Mass Extinctions (Future Warnings?)
A study of historic and "recent" prehistoric catastrophes shows that there are two types of Worldwide Catastrophes: the Comet Catastrophes and the Volcanic Catastrophes. The first type is the most dangerous and is responsible for the most casualties.
The largest known mass extinctions
The number of 405k years (see Milankovitch eccentricity cycle)
I have collected other information too:
The fossil record of the earliest Cambrian, just after the Ediacaran period, shows a sudden increase in burrowing activity and diversity. However, the Cambrian explosion of animals that gave rise to body fossils did not happen instantaneously. This implies that the "explosion" did not represent animals "replacing" the incumbent organisms, and pushing them gradually to extinction; rather, the data are more consistent with a radiation of animals to fill in vacant niches, left empty as an extinction cleared out the pre-existing fauna.
The concept that all Ediacarans became extinct at the start of the Cambrian is dealt a death knell if any post-Ediacaran survivors are found. Organisms from the lower Cambrian, such as Thaumaptilon, were once thought to be Ediacarans, but this hypothesis no longer has many adherents. One possible Ediacaran survivor whose status is still open to scrutiny is Ediacaria booleyi, a purported holdfast structure known from the upper Cambrian. If this does turn out to be a true Ediacaran, the biota cannot have disappeared completely. Disbelievers have claimed that the fossils don't actually have a biological origin, which doesn't seem to be the case — evidence is mounting to suggest that it is an organism (or at least of biological origin, perhaps a microbial colony), just not one that is related to the Ediacara biota.
This is the Sinsk Event and it occurred at the end of the Early Cambrian Botomian Stage (Zhuravlev and Wood 1996). Currently little is known about this ancient biotic crisis although an association with sea-level rise, black shales and a major sulphur isotope excursion suggests that, like many younger extinction events, it may related to the spread of marine anoxia (Hough et al., 2006). Recent dating of a giant flood basalt province in Australia, the Kalkarindji Province, reveals that this extinction is also the first of many to be associated with flood basalt volcanism (Glass and Phillips 2006; Evins et al., 2009). The Botomian witnessed a mass extinction that may have been even more severe than the end Permian extinction, in terms of absolute percentages of species lost. Some 83% of genera of hard-shelled or -bodied animals did not survive into the Middle Cambrian.
The Cambrian-Ordovician extinction event occurred approximately 488 million years ago. This early Phanerozoic Eon extinction event eliminated many brachiopods and conodonts, and severely reduced the number of trilobite species.
It was preceded by the less-documented (but probably worse) End Botomian event around 517 million years ago and the Dresbachian event about 502 million years ago
The Ordovician-Silurian extinction event, or quite commonly the Ordovician extinction, was the third-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct and second largest overall in the overall loss of life. Between about 450 Ma to 440 Ma, two bursts of extinction, separated by one million years, appear to have happened. This was the second biggest extinction of marine life, ranking only below the Permian extinction. At the time, all known life was confined to the seas and oceans. More than 60% of marine invertebrates died including two-thirds of all brachiopod and bryozoan families. Brachiopods, bivalves, echinoderms, bryozoans and corals were particularly affected. The immediate cause of extinction appears to have been the movement of Gondwana into the south polar region. This led to global cooling, glaciation and consequent sea level fall. The falling sea level disrupted or eliminated habitats along the continental shelves. Evidence for the glaciation was found through deposits in the Sahara Desert. A combination of lowering of sea level and glacially-driven cooling are likely driving agents for the Ordovician mass extinction.
The late Devonian crash in biodiversity was more drastic than the familiar extinction event that closed the Cretaceous: a recent survey (McGhee 1996) estimates that 22 percent of all the families of marine animals (largely invertebrates) were eliminated. The family is a great unit, and to lose so many signifies a deep loss of ecosystem diversity. On a smaller scale, 57% of genera and at least 75% of species did not survive into the Carboniferous. These latter estimates need to be treated with a degree of caution, as the estimates of species loss depend on surveys of Devonian marine taxa that are perhaps not well enough known to assess their true rate of losses, so it is difficult to estimate the effects of differential preservation and sampling biases during the Devonian.
The Permian-Triassic (P-Tr) extinction event, informally known as the Great Dying, was an extinction event that occurred 251.4 million years ago, forming the boundary between the Permian and Triassic geologic periods. It was the Earth's most severe extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It is the only known mass extinction of insects. Some 57% of all families and 83% of all genera were killed. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after other extinction events.
The volcanic eruptions thought responsible for Earth's largest mass extinction — which killed more than 70 percent of plants and animals 250 million years ago — is still taking lives today. That's the conclusion of a new study showing, for the first time, that the high silica content of coal in one region of China may be interacting with volatile substances in the coal to cause unusually high rates of lung cancer.
