The End Permian Mass Extinction
By: Grant Erickson
Think of a world which existed 290 million years ago. As you look out over the
terrain in front of you, you would think that you are on an alien planet. You see
volcanoes spewing ash and lava. Beside them is the ocean which is swarming with many
different species of echinoderms, bryozoans and brachiopods. As you look down onto
the sea floor you are amazed at the countless number of starfish and urchins. Some
animals you can’t even describe and you have no idea even what phylum they belong to.
This is a world at its height in diversity of oceanic species. Millions of wondrous species
existed at this time in the ocean and most of them will never appear again in Earth’s
history. In the blink of an eye things now look vastly different. The sky is dark. Oceans
are no longer teaming with life. The stench of sulfur, rotting flesh, and plants hangs in
the air. The ground trembles under your feet. You feel an intense heat burning your face.
You look up and see one of the greatest show of force mother nature has ever shown.
Whole mountains are being thrown in the air. Lava and debris are everywhere. You ask
yourself, what has happened? Will life ever exist on earth again?
The above maybe what the end of the Permian period could have looked like.
Marine life was devastated, with a 57% reduction in the number of families (Sepkoski,
1986) and an estimated 96% extinction at the species level (Raup, 1979). Oceanic life
suffered the most but terrestrial life forms were also greatly affected. There was a 77%
reduction in the number of tetrapod families (Maxwell and Benton, 1987). All major
groups of oceanic organisms were affected with the crinozoans (98%), anthozoans (96%),
brachiopods (80%) and bryozoans (79%) suffering the greatest extinction (McKinney,
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1987). The end of the Permian and beginning of the Triassic periods marked the single
greatest extinction event the world has ever faced.
There are many questions regarding the speed of the extinction at the end of the
Permian. Was the event a catastrophe or gradual? There is evidence for both scenarios.
Some of the evidence supports an extraterrestrial event such as a meteor hitting the earth.
Other evidence supports the theory that the ocean and terrestrial environments slowly
changed.
The research done by Xu Dao-Yi and Yan Zheng (1993) gives evidence for an
extraterrestrial event.
They studied the distribution of carbon 13, iridium, and
microspherules across the P/T (Permian and Triassic) border. The section was over 35
cm thick. They found a sudden depletion in C-13 falling from a value near zero to a
minimum of less than –6% in some samples. This indicates an abrupt shift of carbon
isotope compositions across the P/T boundary of all marine carbonate profiles of the
investigated sections in China and the turning point from positive to negative lies at the
boundary itself. These results confirm the catastrophic character of the PTB (Permian
Triassic boundary). Similar patterns of C-13 change have been observed in more than
five P/T sections in China. Other scientists like Baud et al (1989) argue that this anomaly
is the result of a depositional hiatus or erosional disconformity. Xu and Yan argue that
there is no evidence for a significant hiatus and that Baud et al. (1989) even made a
mistake in the timing of their rock layers. “If the PTB is considered a catastrophic event,
a short-time hiatus should be expected and is in fact a reasonable consequence of a
catastrophic event” (Dao-Yi and Zheng, 1993). But what is the significance of C-13
being associated with catastrophic events? Hsu et al. (1982) suggested that carbon
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isotope anomalies are related to microplankton productivity. We will touch again on this
later in the paper.
Therefore, the sudden C-13 change may indicate the exact
stratigraphic position of the mass killing event at the PTB. Analysis of iridium (Dao-Yi
and Zheng, 1993) in the layer showed some interesting results. High Ir values only
occur in the uppermost part of the layers. This means that the layer is close to the PTB.
The concentration of Ir was at least an order of magnitude higher than the background
values and this is characteristic of most Upper Permian and Lower Triassic boundaries.
The scientists go on to say that “the existence of a rich Ir anomaly on a global scale
within the K/T boundary layers of both marine and continental facies has been interpreted
as highly impressive evidence for an impact origin.” Another discovery that may serve
as a marker of an event is microspherules. A variety of microspherules have been
discovered in the PTB layers of the Meishan section which is located in China (Dao-Yi et
al., 1989). The origin of the microspherules could be multiple. They can be created by
the intense heat and pressure within the Earth’s crust or my a meteor impact. There is
also evidence that volcanoes may produce microspherules. Microspherules are small
circular indentations in the rocks and the most abundant elements are Si or Si-Al.
