WIPEOUT: NEXT ROUND IN THE PERMO-TRIASSIC MASS EXTINCTION DEBATE

A major catastrophe 251 million years ago left life teetering on the brink of oblivion. Now for the first time we have a clear picture of what caused it, says leading palaeontologist Michael Benton

251 MILLION years ago, at the end of the Permian period, life on Earth was almost completely wiped out by an environmental catastrophe of a magnitude never seen before or since. All over the world complex ecosystems were destroyed. In the sea, coral reefs, fishes, shellfish, trilobites, plankton, and many other groups disappeared. On land, the sabre-toothed gorgonopsian reptiles and their rhinoceros-sized prey, the dinocephalians and pareiasaurs, were wiped out forever. Only 5 per cent of species survived the catastrophe, and for the next 500,000 years life itself teetered on the brink of oblivion. What terrible event could have wrought such havoc?

Two theories have been proposed -the impact of a huge meteorite or comet over 10 kilometres in diameter, or a massive and prolonged volcanic eruption. Up to now the evidence has been equivocal. But the data has been accumulating over the past 10 years, and the picture is now clear enough to say with some certainty what happened.

An impact might seem a tempting model. A massive catastrophe demands an extraordinary explanation -something unexpected, something from outer space. And we know that impacts can cause mass extinctions. It seems that the dinosaurs and many other groups of animals and plants were wiped out 65 million years ago by the impact of a huge meteorite in modern day Mexico. The crater has been found, there is good evidence for the shock wave, and for the fa1lout rocks and dust all round the world. In February 2001, a team of scientists claimed they had found clear evidence that the mass extinction at the end of the Permian was also caused by a meteorite impact. Luanne Becker of the University of Washington in Seattle and her colleagues from NASA and other institutions announced in a paper in Science (Vol291, p 1530 ) that they had found extraterrestrial helium and argon in rocks from the Permo-Triassic boundary in China and Japan.

The gases were trapped inside the fullerenes or buckyballs that are often associated with impact debris. When Becker and her team looked closely at the helium and argon they found isotope ratios like nothing else on Earth, but similar to those found in meteorites. On this basis they argued that the fullerenes -and their entrapped gases -must have come from an impact.

The claim was splashed all over the press. On 23 February 2001, The New York Times reported "Meteor crash led to extinctions in era before dinosaurs". The Times said, "Asteroid collision left the world almost lifeless".

But later in 2001, several learned journals published critiques in which other geochemists tried and failed to replicate Becker's results. Other samples from the same boundary bed in China apparently contained no buckyballs, argon or helium, and a Japanese geologist, Yukio Isozaki of the University of Tokyo, pointed out that the Japanese sample came from a rock formation that didn't even include the Permian-Triassic boundary.

But Becker and her team still stand by their results. They repeated their analyses from the Chinese samples, and confirmed the helium result. They also have support from an independent source. ln September 2001, Kunio Kaiho ofTohoku University in Japan reported that sediment grains from Permo-Triassic boundary sections in China show evidence of compression by impact, as well as geochemical shifts indicative of a huge impact -though his data is far from conclusive.

All in al1, the evidence for an impact at the Permo-Triassic boundary is limited when compared with the mass of evidence for an asteroid hit at the end of the Cretaceous: the iridium anomaly (a worldwide spike in the abundance of iridium, an element derived from meteorite impacts); shocked quartz (grains showing evidence of high-pressure modification); glassy spherules (melt particles derived from sedimentary rocks); and above all an enormous crater of the correct age. The discovery of a Permian equivalent of any of these could confirm the impact theory at any moment. But for now, most geologists do not accept the impact model for the crisis at the end of the Permian.

Instead, their attention has focused on Earth-bound processes. The idea is that massive volcanic eruptions, sustained over half-a-million years or more, caused catastrophic environmental deterioration -poison gas, global warming, stripping of soils and plants from the landscape, eruption of gases from their frozen locations deep in the oceans, and mass deoxygenation. The evidence for this version of events is compelling compared with the impact hypothesis.

First and foremost, the end of the Permian was indeed characterised by huge volcanic eruptions. The remains of these are preserved in the Siberian Traps, a vast accumulation of basalt lavas some 3 million cubic kilometres in volume and covering 3.9 million square kilometres of what is now eastern Russia.