Scenarios explaining what happened at the greatest mass extinction event of them all at the end of the Permian Period have been complex amalgams of climate change perhaps rooted in plate tectonics movements. Very recently, however, evidence suggests that a bolide impact similar to the end-Cretaceous event may have been the cause.
The Triassic-Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, 199.6 million years ago, and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas a whole class (conodonts) and 20% of all marine families disappeared. On land, all large crurotarsans (non-dinosaurian archosaurs) other than crocodilians, some remaining therapsids, and many of the large amphibians were wiped out. At least half of the species now known to have been living on Earth at that time went extinct. This event vacated terrestrial ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassic period. This event happened in less than 10,000 years and occurred just before Pangaea started to break apart.
The term Toarcian turnover, alternatively the Toarcian extinction, the Pliensbachian-Toarcian extinction, or the Early Jurassic extinction, refers to the wave of extinctions that marked the end of the Pliensbachian stage and the start of the Toarcian stage of the Early Jurassic period, c. 183 million years ago.
The Toarcian turnover was most strongly manifested in aquatic life forms, notably in mollusk groups like ammonites; its reach was global in extent, as evidenced by research in Japanese waters, the Andean basin, and the floor of the former Tethys Sea. Evidence points to anoxic bottom waters as the probable cause of these marine extinctions, linked in turn to the massive volcanism of the Karoo-Ferrar eruptions in the relevant era.
The Aptian extinction was an extinction event of the early Cretaceous Period. It is dated to c. 116 or 117 million years ago, in the middle of the Aptian stage of the geological time scale, and has sometimes been termed the mid-Aptian extinction event as a result.
It is classified as a minor extinction event, rather than a major event like the famous Cretaceous-Tertiary extinction event that brought about the end of the "age of dinosaurs" and the Mesozoic Era. The Aptian event is most readily detected among marine rather than terrestrial fossil deposits. Nonetheless, "The Aptian Extinction Event is an episode of importance, deserving a higher status among other minor events."
The Aptian event may have been causally connected with the Rahjamal Traps volcanism episode in the Bengal region of India, associated with the Kerguelen hotspot of volcanic activity. (At the time in question, c. 116-117 Ma, India was located in the southern Indian ocean; plate tectonics had not yet moved the Indian landmass into its present position.)
The Cenomanian-Turonian boundary event, also known as the Cenomanian-Turonian extinction event, the Cenomanian-Turonian anoxic event, and referred to in Europe as the Bonarelli Event, was the latter of two anoxic extinction events early in the Late Cretaceous period. The event occurred approximately 91.5 ± 8.6 million years ago, and brought about the extinction of the ichthyosaurs and pliosaurs. Although the cause is still uncertain, the result starved the Earth's oceans of oxygen for nearly half a million years, causing the extinction of approximately 27 percent of marine invertebrates. This global environmental disturbance increased atmospheric and oceanic temperatures. Boundary sediments show an enrichment of trace elements, and contain elevated 613C values.
One possible cause was sub-oceanic volcanism occurring approximately 500,000 years earlier. During that period, the rate of crustal production reached its highest level for 100 million years. This was largely caused by the widespread melting of hot mantle plumes under the oceans at the base of the lithosphere. This resulted in the thickening of the oceanic crust in the Pacific and Indian Oceans. This volcanism would have produced large quantities of carbon monoxide into the atmosphere, leading to global warming. Within the oceans, the emission of SO, H2S, CO, and halogens would have increased the acidity of the water, causing the dissolution of carbonate, and a further release of carbon dioxide. When the volcanic activity declined, this run-away greenhouse effect would have likely been put into reverse. The increased CO2 content of the oceans could have increased organic productivity in the ocean surface waters. The consumption of this newly abundant organic life by aerobic bacteria would produce anoxia and mass extinction. The resulting in elevated levels of carbon burial afterwards would accounting for the black shale deposition in the ocean basins.
65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The Cretaceous-Tertiary extinction event, which occurred approximately 65.5 million years ago at the end of the Maastrichtian, was a large-scale mass extinction of animal and plant species in a geologically short period of time. Widely known as the K-T extinction event, it is associated with a geological signature known as the K-T boundary, usually a thin band of sedimentation found in various parts of the world. K is the traditional abbreviation for the Cretaceous Period derived from the German name Kreidezeit, and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. With "Tertiary" being discouraged as a formal time or rock unit by the International Commission on Stratigraphy, the K-T event is now called the Cretaceous-Paleogene (or K-Pg) extinction event by many researchers.
Non-avian dinosaur fossils are found only below the K-T boundary, indicating that non-avian dinosaurs became extinct during the boundary event. A very small number of dinosaur fossils have been found above the K-T boundary, but they have been explained as reworked, that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct. Mammalian clades passed through the boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms.