Mircospherules are similar to cosmic dust. Since a large amount of microspherules
occurs in a thin layer of PTB layer it can serve as another event marker.
Maxwell (1989) who got his information from Clark et al. (1986) said that
The elements in boundary clays across China suggest that there is
a remote possibility that the predominantly illite boundary clay resulted
from the alteration of ejecta dust from a comet impact, but the most likely
source was ash from a massive volcanic eruption.
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The trace elements suggested that the dust was highly acidic and the ratios of TiO
and AlO are low enough to support the volcanic dust scenario (Clark et al. 1986).
There is some research which gives evidence of a gradual extinction event.
Magaritz et al. (1988) reported that carbon-isotope ratios are known to shift or
change at some boundaries associated with a mass extinction event. A shift can
occur due to a decrease in plant production following a meteor impact or from a
large decrease in sea level that reduces shelf area, exposing the shelf and its
accumulated organic carbon to erosion. There are sections examined in the Alps
of Italy and Austria that actually show a gradual change in the C-13 content of
marine organisms across the PTB. These sections show no dramatic shifts that
can be associated with a mass extinction. Thus as you can see, the findings of
Clark et al. (1986) and Magaritz et al. (1988) shows geochemical evidence that
the mass extinction was a gradual event and not a catastrophic extinction event.
Faunal evidence is much harder to come by and explain than geochemical
evidence due to the lack of PTB boundary layers. Also marine faunal evidence is much
more linear than terrestrial. This means that the marine layer was created at a much more
constant rate that the terrestrial layer and thus provides us with greater amount of data to
work with. Yoram Eshet et al. (1995) said that fungal evidence can be used to mark the
PTB layer. It can also be used for evidence to show how the extinction event occurred.
There is a sharp fungal spike in the PTB layer which is made up of Lueckisporites
virkkiae, Endosporites papillatus, and Klausipollenites schaubergeri spores. Yoram
Eshet et al. (1995) defined four stages across the Permian-Triassic boundary. Stage one,
consisted of low abundance of spores which became increasingly abundant. At the top,
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the disappearance of more than 95% of the Late Permian pollen and spore taxa became
apparent. Stage two contained and abundance of fungal remains and here it is defined as
the “fungal spike”. Also there is quite a bit of organic detritus, composed of carbonized
plant debris. Stage three and four occurred after the boundary and will not be discussed.
Since this fungal evidence can be seen throughout the world it makes it highly unlikely
that the increase is everywhere an artifact resulting from sedimentary processes or local
conditions. Also it should be noted that the fungal spike is very thin which suggests that
remains could have been missed at many PTB layers. The reason there is a large fungal
spike should be obvious.
Fungi are known to adapt and respond quickly to
environmental stress and disturbance (Harris and Birch, 1992). During a high stress
period, like an extinction event, decimation of autotrophic life occurs which creates a
large pool of decaying organic matter. This is evident by the abundant plant debris seen
in the fungal spike.
Marine evidence for the PTB extinction event provides us with the best and most
complete evidence of the event. According to Douglas H. Erwin (1993), the world’s
leading expert on the Permian crisis, marine organisms such as bivalves and gastropods
suffered such a great loss that most are unfamiliar even to students of invertebrate
zoology.
But findings by Erik Flugel and Joachim Reinhardt (1990) contains
contradictory evidence that marine life suffered in the end Permian and early Triassic. It
is commonly assumed that reefs are affected more severely at major extinction events
than other biotopes. Another assumption is that there is a decrease in diversity of
shallow-marine organisms during the Late Permian. In analyzing the Permian-Triassic
reefs they found that there was no reduction in diversity of reef organisms during the last
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part of the Permian. Instead, there was evidence of high, and even increasing diversity of
the uppermost Permian reef communities. The argument of Erik Flugel and Joachim
Reinhardt (1990) was again countered by a number of scientists. Sweet (1992) showed
that strata previously assigned to the topmost Permian stage was mistaken and that the
strata should have been moved lower. If Sweet’s scheme is accepted, then the mass
extinction becomes an intra-Triassic event. The differences in data could be due to
inadequate sampling as proposed by Sepkoski (1986). The basis for this statement is that
virtually no complete late Permian sections and complete sections across the PTB layers
have been found. This argument is quite weak. Sweet’s theory is based on the validity of
his dating techniques. So far all dating techniques use methods which extend information
of how elements and compounds behave today into the past, hoping that they behave in
the same way but there is no evidence for that.