Precise dating of the Siberian Traps shows that they span the boundary between the Permian and the Triassic, with the eruptions beginning perhaps 500,000 years before.

The Siberian Traps were not formed by explosive eruptions from classic cone-shaped volcanoes. More commonly, basalt is erupted through fissures, long cracks in the ground, as happens on Iceland today. Such eruptions last for a long time, and the lava bubbles up in huge volumes, spreading sideways from the fissure. They are accompanied by prodigious outpourings of gases, mostly carbon dioxide.

The effect of these gases was devastating. The full story of the havoc they wrought is written in the sedimentary rocks that span the Permo-Triassic boundary. Until the 1990s, geologists had to rely on incomplete or hard-to-date sections in northern Italy, Pakistan and Afghanistan. Reputedly excellent sections in southern China were not available to overseas geologists, mainly for political reasons. Nothing daunted, British geologists Tony Hallam of the University of Birmingham and Paul Wignall of the University of Leeds obtained a modest travel grant from the Royal Society, and went to China in 1991. What they found amazed them : the rock record was complete, and it told the story of the crisis millimetre-by-millimetre as they worked their way through the rocks from bottom to top.

Hallam and Wignall focused on sections around the Meishan township. Working up through the succession, the last rocks deposited in the Permian were limestones containing diverse and abundant fossils, such as foraminiferans (microscopic shelled protozoans), brachiopods (lamp shells), and conodonts (jaw elements from primitive fish-likevertebrates). Rarer fossils include cephalopods (coiled molluscs that are distant relatives of the modern squid and octopus), sea urchins, starfish and small crustaceans called ostracods, all typical of warm, shallow seas. Near the top, there is extensive burrowing in the limestones, indicating conditions of full oxygenation. Clearly, life at this time was diverse and abundant.

Then, suddenly, everything changes. The thick, burrowed limestones disappear, and with them the abundant fossils. The limestone is capped by a mineral-rich layer containing lots of pyrite -a classic marker of very low atmospheric oxygen. On top of this are three layers of limestone, mudstone and clay, encompassing about half a million years. These layers, numbered as beds 25, 26 and 27 in the Chinese system, tell how the crisis unfolded, so let's look at them in more detail. The oldest layer, bed 25, is a thin band of pale-coloured clay 5 centimetres thick in which fossils are very rare, just a few foraminiferans and conodonts. Under the microscope, this clay contains small iron-rich pellets and decayed pieces of quartz that indicate it was formed from an acidic ''tuff'', an amalgam of volcanic fragments and ash from an explosive volcanic eruption -presumably the Siberian Traps. The next bed up, number 26, consists of 7 centimetres of dark, organic-rich limey mudstone in which fossils are slightly more abundant-there are brachiopods, clams and cephalopods. Based on the relatively diverse fossils, and on geochemical evidence, oxygen levels during deposition of bed 26 were low but not anoxic.

Together, beds 25 and 26 form a distinctive dark-on-light marker band that has been detected elsewhere in China, which is useful for geologists who wish to make correlations from location to location. This "ash band" has been detected so far in 12 provinces throughout China, covering at least a million square kilometres. Whatever created it was extremely far-reaching.

Bed 27 indicates some degree of environmental recovery. The 17-centimetre-thick layer of limestone is full of burrows, so bottom conditions were not especially low in oxygen. The lower part of the bed contains occasional Permian brachiopod fossils near the base. Near the top, the conodont Hindeodus parvus appears for the first time: this is the globally accepted marker for the beginning of the Triassic period. (Geological boundaries are marked by the appearance of fossils, not their disappearance. The major event happened at the base.of bed 25, but no significant new species appeared until the middle of bed 27.) What does it all mean? One of the stories the Meishan section tells is of a dramatic extinction event. In the late l990s, Jin Yugan and his colleagues from the Nanjing Institute of Geology and Palaeontology, and Doug Erwin from the National Museum of Natural History in Washington DC, undertook a huge sampling programme. They found that at the base of bed 25, 116 marine species suddenly disappeared, representing 94 per cent of the total. Then, in the following 500,000 years stretching to the top of bed 27, new species appear then disappear with alarming speed. Overall a further 45 species dropped out, one at a time.