Scientists theorize that the K-T extinctions were caused by one or more catastrophic events, such as massive asteroid impact(s) (like the Chicxulub impact), or increased volcanic activity. Several impact craters and massive volcanic activity, such as that in the Deccan traps, have been dated to the approximate time of the extinction event. These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology. Many researchers believe the extinction was more gradual, resulting from a combination of the events above and others including sea level and climate changes.
The start of the Eocene is marked by the emergence of the first modern mammals. The end is set at a major extinction event called the Grande Coupure (the "Great Break" in continuity) or the Eocene-Oligocene extinction event, which may be related to the impact of one or more large bolides in Siberia and in what is now Chesapeake Bay.
The transition between the end of the Eocene and the beginning of the Oligocene, called the Grande Coupure in Europe, occurring 33.9 ± 0.1 Ma, is marked by large-scale extinction and floral and faunal turnover (although minor in comparison to the largest mass extinctions). Badly hit were mammal populations in Europe, Asia, and the Americas who experienced a mass extinction, followed by a recovery. Most of the affected organisms were marine or aquatic in nature. They included the last of the ancient cetaceans, the Archaeoceti.
This was a time of major climatic change, especially cooling, not obviously linked with any single major impact or any major volcanic event. One cause of the extinction event is speculated to be volcanic activity. Another speculation is that the extinctions are related to several meteorite impacts that occurred about this time. One such event happened near present-day Chesapeake Bay, and another the Popigai crater of central Siberia, scattering debris perhaps as far as Europe. The leading scientific theory on climate cooling at this time is decrease in atmospheric carbon dioxide, which slowly declined in the mid to late Eocene and possibly reached some threshold approximately 34 million years ago.
The Middle Miocene disruption, alternatively the Middle Miocene extinction, refers to a wave of extinctions of terrestrial and aquatic life forms that occurred around the middle of the Miocene Epoch. The most extreme estimates assert that 30% of the mammalian genera of the early Miocene epoch went extinct.
The Middle Miocene Climatic Optimum (16 to 14 million years ago), considered generally to be the warmest period in Earth's history within the past 25 million years, saw a major shift in climate from global warming to cooling. The thoughts are that Columbia River volcanism likely triggered climatic cooling by sulphuric acid-induced volcanic winters, which would have increased the trade winds off West Africa and, in turn, fertilized the ocean by transporting more nutrients such as sulphates to the ocean.
Human bottleneck — as few as 55,000 members of genus Homo, including pre-human hominids like Homo erectus and Homo ergaster about 1.2m years ago. Could this be linked with the Yellowstone super volcanic eruption 1.3m years ago?
The last glacial period was preceded by 1000 years of the coldest temperatures of the Late Pleistocene, apparently caused by the eruption of the Mount Toba volcano. The six year long volcanic winter and 1000-year-long instant Ice Age that followed Mount Toba's eruption may have decimated Modern Man's entire population. During the Toba eruption, bottlenecks had existed amongst humans, chimpanzees, gorillas, cheetahs, rhesus macaques, orangutans and tigers. Genetic evidence suggests that Human population size fell to about 10,000 adults between 50 and 100 thousand years ago. The survivors from this global catastrophe would have found refuge in isolated tropical pockets, mainly in Equatorial Africa. Populations living in Europe and northern China would have been completely eliminated by the reduction of the summer temperatures by as much as 12 degrees centigrade.
Volcanic winter and instant Ice Age may help resolve the central but unstated paradox of the recent African origin of Humankind: if we are all so recently "Out of Africa", why do we not all look more African?
Because the volcanic winter and instant Ice Age would have reduced populations levels low enough for founder effects, genetic drift and local adaptations to produce rapid changes in the surviving populations, causing the peoples of the world to look so different today. In other words, Toba may have caused Modern Races to differentiate abruptly only 70,000 years ago, rather than gradually over one million years.
The Mount Toba eruption is dated to approximately 71,000 years ago. Volcanic ash from Mount Toba can be traced north-west across India, where a widespread terrestrial marker bed exists of primary and reworked air-fall ash, in beds that are commonly 1 to 3, and occasionally 6 meters (18 feet) thick.
Tambora, the largest known historic eruption, displaced 20 cubic kilometres of ash. Mount Toba produced 800 cubic kilometres. It was therefore forty times larger than the largest eruption of the last two centuries and apparently the second largest known explosive eruption over the last 450 million years.
Mount Toba's eruption is marked by a 6 year period during which the largest amount of volcanic sulphur was deposited in the past 110,000 years. This dramatic event was followed by 1000 years of the lowest ice core oxygen isotope ratios of the last glacial period. In other words, for 1000 years immediately following the eruption, the earth witnessed temperatures colder than during the Last Glacial Maximum at 18-21,000 years ago.