As you can see, nothing is certain in the study of the Permian-Triassic extinction
event. Since there is conflicting evidence of when, what, and how the extinction event
occurred, there will be will be many different theories and hypothesis on the causes of the
end Permian extinction. This paper will explore a few of the possibilities.
There are many theoretical causes of the Permian mass extinction. The causes are
divided up into two main groups: diversity dependent and diversity independent.
Diversity dependent hypotheses are new and are not very popular with many scientists
but they do make sense.
Diversity-dependent factors limit population growth as
population size get larger. It involves a depletion of environmental factors such as
oxygen, nitrogen, and carbon dioxide. Bramlette (1965) and Tappan (1968) evolved on a
scenario of nutrient reduction. In the model, landscapes where flat and thus streams were
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not capable of transferring nutrients to the oceans. Also a reduction of upwelling activity
helped the effect. They also proposed that oxygen levels may have declined as a result of
a loss of primary productivity.
Tappan went on to say that heavy extinction of
suspension feeders at the end of the Devonian, Permian, and Cretaceous implicated
changes in primary productivity as the main cause of the extinction through accumulation
of organic material in the ocean and thus starving the ocean and land of nutrients.
Remember that the oceans would starve if there was no upwelling.
Through this
mechanism the end Permian is very gradual and it would selectively remove different
species at different times. Many scientists criticize this mechanism because it would
cause the oceans to be virtually sterile. Wingnall (1993) criticized this hypothesis by
saying “It appears unlikely that the oxygen-deficiency was induced by high productivity
for, as we have shown, organic-rich facies are only patchily developed in the
Griesbachian (early Triassic).” When thought through carefully, nutrient accumulation or
sequestration would have reached a peak during the development of the extensive
Carboniferous coal swamps and not during the Permian period.
One very interesting hypotheses is based on biogeography. Erwin (1993) said
that,
Since most species occur only within a single marine province, one of the
major controls on global diversity should be the number of marine provinces.
Similar communities in different areas of a single province tend to have roughly
similar community composition (at least for the more abundant species). Thus the
species within a nearshore sandy-bottom community will tend to recur throughout
a province but will differ between provinces.
Since continents usually define marine boundaries then when continents are dispersed
there will be more marine provinces and thus more diversity. Erwin goes on to say that
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the formation of Pangea (the great super-continent) in the late Permian times forced a
reduction in sea-floor spreading.
Since the depths of the ocean basins are a function of the age of oceanic
crust, a reduction in the rate of sea-floor spreading will allow the mean age of the
oceanic crust to increase, increasing the size of the ocean basins. The volume of
the mid-ocean ridge spreading centers will also decline. The net effect should be
a regression.
Richard Leakey (1995) adds an interesting parallel.
Imagine four one-inch squares, each of which has a total edge length of
four inches, giving a grand total of sixteen inches. Now bring them together as a
single square of side two inches. The total edge length is now a mere eight
inches, just half of the previous figure. The same thing happens with individual
continents and available shallow-water habitats. The formation of Pangea
therefore must have devastated species in these habitats by this mechanism
alone……
Regression causes in increase in the continent’s surface area and it also alters climate
patterns. There will be an increase in seasonality in nearshore waters along with an
increase in nutrients and competition as provinces merge together. Therefore global
diversity should be at its lowest when the supercontinent exists. The more continental
climates and higher seasonality will increase the instability of nutrients, primary
productivity, and other trophic resources. Here species that are affected seasonally will
be affected greatest while species with a broad trophic and environmental tolerances will
be favored. Since the study of instability is very complex we should treat these kinds of
hypotheses carefully. The above factors may well have played a role with other factors in
causing the greatest extinction on the earth (Erwin, 1993).