Clearly something terrible happened at the base of bed 25 and its ramifications continued for half a million years. But what exactly happened? Fortunately, the Meishan rock section, and other sections elsewhere, contain a record of environmental changes through the Permo- Triassic crisis, in the form of isotopes of oxygen and carbon. Both elements have two stable, naturally occurring isotopes whose ratios fluctuate depending on environmental conditions. The isotope ratios are locked into the skeletons of organisms during their lifetimes, so careful recordings from the shells of bivalves or foraminiferans, for example, can give a detailed picture of atmospheric and oceanic conditions through time.

Oxygen isotopes are used as a palaeothermometer. Oxygen occurs in two forms, oxygen-16 and oxygen-18. These are incorporated into the calcite skeletons of marine creatures at differentrates depending on the water temperature, more oxygen-18at low temperatures, and more oxygen-16 at high. At the base of bed 25, the main mass-extinction level, there was a sudden shift in the oxygen isotope ratios indicating a worldwide rise in temperature of 6C. This may not sound much, but it would have a profound effect on the world's ecology. Climatologists have been getting very excited recently about a half-a-degree rise in global temperatures. The carbon isotopes suggest what might have caused the temperature increase. They show a massive shift towards the light isotope, carbon-12, exactly at the time of the big extinction. Pulses of carbon-12 in the geological record are usually indicative of a volcanic eruption or a large die-off (plants, animals and bacteria concentrate carbon-12 in their bodies and release it when they die). Both certainly happened at the end of the Permian.

But the carbon-12 pulse is far too big to be explained by these mechanisms alone. Calculations of global carbon budgets have suggested that, even if every plant, animal, and microbe died and was buried; altogether they would only account for about one-fifth of the observed carbon shift. The Siberian Traps would have added another fifth. Where did the remaining three-fifths come from?

The extra carbon-12 was probably buried, frozen deep under the oceans in the form of gas hydrates. These are extraordinary accumulations of carbon-12-rich methane locked up in cages of ice at very high pressure. If the atmosphere and oceans warm up sufficiently, these gas reserves can suddenly melt and release their contents in a catastrophic way. The explosion of gas through the surface of the oceans has been termed a "methane burp". A very large methane burp at the end of the Permian could have produced enough carbon-12 to make up the deficit. The cause of the burp was probably global warming triggered by huge releases of CO2 from the Siberian Traps. Methane is a greenhouse gas too, so a big burp raises global temperatures even further. Normally, long-term global processes act to bring greenhouse gas levels down. This kind of negative feedback keeps the Earth in equilibrium. But what happens if the release of methane is so huge and fast that normal feedback processes are overwhelmed? Then you have a "runaway greenhouse". This is a positive feedback system: excess carbon in the atmosphere causes warming, the warming triggers the release of more methane from gas hydrates, this in turn causes yet more warming, which leads to the release of more methane and so on. As temperatures rise, species start to go extinct. Plants and plankton die off and oxygen levels plummet. This is what seems to have happened 251 million years ago. The effects were profound and long-lasting. In the Meishan section, the Permo-Triassic boundary in bed 27 is followed by a succession of dark limestones and shales containing sparse fossils. This seems to represent a post-apocalyptic world; in which CO21evels were still very high and the oceans and atmosphere were starved of oxygen. The 6 per cent of species that survived the initial onslaught were struggling. Normal recovery processes had not yet kicked in. When oxygen levels fall, plants and photosynthesising plankton in the sea normally replenish it by absorbing excess CO2 and generating oxygen. After the crash at the end of the Permian, perhaps oxygen levels had been driven so low, and so much of plant life had been killed, that this was impossible.

The surviving species were a very poor sample of what had lived before: thin-shelled molluscs that required very little food and swam languidly over the black, deoxygenated muds, and the "living fossil" Lingula in its shallow burrows. Near the end of the Permian period, each region of the world had its own fauna and flora. Afterwards, the survivors became cosmopolitan. It took 20 or 30 million years for coral reefs to re-establish themselves, and for the forests to regrow. In some settings, it took 50 million years or more for full ecosystem complexity to recover. Geologists and palaeontologists are only just beginning to get to grips with this most profound of crises.

Michael Benton is head of the Department of Earth Sciences at the University of Bristol. His book on the end-Permian crisis, When Life Nearly Died, has just been published by Thames & Hudson, price 16.95

Some interesting points to ponder in this article.

Mythology is fascinating for the themes forwarded.

Many theories as to what generated the end of the ice age..and saw water levels rise hundreds of feet by 9,500 BCE.