For the volcanic aerosols to be effectively distributed around the earth, the plume from the volcanic eruptions must reach the stratosphere, a height greater than 17 kilometres. Mount Toba's plume probably reached twice this height. Most solar energy falls at low latitudes between the Tropics of Cancer and Capricorn, so eruptions that happen near the Equator cause much more substantial cooling due to the reflection of solar energy. Toba lies 2 degrees north of the Equator, on the Island Sumatra.
The reduction in atmospheric visibility due to volcanic ash and dust particles is relatively short-lived, about three to six months. Longer-term global climatic cooling is caused by the highly reflective sulphuric acid haze, which stays suspended in the upper atmosphere for several years.
Ice core evidence implicates Mount Toba as the cause of coldest millennium of the late Pleistocene. It shows that this eruption injected more sulphur that remained in the atmosphere for a longer time (six years) than any other volcanic eruption in the last 110,000 years. This may have caused nearly complete deforestation of southeast Asia, and at the same time to have lowered sea surface temperatures by 3 to 3.5 degrees centigrade for several years.
If Tambora caused the "The year without a summer" in 1816, Mount Toba could have been responsible for six years of relentless volcanic winter, thus causing a massive deforestation, a disastrous famine for all living creatures, and a near extinction of Humankind.
About 50k years ago, climate change is linked with an extinction event.
Firestone and West believe that debris from a supernova explosion coalesced into low-density, comet-like objects that wreaked havoc on the solar system long ago. One such comet may have hit North America 13,000 years ago, unleashing a cataclysmic event that killed off the vast majority of mammoths and many other large North American mammals. They found evidence of this impact layer at several archaeological sites throughout North America where Clovis hunting artifacts and human-butchered mammoths have been unearthed. It has long been established that human activity ceased at these sites about 13,000 years ago, which is roughly the same time that mammoths disappeared.
They also found evidence of the supernova explosion's initial shockwave: 34,000-year-old mammoth tusks that are peppered with tiny impact craters apparently produced by iron-rich grains traveling at an estimated 10,000 kilometres per second. These grains may have been emitted from a supernova that exploded roughly 7,000 years earlier and about 250 light years from Earth.
"Our research indicates that a 10-kilometer-wide comet, which may have been composed from the remnants of a supernova explosion, could have hit North America 13,000 years ago," says Firestone. "This event was preceded by an intense blast of iron-rich grains that impacted the planet roughly 34,000 years ago."
In support of the comet impact, Firestone and West found magnetic metal spherules in the sediment of nine 13,000-year-old Clovis sites in Michigan, Canada, Arizona, New Mexico and the Carolinas. Low-density carbon spherules, charcoal, and excess radioactivity were also found at these sites.
"Armed with only a magnet and a Geiger counter, we found the magnetic particles in the well-dated Clovis layer all over North America where no one had looked before," says Firestone.
Analysis of the magnetic particles by Prompt Gamma Activation Analysis at the Budapest Reactor and by Neutron Activation Analysis at Canada's Becquerel Laboratories revealed that they are rich in titanium, iron, manganese, vanadium, rare earth elements, thorium, and uranium. This composition is very similar to lunar igneous rocks, called KREEP, which were discovered on the moon by the Apollo astronauts, and have also been found in lunar meteorites that fell to Earth in the Middle East an estimated 10,000 years ago.
"This suggests that the Earth, moon, and the entire solar system were bombarded by similar materials, which we believe were the remnants of the supernova explosion 41,000 years ago," says Firestone.
In addition, Berkeley Lab's Al Smith used the Lab's Low-Background Counting Facility to detect the radioactive isotope potassium-40 in several Clovis arrowhead fragments. Researchers at Becquerel Laboratories also found that some Clovis layer sediment samples are significantly enriched with this isotope.
"The potassium-40 in the Clovis layer is much more abundant than potassium-40 in the solar system. This isotope is formed in considerable excess in an exploding supernova, and has mostly decayed since the Earth was formed," says Firestone. "We therefore believe that whatever hit the Earth 13,000 years ago originated from a recently exploded supernova."
Firestone and West also uncovered evidence of an even earlier event that blasted parts of the Earth with iron-rich grains. Three mammoth tusks found in Alaska and Siberia, which were carbon-dated to be about 34,000 years old, are pitted with slightly radioactive, iron-rich impact sites caused by high-velocity grains. Because tusks are composed of dentine, which is a very hard material, these craters aren't easily formed. In fact, tests with shotgun pellets traveling 1,000 kilometres per hour produced no penetration in the tusks. Much higher energies are needed: x-ray analysis determined that the impact depths are consistent with grains traveling at speeds approaching 10,000 kilometres per second.
"This speed is the known rate of expansion of young supernova remnants," says Firestone.