Now we move away from diversity-dependent factors to diversity-independent
hypotheses which are more common and accepted. This involves models that affect all
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individuals of a species equally and is independent of the number of species present. As
mentioned before, most extinction fall into this category.
Extraterrestrial phenomena is one of the favorite explanations for the Permian
extinction. There is quite a bit of evidence to support it. Monastersky (1993) reported on
well-preserved Permian shales and cherts from northeastern British Columbia. These
formed when the region lay at the bottom of an inland basin. The researchers isolated
from the rock small amounts of kerogen.
Kerogen is the decomposed residue of
plankton. At the PTB the kerogen records drop sharply in the ratio between heavy C-13
atoms and light C-12 atoms. Monastersky goes on to say
To interpret the shift in Carbon isotopes, the researchers exploited the fact
that plants tend to avoid Carbon 13 as they grow during photosynthesis. Because
of the vast number of phytoplankton competing for carbon-12 during normal
times, however, the plants typically incorporate some carbon-13. But a sudden
die-off of most phytoplankton would give survivors greater access to carbon-12.
When they fall to the ocean floor and get incorporated into sedimentary rocks,
they reduce the ratio of carbon-13 to carbon-12 within a rock….
Geochemists who have studied inorganic carbon which came from shells of ancient
plankton have also detected abrupt drops in carbon isotopic ratio at the end of the
Permian. Due to the many factors that can alter this ratio they have not been able to
isolate what caused the change. Fewer processes affect the carbon isotopic ratio in
kerogen.
This greatly strengthens the case that the surface ocean suffered from a
biological crisis.
“It is consistent with some sort of catastrophic event like an
asteroid….”(Monastersky, 1993). Richard Monasterky (1997) reports that Gregory J.
Retallack found “shocked” quartz at two sites in the Antarctica and one site in Australia.
This type of quartz is riddled with intersecting sets of fractures and is born only during
impacts.
Iridium also adds to the evidence. Scientists now know that an impact is
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associated with the extinction at the Cretaceous-Tertiary boundary and that there is also
an increase in Iridium at this boundary. The discovery of a significant increase in iridium
and microspherules at the PTB boundary by Dao-Yi et al. (1993), Dao-Yi et al (1985),
Dao-Yi et al (1989) gives numerical evidence of an impact.
There are many problems with the impact theory. First there is evidence that
shows that the Permian extinction started gradually and had a more rapid pulse at the end
(Monastersky, 1993). Also some scientists have argued that the quartz crystals found by
Retallack were not shocked because Retallack only studied them under a light
microscope, where it is difficult to distinguish shock features from more prosaic
deformations caused by normal tectonic stress in the Earth’s crust. Monastersky (1997)
said that “an impact capable of triggering unparalleled losses should have strewn telltale
clues around the world.” Western geologists have attempted and failed to verify the
Chinese reports of iridium. Anomalies can cause a build up of iridium in one place
which would lead to what the Chinese have discovered (Erwin, 1993).
Hatfield and Camp (1970) found a crude correlation between the galactic position
of the solar system and major faunal extinctions. They said that if the Earth moved
through a galactic plane (one which extreme radiation passes through) it would subject
the Earth to huge amounts of radiation and magnetic fields. This could cause breeding
patterns in some animals to stop or be altered. Hatfield and Camp (1970) goes on to
show how this is possible. Our galaxy has one revolution around the galactic center
every 200 million years. At the same time the sun completes three vibrations which are
perpendicular to the galactic plane. Thus there is one vibration about every 80-90 million
years.
Therefore Hatfield and Camp (1970) speculated that when the Earth moves
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through the plane, it could produce a faunal extinction like the Permian extinction. The
increased radiation would produce an increase of mutations and deaths in some species.
Species that live deep in the ocean and lakes would not be affected directly. Erwin
(1993) using information from many studies said that “an increase an increase in cosmic
radiation would have eliminated many groups and increased the rate of mutation among
the survivors, thus explaining both extinction and the subsequent radiation.”