So the end of the Tertiary period ,something...some mechanism.

A comet?...the break up of the Tertiary moon?

somthing catastrophic haunts man from this time...he witnessed and survived it..passed the experience on.

We look back and try to piece together the stories of Atlantis..or other cultures swallowed up as per hints from Mayan Codex's...hints from ancient Egypt..the Ande's.

On my part..there is definitely a "Tertiary something"....man is still working thru the Global Amnesia from its occurance.

Fire, Flood, and Famine, (Chapt.4, 'Demonology and Disaster', By Hugh Soar (a brief summary) cont.

Recurrent theme in most mythologies is that of chaos. It starts as the lore of a tribe's mythical history, or forerunner of the religious epics of the land, as the case of Biblical Genesis; since we know chaos myths to follow a pattern, the Biblical creation myth would appear incomplete. The following chaos myth, perhaps one of the most perfectly preserved, is taken from Revelations 6-12. It has a reference I think, to the earlier catastrophe, the disintegration of the Tertiary Satellite, though it may be contrasted with the myth immediately following it, also taken from revelations (16-2) which apparently refers to a capture cataclysm. "And I beheld when he had opened the sixth seal, and lo there was a great earthquake; and the sun became black as sackcloth of hair; and the moon as blood; and the stars of the heaven fell into the earth, even as a fig tree casteth her untimely figs, when she is shaken of a mighty wind. And the heaven departed as a scroll when it is rolled together; and every mountain and island were moved out of their places. And the kings of the earth, and the great men, and rich men, and the chief captains, and the mighty men, and every bondsman, and every freeman, hid themselves in the dens, and in the rocks of the mountains. And said to the mountains and rocks. Fall on us, and hide us from the face of him that sitteth on the throne and from the wrath of the lamb. For the great day of his wrath is come, and who shall be able to stand."

"And the seventh angel poured out his Vail into the air.. and there were… thunders and lightning's; and there was a great earthquake, such as not since men were upon the earth, so mighty an earthquake, and so great. And the great city was divided into three parts, and the cities of the nation fell, and great Babylon (Atlantis?) came in remembrance before God… and every island fled away, and the mountains were not found. And there fell upon men a great hail out of heaven, every stone about the weight of a talent."

According to Jewish Lore there was, at the end of every age, a war between God and his adversaries. The enemy, significantly was conceived to be in the form of a dragon. Anti-Christ, this mysterious force, was considered to be influenced by Satan, though this influence we shall see to be, in reality the transposition of evil from an unknown force, only dimly conceived, to a known Prince of Evil. Anti-Christ the latent force of evil, is the Moon. Satan, the Ruler of the Kingdom of darkness whom St. Paul describes in fact as the God of his Age, (in contrast to an age to come after the day of judgement, (the Day of Jahweh)-the moonless age), is ominipresent, and since Satan is held, either directly or indirectly responsible for all evil, when the Moon commences its breakdown, or when its closer in relation to the earth enables its association with the cataclysm, the emphasis of evil will sharply turn from the abstract and by this time fully symbolized Satan to the material, dominant, satellite. The conception of ages, sharply defined, each ending in chaos, and each commencing under the potency of a God is not of course unique. The religion of the Aztecs, of which Tezcatlipoca was but one God/Age, and that of India, the Avataras of Vishnu, are important examples. The moonless age, the age when life will spring from the earth anew, is the time of happiness, until it too is presently dominated by another satellite. One thinks of the Norse Lif, and Lifthrasir entering hand in hand the world, after the terrors of Ragnarok. This played a great part in chaos myths with the dragon also looming.

Edward Langton feels a great connection between Assyria/Babylonian myth, and Satan, since, in the Jewish Apocryphal literature, (Revelations. 12.9) Satan is identified with the dragon that storms the heaven. According to Persian teachings, the serpent Azi-Dalakar is bound and fettered in the Mountain of Damavand. Arriman, the evil principle of Zoroastrian dualism and early monotheism released him after 9,000 years, but , after another thousand years he was slain, by Keresaspa. After the cleansing of the world, the serpent, it is said, will disappear. Here we seem to have an account of the fettering (by bonds of gravitational attraction) of a satellite, a common enough motif in many mythologies, (The fettering of Fenris for example). Evil follows Good, as we know from the study of many religions.