The supernova's one-two punch to the Earth is further corroborated by radiocarbon measurements. The timeline of physical evidence discovered at Clovis sites and in the mammoth tusks mirrors radiocarbon peaks found in Icelandic marine sediment samples that are 41,000, 34,000, and 13,000 years old. Firestone contends that these peaks, which represent radiocarbon spikes that are 150 percent, 175 percent, and 40 percent above modern levels, respectively, can only be caused by a cosmic ray-producing event such as a supernova.
"The 150 percent increase of radiocarbon found in 41,000-year-old marine sediment is consistent with a supernova exploding 250 light years away, when compared to observations of a radiocarbon increase in tree rings from the time of the nearby historical supernova SN 1006," says Firestone.
Firestone adds that it would take 7,000 years for the supernova's iron-rich grains to travel 250 light years to the Earth, which corresponds to the time of the next marine sediment radiocarbon spike and the dating of the 34,000-year-old mammoth tusks. The most recent sediment spike corresponds with the end of the Clovis era and the comet-like bombardment.
If this theory is correct, a large comet detonated in the skies above North America, and rained fragments down across the whole region. The extreme temperatures would have ignited wildfires across the continent, destroying the vegetation that the large mammals needed to survive. Their death would then lead to a cascade of deaths by the large predators and the rest of the food chain that relied on them.
But on St. Paul Island, one of the Pribolofs 300 miles off the Alaskan coast, a small number of the six-ton behemoths apparently lasted an extra 3,000 years. (Indicating perhaps that the North American mainland fires didn't get them).
The comet might have also destabilized a large portion of the Laurentide ice sheet, causing a high volume of fresh water to flow into the ocean. Climate researchers believe this kind of event can disrupt the normal circulation of the ocean's flow, and lead to a global cooling event — a period of climate cooling that lasted 1,300 years, known as the Younger Dryas.
Meteorites thought to have triggered a cold snap that killed off early civilisation and giant animals
Scientists have found compelling evidence that a meteorite storm hit the earth more than 12,000 years ago, and is likely to have been responsible for the extinction of a prehistoric people and giant animals including mammoths. Evidence of the meteorite’s intense heat was found on two continents. The researchers believe the huge cosmic impact triggered a vicious cold snap, which caused widespread destruction.
The international team found a substance known as melt glass, which forms at temperatures of 1,7000 to 2,200 degrees Celsius and can result from a ‘cosmic body’ hitting the earth. The material was found in a thin layer of rock in Pennsylvania and South Carolina in the US, along with Syria. Tests confirmed the material was not of cosmic, volcanic or human-made origin.
‘The extreme temperatures required are equal to those of an atomic bomb blast, high enough to make sand melt and boil,’ said James Kennett, professor of earth science at UC Santa Barbara. The melt-glass appears identical to other material found in Meteor Crater in Arizona, and the Australasian tektite field, and also matches melt-glass produced by the 1945 Trinity nuclear air burst in New Mexico in the US, Professor Kennett said.
The team's findings support the controversial theory that an asteroid impact occurred 12,900 years ago and triggered the start of an unusual cold period on Earth, leading to widespread extinction of human and animal life. In the cold period, known as the Younger Dryas, North American megafauna including mammoths and giant ground sloths disappeared forever, along with a prehistoric civilisation called the Clovis culture. The Clovis people used distinctive bone and ivory tools and are regarded as the first human inhabitants of the New World.
Evidence supporting the theory has now been found on three continents, covering nearly one-third of the planet, from California to Western Europe, and into the Middle East. Syria is the easternmost site yet identified in the northern hemisphere, but the researchers have yet to find a limit to debris field of the impact. Melt-glass has been found in rock layers of the same age in Arizona and Venezuela. The three sites found in the latest study were separated by 1,000 to 10,000 kilometres, suggesting that ‘a swarm of cosmic objects,’ either fragments of a meteorite or comet, had hit the earth, Professor Kennett said.
Professor Kennett added that the archaeological site in Syria where the melt-glass material was found –– Abu Hureyra, in the Euphrates Valley –– is one of the few sites of its kind that record the transition from nomadic hunter-gatherers to farmer-hunters who live in permanent villages. ‘Archeologists and anthropologists consider this area the “birthplace of agriculture,” which occurred close to 12,900 years ago,’ Professor Kennett said. ‘The presence of a thick charcoal layer in the ancient village in Syria indicates a major fire associated with the melt-glass and impact spherules 12,900 years ago,’ he continued. ‘Evidence suggests that the effects on that settlement and its inhabitants would have been severe.’
Credit: Daily Mail.
During the last 50,000 years the global climate became colder and drier, reaching full glacial conditions 21,000 years ago. See Abrupt Climate Change.