This
statement makes some sense when one thinks about how all of the new species were
created so fast during the Triassic era. Dickens (1992) supported the theory of cosmic
radiation. He said that the cause for extinction could be changes in the planetary or
galactic system; change in the angle of the Earth’s axis; changes in the atmosphere,
probably as a result of magmatic and volcanic activity; or a combination of these factors.
There is good evidence to reject this proposal. Cosmic radiation will affect terrestrial and
very shallow organisms more than benthic organisms. Evidence suggests that both
benthic and shallow organisms were greatly reduced and terrestrial organisms were not as
affected as oceanic species.
The cosmic radiation model can not explain these
differences.
Before much study was done on the mechanics of mass extinctions some people
believed that the Permian extinction was due to global cooling or ice age conditions.
This is not the case. There is no evidence to support the fact that there was global
cooling at the end of the Permian. On the contrary, there is major evidence which
support the theory that warm climates existed. As you will see, most of the theories are
based on global warming. Dickens (1992) gives evidence of glaciation in the upper
Carboniferous and it is widespread in the lowest stage of the Permian. Above the lower
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Permian there is no evidence for glaciation. “After the mid-Permian, world climate
became steadily warmer until in the latest Permian and earliest Triassic a universally hot
climate, substantially warmer than the present prevailed” (Dickens, 1992). Warm waters
are indicated by the development in the sedimentary sequence of reefs, desert deposits,
fine-grained red beds, and evaporites.
The hot climate of the latest Permian and earliest Triassic, together with
marine regression, widespread volcanism, and tectonic instability, would have
subjected the fauna and flora to extremely rigorous conditions and would no
doubt have been sufficient to effect a great change in the biota (Dickens, 1992).
Detailed studies about the causes are lacking according to Dickens but more likely
causes for climatic change may be fluctuations in cosmic radiation and solar
energy.
The hypothesis that a salinity decrease caused the mass extinction of oceanic life
was first formed by Beurlen in 1956 (Maxwell, 1989). Evidence for this phenomena was
based mainly on stenohaline groups such as the bryozoans, ostracodes and corals which
were greatly reduced at the PTB. The least affected groups were gastropods and fresh
water fishes.
Organisms with some tolerance of salinity variations survived and
proliferated in the early Triassic. Therefore it was thought that a selective extinction of
marine families occurred in the PTB. Beurlen proposed that salinity was progressively
reduced during the second half of the Permian and also that salinity reached critically low
values at the PTB, before persisting into the early Triassic. Early marine faunas are
sparse and many groups that were diverse before and after the PTB are not present at the
PTB. Beurlen said that this was due to a few places in the world where normal salinities
were maintained. A return to normal salinities world-wide would allow the surviving
species to repopulate the seas and as a result, crop up again in the fossil record after their
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temporary absence. This leaves us with one main question, what would cause such a
large reduction in ocean salinity? Maxwell (1989) gives some answers based on the work
of many scientists. In the 1950’s and 60’s it was thought that the drop in salinity was due
to large-scale evaporite sedimentation accompanied by the formation of large quantities
of dense brine which was stored deep down on the sea floor. Salinity could have been
reduced to a value around 30 parts per thousand (which is safe to drink). If this occurred
than the result would be huge volumes anhydrite, gypsum, salt, and halite deposited on
the sea floor. Beurlen (Maxwell, 1989) estimated that 5*10^14 tones would need to be
deposited. Other scientists strongly criticized Beurlen stating that this would only be
15% of the amount of evaporites that would need to be stored. A figure of 200,000 cubic
kilometers was postulated but some scientists say that this is only 10% of the real
amount. Therefore it would seem that Permian evaporite deposits can not explain the
lowering of salinity levels. The best reason that I could find to explain salinity decreases
was put forward by Fisher (1963) called the brine-reflux hypothesis. The evaporation of
sea water and the deposition of salts produced dense brines which sank deep onto the
floor of the ocean. This leaves the top circulating water free of salt. I think Fisher would
come into opposition with the scientists that say the extinction was due to a temperature
decrease. A temperature decrease would cause less evaporation and should cause the
oceans to be saltier due to fresh water being accumulated in glaciers.