On Satan, it is a coincidence that he, and Azazel the 'chief of the watchers' and the leader of the fallen angels are both associated with the dragon, the destroyer of the world, and referred to as an arch-fiend. As Lord of the Material Universe, 'God of this Age', if he were to be associated with the newly captured moon, and regarded as responsible for the destruction consequent upon the capture cataclysm, then his relation to the conception of God, becomes clearer, The coming of Satan (or Anti-Christ) is the event which disrupts the normal course of life. He is the destroyer, and as has convincingly been shown, the appellation 'dragon' is perfectly consistent with the newly captured moon. We do see also the wolf becomes a part of this moon association with the dragon? From Webmaster-When the Moon in its phases goes to is furthermost points it is often called the Head of the Dragon moon and the Tail of the Dragon moon as if it were talking about some comet, and may explain the alchemical serpent biting its tail, or is Benzine Lunar based? The Head-Tail was based on a larger scale of the North Pole Serpent, and at times is mixed with this age or problem.

The knowledge of these myths came to Wales by way of Hu Gadarn and the Avanc to those Lake names presently. The most compelling myth is Ragnarok:

"After the Fimbul winter, the terrible trail of snow an all embracing ice, the Giantess Angur-boda fed the progeny of the fettered wolf, Fenris until, pursuing Sol and Mani (The Sun and Moon-Egyptian form), they overtook and devoured them. At the chaotic disaster the whole earth shook, and the stars fell from their places in the heavens. (Note the Revelations similarity in Bibles line). The author goes on with the myth, but the point is these Biblical Revelation's already happened and the land was re-peopled. Could St. John merely borrowed from other tales of something already written and spoken in terms of the past, is St. John saying history is repeating, or was he wishing for man a doom what had already happened before? The Celtic story of Henny-Penny is from this line of above works. The Polynesians of the Maori have a strange variation on these myths of the three destruction's of earth. The 'second upsetting of the land was followed by 'Hapopo' (decay) folding up the sun'. Puta, the spirit responsible for the first turning over of the land (agriculture or not?), has been equated with Buddha (more likely Ptah, Egyptian God), and it is thought that the evidence exists for a culture borrowings by the Polynesians from India (and Egypt). India has many accounts of earth being turned upside down. The deluge tradition from the Windward Islands follows the general pattern, but includes a reference to falling stones. "The groves of trees and the stones were carried away by the winds… There they watched, nights ten, the sea ebbed, and they too saw the little heads of the mountains…The land remained without produce…The wind was becoming feeble…the stones and the trees began to fall from the heavens…They heard with terror the loud voice of the falling stones.' A Fijian creation myth recorded, tells how Tangaloa, when the earth was yet uninhabited, sent his daughter Turi to the earth in the shape of a snipe to find place to create humans (sounds like Noah's doves, or ravens?). She eventually found a place where she could rest, and the myth tells of her repeated flights to Tangaloa as she reported that the dry surface was extending upon all sides. Tangoloa then sent down earth and a creeping plant to cover bare rock. The plat grew, withered, decomposed, and the worms which appeared, became human beings." Popul Vuh provides the last example of chaos/flood myth. The first men that were made were made of mud, but they were unsatisfactory to the forefathers so they were broken up, and destroyed. The second men were created, were created of wood, and they populated the earth. But they did not remember their creator, they walked aimlessly about on all fours. So Huracan, the Heart of Heaven, the creator, sent a great flood which fell upon the heads of those wooden creatures and annihilated them. They were deluged by a heavy resin, which fell from the sky. The face of the earth was darkened and a black rain fell (obsidian like, ash, or asteroid?), by day and by night. The following sequence I think is unique in this type of myth; the animals, the birds and beasts of the stockyard, and even the household implements rise and abuse these men. Finally, the men fled in terror to the housetops, and the trees, and even the caverns. But even these refused them access. The descendants of these wooden men are said to be monkeys.

One point of irony involves the men made of mud and then wood, how interesting the mummies of S. America Pacific coast recently found are made of these materials. Is this a commentary of a practice that of the cult of the dead that by the time it reached the Popul Vuh (A Book of the Dead) it was so remote that they considered these people as old as the monkeys? The walking on fours seems to imply that they some how knew our ancestors of the 'walking on fours' larger humanoids may have not quite died out in the memory of these regions?

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