The graph of the Vostok ice core data shows that the Ice Age maximums and the warm interglacials occur within a regular cyclic pattern, the graph-line of which is similar to the rhythm of a heartbeat on an electrocardiogram tracing. The Vostok data graph also shows that changes in global CO2 levels lag behind global temperature changes by about eight hundred years. What that indicates is that global temperatures precede or cause global CO2 changes, and not the reverse. In other words, increasing atmospheric CO2 is not causing global temperature to rise; instead the natural cyclic increase in global temperature is causing global CO2 to rise.
Today we are again at the peak, and near to the end, of a warm interglacial, and the earth is now due to enter the next Ice Age. If we are lucky, we may have a few years to prepare for it. The Ice Age will return, as it always has, in its regular and natural cycle.
Was it humans or climate change that caused the extinctions of the iconic Ice Age mammals (megafauna) such as the woolly rhinoceros and woolly mammoth? For decades, scientists have been debating the reasons behind these enigmatic Ice Age mass extinctions, which caused the loss of a third of the large mammal species in Eurasia and two thirds of the species in North America.
Now an extensive, interdisciplinary research team, involving over 40 academic institutions around the world and led by Professor Eske Willerslev's Centre for GeoGenetics at the Natural History Museum, University of Copenhagen, have tried to tackle the contentious question in the biggest study of its kind. And the answers are far more complicated than ever imagined.
The study, published online in the journal Nature reveals that neither climate nor humans alone can account for the Ice Age mass extinctions. Using ancient megafauna DNA, climate data and the archaeological record, the findings indicate dramatically different responses of Ice Age species to climate change and humans.
For example, the study shows that humans played no part in the extinction of the woolly rhino or the musk ox in Eurasia and that their demise can be entirely explained by climate change. On the other hand, humans aren't off the hook when it comes to the extinction of the wild horse and the bison in Siberia. Our ancestors share responsibility for the megafauna extinctions with climate change. While the reindeer remain relatively unaffected by any of these factors, the causes of the extinction of the mammoths is still a mystery.
Eske Willerslev says, "Our findings put a final end to the single-cause theories of the Ice Age extinctions, and suggests that care should be taken in making generalisations not just regarding past and present species extinctions but also those of the future; the impacts of climate change and human encroachment on species extinctions really depends on which species we're looking at."
However, Eline Lorenzen from the University of Copenhagen and lead author of the study says, "We do find that climate change has been intrinsically linked with major megafauna population size changes over the past 50,000 years, supporting the view that populations of many species will decline in the future owing to climate change and habitat loss."
Despite the unparalleled amount of data analysed in this study, the authors find no clear pattern distinguishing species that went extinct from species that survived, suggesting that it will be extremely challenging for experts to predict how existing mammals will respond to future global climate change.
Much of life on Earth gets regularly wiped out every 27 million years, according to boffins. It had been thought that this was caused by a dark star named "Nemesis", but apparently that was wrong. The next global-extinction event is due in about 16 million years' time.
The revelations are made in a new paper from palaeontologists Richard K Bambach of the Smithsonian Institution and astronomer Adrian Melott, flagged up by the Physics arXiv blog and viewable online here.
According to Bambach, there's no doubt at all that every 27 million years-odd, huge numbers of species suddenly become extinct. He says this is confirmed by "two modern, greatly improved paleontological data sets of fossil biodiversity" and that "an excess of extinction events are associated with this periodicity at 99% confidence". This regular mass slaughter has apparently taken place around 18 times, back into the remote past of half a billion years ago.
This had previously been noted by other scientists — though not confirmed so far back into the past — which had led to theorising on what could have caused such long-separated, regular disasters.
One theory which seemed to fit the facts was the "Nemesis", the idea that a huge, dark companion body orbits the Sun so far out that it comes near only on a 27 million-year cycle. At that point it ploughs into the Oort Cloud — the zone beyond the planets where comets spend most of their time — and causes a shower of comets to rain into the inner solar system, smashing up life on Earth.
Unfortunately, according to Melott, the very regularity of the extinctions means this can't be true. At various points in the last 500 million years the Sun has passed close enough to other stars that any Nemesis object would have had its orbit significantly affected, so that the sequence of disasters on Earth should have changed interval.
The two boffins write:
"We confirm the originally noted feature in the time series for extinction. However, we find that it displays extremely regular timing for about 0.5 Giga-years. The regularity of the timing compared with earlier calculations of orbital perturbation would seem to exclude the Nemesis hypothesis…"
According to the handy chart furnished by Bambach and Melott above, one can see that the apocalypses don't exactly run like a Swiss watch. The mass die-offs (circled peaks) are usually pretty close to the vertical dotted lines showing the 27 million-year time tick, but they can easily be a few million years off either way.
They aren't universally fatal, either: the last one saw less than ten per cent of all species then alive wiped out.
If nobody manages to work it out, and provided that humanity doesn't meanwhile become disembodied minds, depart in an interstellar exodus or get wiped out early in some kind of unscheduled disaster, we'll eventually find out by observation what the underlying cause is. The next dotted line is due in 16 million years, but the associated extinction could be as much as 10 million years early.