Erwin (1993) said that a scientist named Bowen in 1968 actually argued that
Permian climates triggered an increase in Permian salinity of approximately 20% above
today’s levels. His study was based on the volume if massive Louann salt deposits from
the Gulf Coast and other Paleozoic evaporites. So as you can see there is a great deal of
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uncertainty if even salinity had anything to do with the PTB extinction. Erwin goes on to
slam all of the hypotheses.
These salinity hypotheses are instructive examples of how often
“explanations” are nothing of the kind. Stenohaline taxa are also largely
stenotopic, and often independent evidence must be advanced that salinity
changes were the selective factor. Contrary to several of these papers, nautiloids
did not particularly suffer during the extinction, blastoids and crinoids
disappeared long before the ammonoiads or the brachiopods, and “strophomenid”
brachiopods suffered far greater extinction did spiriferid brachiopods… In
summery, none of these patterns is consistent with the salinity hypothesis.
If you look back through the geological column, you will find a correlation between
marine regressions and major mass extinction’s. But what really is the connection?
Erwin gives use a good base from which we can conclude many new things. His
statements are based on MacArthur and Wilson’s theory of island biogeography.
They suggested that species diversity on an island is a function of
immigration to the island from a continental source, and extinction on the island is
due largely to competition. Thus the immigration rate should be a declining
function of the number of species on the island and should approach zero when all
the species from the source pool have reached the island. Similarity, as species
diversity increases, the extinction rate should climb as competition for resources
increases. The equilibrium species diversity will be the point where the
immigration rate and extinction rate are the same. Among the implication of the
theory are that smaller islands and more distant islands should have fewer species
than larger islands or those closer to the source area” (Erwin, 1993).
Evidence for a regression is quite good according to Maxwell (1989).
1. The greatest level of regression of shallow seas from continents of any
Phanerozoic interval occurred at this time.
2. Reef environments are unknown during the latest Permian and early Triassic.
3. There are few taxa up to class level of early Triassic benthic and pelagic
organisms, contrasting with large numbers before and after this time.
4. Early Triassic taxa were organized into small number of shelly invertebrate
communities with very low species diversity.
5. Biogeographic diversification was a Phanerozoic low in the early Triassic.
6. There are abundant late Permian evaporite deposits.
Using the species-area hypothesis we can deduce several facts. We already know that
during the PTB the sea level declined and that one single continent was formed. This
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reduces shelf area and thus reduces the area a species can live in causing greater
competition for resources.
You will then get species dying off and lower species
diversity. Some scientists claim that a reduction of shelf area alone would have cause the
extinction. Since most organisms on land are connected to the sea, we can postulate that
there would also be a reduction in the number of species on land.
Many scientists, as reported by Erwin, have rejected the species-area hypothesis.
Their rejection is based on many facts. Some point to an example during the Middle
Eocene where there was a 50% reduction is shelf area along the Gulf Coast. According
to the species area hypothesis there should have been a reduction in diversity of species
but evidence supports that there wasn’t. Some argue that it is only the change in number
of marine provinces that affects diversity. To me it would seem that there if there is a
reduction in species area there should be a reduction in marine provinces are at least the
area of space to live in each province. Erwin (1993) makes some very challenging
suggestions.
If the species-area relationship is valid, regressions should have a far
greater effect on continents than on islands since, in general, the area of an island
will increase during a regression. Modern tropical reef biotas are among the
richest environments in the world, rivaling if not surpassing the tremendous
diversity found in tropical rain forests.
If most marine families have
representatives on oceanic islands they will be relatively immune to regressioninduced extinction.
Anoxia-stagnant ocean hypothesis was first presented by Berry and Wilde (1978).
To me this is one of the most complicated and intriguing hypothesis which tries to
explain the mass extinction. Berry and Wilde based their theory and conclusions on their
research of the extensive black shales of the Paleozoic which indicate that the oceans
were depleted of oxygen. Oceans now have a minimum zone of oxygen at middle
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depths.
As you descend down further oxygen levels increases.
