earth history. About 12,900 years ago, Earth was escaping the grips of an ice age when something triggered a sudden refreeze. The resulting 1,300-year cold spell coincides with the extinction of a host of massive mammals such as woolly mammoths, dire wolves, and sabertooths.

Six North American Sites Hold 12,900-year-old Nanodiamond-rich Soil   Science Daily - January 3, 2009
Soil rich in diamond dust discovered across North America reinforces a theory that falling meteors caused the extinction of mammoths and other animals.

Sea die-out blamed on volcanoes BBC - July 16, 2008
Undersea volcanic activity has been blamed for a mass extinction in the seas 93 million years ago. In the so-called "anoxic event" of the late Cretaceous Period, the ocean depths became starved of oxygen, wiping out swathes of marine organisms. Researchers from the University of Alberta, Canada, found a tell-tale signature of underwater volcanism in rocks dating to the period. Their findings have been published in the journal Nature. At the time of the anoxic event, the average temperatures were higher than those of today, researchers say.

Greatest Mysteries: What Causes Mass Extinctions? Live Science - August 8, 2007

They are known ominously as the Big Five - the five greatest mass extinctions over the past 500 million years, each of which is thought to have annihilated anywhere from 50 to 95 percent of all species on the planet. Many unsolved mysteries remain regarding these disasters, perhaps the greatest of which is what caused each of them. But research is uncovering how these extinction events dictated the fate of life on this planet - for instance, determining which animals first crawled onto land and which ruled the oceans.

Ancient Mass Extinctions Caused by Cosmic Radiation, Scientists Say National Geographic - April 20, 2007
Cosmic rays produced at the edge of our galaxy have devastated life on Earth every 62 million years, researchers say. The finding suggests that biodiversity has been strongly influenced by the motion of the solar system through the Milky Way and of the galaxy's movement through intergalactic space.

Fossil research suggests 'mass dying' triggered teeming oceans Guardian - November 23, 2006
A cataclysmic mass extinction that devastated life on Earth millions of years ago is the unlikely reason such a rich variety of life is found in the oceans today, scientists have discovered. Around 250m years ago at the end of the Permian era the Earth experienced its most dramatic loss of life, when an estimated 95% of marine species and 70% of land animals were wiped out. Scientists are uncertain what caused the extinction, but many suspect rapid environmental upheaval caused by vast volcanic eruptions were at least in part to blame.

Dramatic shift from simple to complex marine ecosystems occurred 250M years ago at mass extinction PhysOrg - November 23, 2006
The earth experienced its biggest mass extinction about 250 million years ago, an event that wiped out an estimated 95% of marine species and 70% of land species. New research shows that this mass extinction did more than eliminate species: it fundamentally changed the basic ecology of the world's oceans.

"Dinosaur Killer" Asteroid Only One Part of New Quadruple-Whammy Theory National Geographic - October 30, 2006
Offshore of Mexico's Yucatan Peninsula is a 110-mile-wide (180-kilometer-wide) crater dubbed Chicxulub, widely believed to be the site of an asteroid impact 65 million years ago that wiped out the dinosaurs. The mass extinction, thought to have obliterated two-thirds of the world's species in total, has been dubbed the K-T extinction because it bridges the Cretaceous and Tertiary geologic periods. But a single asteroid impact doesn't tell the whole story, says a small but vocal group of geologists led by Princeton University paleontologist Gerta Keller in New Jersey.

Great extinction came in phases BBC - April 1, 2005
The greatest mass extinction recorded in Earth history did not occur as a result of one single cataclysmic event. A joint UK-Chinese team tell Nature magazine the disaster that befell the planet 250 million years ago must have happened in phases. Their conclusion is based on the abundance of "organic fossils" found in rocks at Meishan in southern China. These suggest there were at least two episodes to the mass die-off that saw up to 95% of lifeforms disappear.

The Great Dying MSNBC - May 13, 2004

Millions of years before the dinosaurs vanished, an even bigger mass extinction wiped out more than 90 percent of the species on Earth. Now scientists think they may have evidence of an impact crater that contributed to the 'Great Dying.' The Permian-Triassic extinction took place 250 million years ago in a vastly different world from today's. Scientists have debated its cause for years. The end of the dinosaurs 65 million years ago is widely thought to have been caused by a meteor impact off Mexico's Yucatan Peninsula.

Climate Change Plus Human Pressure Caused Large Mammal Extinctions In Late Pleistocene Science Daily - October 4, 2004
A University of California, Berkeley, paleobiologist and his colleagues warn that the future of the Earth's mammals could be as dire as it was between 50,000 and 10,000 years ago, when a combination of climate change and human pressure resulted in the extinction of two-thirds of all large mammals on the planet.

The Great Dying NASA - January 28, 2002
Somehow, most of the life on Earth perished in a brief moment of geologic time roughly 250 million years ago. Scientists call it the Permian-Triassic extinction or "the Great Dying" -- not to be confused with the better-known Cretaceous-Tertiary extinction that signaled the end of the dinosaurs 65 million years ago. Whatever happened during the Permian-Triassic period was much worse: No class of life was spared from the devastation. Trees, plants, lizards, proto-mammals, insects, fish, mollusks, and microbes -- all were nearly wiped out. Roughly 9 in 10 marine species and 7 in 10 land species vanished. Life on our planet almost came to an end.