J. John Sepkoski, Jr., is a professor of paleontology at the University of Chicago; he is also one of the co-discoverers of the apparent cyclic nature of mass extinctions. Here is his take on the status of his controversial idea:
"The question of a 26 million-year periodicity of extinction generated considerable interest in the 1980s. David Raup, now professor emeritus at the University of Chicago, and I arrived at this hypothesis empirically, based on our statistical analysis of data from the fossil record. The best information on extinction rates comes from a compilation of 36,000 marine animal genera from the past 600 million years. I continue to update and improve this compilation.
"The fossils show a statistical variation in extinction rates having a period of approximately 26 million years. The two periodic peaks of extinction after the Cretaceous-Tertiary boundary, 65 million years ago, are at the end of the Eocene (roughly 37 million years ago) and in the Middle Miocene (about 17 million years ago).
"Raup and I had initially performed a coarser analysis of the fossil record, focusing on extinctions at the family level (one level above genus in the taxonomic hierarchy). That analysis conformed to a 26 million-year periodic series, but it was missing two beats: one in the late Middle Jurassic (170 million years ago) and one in the Early Cretaceous (95 million years ago). Our hypothesis predicted that more extensive data offering finer time resolution would reveal that small extinction events occurred at those times. Indeed, the better, more voluminous genus-level data subsequently confirmed the prediction.
"Why has interest in this hypothesis subsided? There are two reasons. First, there are statistical questions about extinction rates that just cannot be answered. It is not clear whether other hypotheses can fit the empirical data as well as does the hypothesis of periodicity. The distribution of extinction events in time is certainly not random, but there is more than one way to analyse the data. Does the fact that the data appear to fit well to a model of periodicity mean that the events truly are periodic? This question was debated throughout the late 1980s without reaching a resolution
"The second reason for the loss of interest is one not uncommon to science: Here is an intriguing observation that no one knows how to explain. Researchers formulated a number of very interesting astronomical hypotheses to account for the 26 million-year periodicity of extinction. The most famous of these was the Nemesis, or 'death star,' hypothesis, which stated that the sun has a distant companion whose highly elliptical orbit brings it into the Oort Cloud (a swarm of frozen comets orbiting far from the sun) once every 26 million years. During each pass through the Oort Cloud, the companion's gravity would scatter huge numbers of comets, some of which would crash into Earth. The environmental damage caused by these impacts would lead to an elevated rate of extinctions.
"Nemesis has not been found, although Richard A. Muller of the University of California at Berkeley continues to track dim red stars to discover if one of them might be a companion to the sun. Also, evidence of impact (such as iridium-rich clay layers or widespread shocked minerals) has not been found in association with all the major extinctions, as would be predicted by the hypothesis. There is excess iridium at the end-Triassic (208 million years ago) and Late Eocene events, as would be expected if impact occurred then, but no such evidence is seen at other events in the periodic series that have been studied in detail.
"Hence, we have an empirical observation of periodicity but no new hypotheses that suggest interesting tests. This situation is not conducive to scientific effort or to intellectual curiosity, so interest in the question of periodic extinctions has died down. But not completely: there is an interesting scientific paper on the problem published by M. R. Rampino and B. M. Haggerty in Earth, Moon, and Planets (Vol. 72, Nos. 1-3, pages 441-460; 1996), entitled "The 'Shiva Hypothesis': Impacts, Mass Extinctions, and the Galaxy."
Solar System's "Bouncing"
A new computer model of our solar system's movement relative to the Milky Way indicates that it "bounces" up and down through the plane of the galaxy. As the solar system circles around the galaxy, it also bobs up and down through the galactic disc roughly every 60 million years, straying some 200 light years to either side.
Writing in the Monthly Notices of the Royal Astronomical Society, the scientists at the Cardiff Centre for Astrobiology that built the computer model say that during certain periods in the bounce, gravitational forces from surrounding gas and dust clouds could dislodge comets from their paths. These comets could then plunge into our solar system, some of them colliding with the Earth.
The Cardiff team says that when we pass through the galactic plane every 35 to 40 million years, the chances of a comet collision are increased tenfold. Intriguingly, evidence from craters on Earth also suggests we suffer more collisions approximately every 36 million years. "It's a beautiful match between what we see on the ground and what is expected from the galactic record," noted Cardiff's Professor William Napier.
Napier contends that the periods of comet bombardment also coincide with mass extinctions, such as that of the dinosaurs 65 million years ago. But while the bounce effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe."This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale," commented Centre director Professor Chandra Wickramasinghe. And in case you're interested in when the next comet infestation might occur, our present position in the galaxy suggests we are now very close to another such period.