The Berry-Wilde
hypothesis replaces this with an anoxic deep ocean. While this fact alone does nothing to
enhance our knowledge of the extinction, combining it with the isotopic record of carbon,
oxygen, and sulfur and the various explanations for shifts in isotopes and we can generate
a good number of hypotheses based on global anoxia and global warming (Erwin, 1993).
We will examine a couple of these hypotheses individually.
The first explanation proposed that there was a regression which caused exposed
organic materials to be oxidated and this resulted in a drop of C-13 levels and an increase
in carbon dioxide. The erosion and oxidation of organic compounds caused an increase
in surface temperature about six degrees centigrade. Since warm water can hold less
“air” or oxygen than cold water, the increase in temperature caused a drop in the
solubility of oxygen in seawater. This compounded that fact that the oceans were already
depleted of oxygen due to the long-term oxidation of carbon. Thus an anoxic ocean
caused the mass extinction of ocean species and this also affected terrestrial species.
A second model based on Erwin (1993) is a little different. The core of the
hypotheses is that there was a regression then the formation of the anoxic layer. There
was a rapid transgression which resulted in the spread of anoxic waters which resulted in
extinction. There is quite a large body of evidence to support this theory. The early
Triassic communities were low in diversity but species abundance was very high. This is
characteristic of opportunistic expansion in an environmentally stressed setting.
Laminated black shales are lacking which indicate anoxic conditions. This means that
most of the Earth did not have anoxic conditions which supports a regression. This
theory also suggests that a fast extinction occurred and not a gradual one. As with all
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theories there doubters.
The most damaging piece of evidence is that biota was
decimated prior to the onset of the transgression.
There is also evidence in some
sediments that there was extensive bioturbation. This is a characteristic of oxygen rich
waters (Erwin, 1993).
The third and last model, which is based on the evidence of C, O, and S isotopes
sets up the ocean into two boxes. The upper box which represents shallow oxygen rich
waters while the lower box and far larger portion represents the lower ocean which is
anoxic.
The two are separated by a redoxcline which causes minimal interchange
between them. Supporters of this hypothesis argue that the transition between these two
states occurred at the PTB.
It involved a rapid destratification of the oceans and
establishment of vigorous circulation. It resulted in the oxidation of deep carbon that had
been stored previously. This resulted in the increase in atmospheric carbon dioxide and
sulfur but a decrease in oxygen and C-13. This is supported by evidence in layers in the
Eastern Tethys. Most importantly, the oxidation of nitrogen and phosphorous induced
marine extinction by nutrient deficiency. Terrestrial extinction’s were the result of a drop
between 10 and 90 % in oxygen and probable climate cooling (Erwin, 1993). A paper
written by Tom Waters (1996) tried to explain how anoxia might have caused the
particular patterns that the extinction’s took. His paper was based on a stagnant ocean so
that there was little flow from the deep to shallow regions. As dead organisms rained
down from the surface into this nearly stagnant water, the decay of all that material
gradually sucked the oxygen out of it. With few currents flowing into the deep, there was
no way to bring fresh oxygen from the surface. While oxygen disappeared, carbon
dioxide was building up in the Permian deep. The deep ocean they argue was a disaster
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waiting to happen. What finally unleashed it was a cooling climate. The cooling was the
result of a decrease in atmospheric carbon dioxide which weakens the greenhouse effect.
This chilled surface waters, sending them down and pushed up the anoxic waters into the
shallow areas. It killed marine life and the carbon dioxide which escaped from the water
warmed the atmosphere melting the glaciers causing a transgression. There is evidence
that during the Neoproterozoic Era, from 800 to 543 million years ago, that this same
thing happened four times.
The survivors were the active breathers who could flush out the excess
carbon dioxide. For instance, passively respiring corals suffered heavy losses in
the Permian extinction, while active breathers like snails and clams fared much
better (Waters, 1996).
Thus species with higher extinction rates were the ones less able to handle carbon
dioxide poisoning.
There is good evidence that volcanism may have been a factor in the PTB
extinction. A paper by Paul R. Renne et al (1995) puts together numerous papers into
one sound thesis. The evidence of a bolide impact and for volcanism were synchronous
within several hundred years. Thus more scientists believe in the volcanism theory rather
than an asteroid simply because there is more evidence for volcanism and also that
volcanism can produce some of the effects of an asteroid collision with earth which can
eliminate the asteroid hypothesis all together. Erwin (1993) stated four ways in which
volcanism might be able to cause mass extinction’s.