Our Galaxy and the Solar System
For billions of years, Earth has been on a perilous journey through space. As our planet whirls around the sun, the whole solar system undertakes a far grander voyage, circling our island universe every 200 million years. Weaving our way through the disc of the Milky Way, we have drifted through brilliant spiral arms, braved the Stygian darkness of dense nebulae, and witnessed the spectacular death of giant stars.
Many of these marvels may well have been deadly, raining lethal radiation onto Earth's surface or hurling huge missiles into our path. Some may have wiped out swathes of life, smashed up continents or turned the planet to ice. Others may have been more benign, perhaps even sowing the seeds of life.
Today, the solar system travels a near-circular path around our galaxy, keeping a constant 30,000 light years between us and the seething galactic core. We once assumed most stars stayed in such quiet orbits for their entire lives. Our ride may have been more exciting. The characteristic spiral arms of a galaxy such as the Milky Way are waves of higher density, regions where stars and gas are a little closer together than elsewhere in our galaxy's disc. Their additional gravity is normally too weak to alter a star's path by much, but if the star's orbital speed happens to match the speed at which the spiral arm is itself rotating, then the extra force has more time to take effect.
It is theorised that our Sun is part of a twin-star system and the twin is a "brown" star (a star that has extinguished) named Nemesis (called Vulcan in ancient times). This star is on a fatalistically orbit that, at it's closest point, comes close enough to enter into our planetary system — this happens every 25-30 million years. Its mass is 56 percent of the mass of the Sun.
Our Solar system, in concert with the Sun, is revolving around companion star, a "brown" star. They are moving in tandem with one another along a flat, elliptical orbital plane that, at it's closest point, can come close enough to enter into our planetary system. Distance of closest passage roughly corresponds to the distance of the orbit of Pluto from Sun. It's estimated to orbit the Sun with a period slightly less than 5000 years.
The twin star's orbit takes it through the Oort cloud on the outward and inward journeys.
The Oort cloud is a spherical cloud of comets which may lie roughly 51,000 AU (510 billion miles), or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Oort cloud is thought to comprise two separate regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud. Objects in the Oort cloud are largely composed of ices, such as water, ammonia, and methane. Astronomers believe that the matter composing the Oort cloud formed closer to the Sun and was scattered far out into space by the gravitational effects of the giant planets early in the Solar System's evolution.
On it's inward journey, the twin star can knock comets from the Oort cloud towards our planetary system. It can also impact into the comet cluster too.
"Theories about a huge new planet in deep space are based on a hypothesis by astrophysicists John Matese and Daniel Whitmire at the University of Louisiana at Lafayette. They theorize that the gravitational influence of a planet they have named Tyche (Ty-kee), up to four times the mass of Jupiter, may be responsible for sending comets from a region in space called the Oort Cloud toward Earth. Tyche is also believed responsible for the unusual orbit of the dwarf planet Sedna, a planetoid discovered in 2003 that travels from 7 trillion to 92 trillion miles from the sun during its travels. The period of Tyche’s alleged orbit — 27 million years — has also been linked to theories about mass extinctions on Earth credited to comet impacts.
"The new planet Tyche is a variation on a theory proposed in 1984 that a distant companion to the sun — a cold, brown dwarf star dubbed “Nemesis” — may account for comet activity. Tyche, if it exists, is estimated to orbit the sun at 15,000 times the distance at which Earth orbits. Tyche may have escaped detection until now because at that distance the planet would not radiate heat or reflect light. Whitmire said that Tyche is probably a huge ball of condensed hydrogen and helium with a colourful, banded surface similar to Jupiter. Tyche is also likely to have moons."
Comet Cluster Orbit
A comet cluster is in orbit around our solar system that orbits every 3,600 years.
The Grand Cycle
The Grand Cycle, or Grand Year, is the timing of a complete revolution of the Earth's axis. A complete revolution takes place once every 25,850 years and is called "Precession of the Equinoxes" — see Timings.
Some believe the 13th Grand Cycle starts on 17 Dec 2013
Biblical prophecies speak of a period of terror and chaos followed by calm, and then, unexpectedly, amidst seeming overwhelming peace and renewal and prosperity, the end.
There do seem to be cycles of catastrophes — see my investigation into Timings — and they coincide with the earth's axis slowly changing direction.
A good book to read is Perilous Planet Earth: catastrophes and catastrophism through the ages by Trevor Palmer.
Earth's "smaller year" of 2,150 years (which is the time the sun takes to retrograde one entire sign of the Zodiac) is suspected of being the timing of great catastrophes. I will try to gather information about them here to see if science echoes the myth. If we postulate 1950 as being the change date then working back in steps of 2150 years produces:
Although there are traumatic events to coincide with the "smaller year" occurrences, there are many other events too. Admittedly the "smaller year" events seem to be the larger ones.