1.
Creation of a dust cloud that reduces photosynthesis and initiates global
cooling; injection of massive amounts of carbon dioxide and sulfates into the
atmosphere into the atmosphere causing global warming.
2.
Creating acid rain as the sulfate is converted to sulfuric acid and reducing the
protective ozone shield.
3.
Creation of a thermal anomaly
4.
Injection of poisonous trace elements into the atmosphere and oceans.
19
The Siberian traps represent the most voluminous known continental flood
voluminous known continental flood volcanism in Earth’s history, with an
original volume estimated at 2,000,000 to 3,000,000 cubic kilometers distributed
over 2,500,000 kilometers square in central Siberia. The traps’ volcanic
succession overlies Permian strata and is in turn overlaid by Triassic strata…..
(Renne et al. 1995)
When Ar-40/Ar-39 and U-Pb dating is done on the volcanic rock, the age turns out to be
250 Ma (plus or minus 1.6 Ma). Many other dating techniques have been used and they
all roughly agree on this date. Many scientific papers such as Wingnall et al. (1993),
Dao-Yi et al. (1993), Dao-Yi et al. (1989), Dao-Yi et al. (1995), and Erwin (1993) and
the papers they used give irrefutable evidence of volcanism. Therefore there is scientific
proof that a great volcanic event occurred during the PTB. But how could the volcanoes
in Siberia have produced such an unprecedented global extinction. Wignall (1993) give a
short hypothesis on this subject.
...we suggest that the effect of huge volumes of carbon dioxide released
during the eruption of the Siberian flood basalts may have led to global warming,
which in its turn produced extensive areas of warm saline bottom waters poor in
oxygen. The major negative swing of carbon isotopes in the early Griesbachian
could be recording this major volcanogenic input of isotopically light carbon.
Renne et al. (1995) gives his interpretation.
Siberian flood volcanism, perhaps augmented by sulfates derived from
evaporites of the Siberian platform, could have produced sufficient stratospheric
sulfate aerosols for rapid global cooling to ensue. Resulting ice cap accumulation
likely caused the dramatic marine regression, which in turn led to subaerial
exposure of the continental shelves. This latter effect would account for the
ubiquitous anomalies in C, S, and Sr isotopes. Isotopically light C and S from
mantle-derived carbon dioxide and sulfur dioxide would also contribute to the
observed negative anomalies in C-13 and S-34. Ice storage effects plus enhanced
erosion of the continental crust could have produced the seawater O-18
enrichments observed at the boundary. Rapid transgression after the boundary
would follow from the abrupt cessation of Siberian volcanism and the resulting
ice cap recession. Climate recovery may have been enhanced by slower
developing greenhouse effects of volcanogenic gasses, primarily carbon dioxide.
Indeed, a short-lived volcanic winter, followed within several hundred thousand
years by greenhouse conditions, would fully explain the environmental extrema
that caused the P-T mass extinction’s.
20
Erwin (1993) showed that over long periods of time, carbon dioxide can act as an
insulator and initiator for a greeenhouse effect. A release of carbon dioxide from the
Deccan Traps flood basalts in India may have been the main cause of the end-Cretaceous
mass extinction. If the volume of the eruptions are correct, sulfate aerosols and carbon
dioxide may have been introduced during the formation of the Siberian Traps. The
buildup of carbon dioxide in the atmosphere would warm the earth and cause a decrease
in pH of the ocean. An estimated 5*10^18 moles of carbon was produced during the age
of the Deccan Traps and the same thing could have occurred during the Permian.
In both modern and Cretaceous oceans the upper 100m of the ocean is
reasonably well buffered against pH changes by calcareous microplankton, but
the release of this large volume of carbon dioxide would have swamped the
system and lowered the pH of the waters, perhaps triggering carbonate
dissolution. A reduction in the biomass of the calcareous microplantion could
have established a positive feedback loop, further increasing carbon dioxide
buildup in the oceans and the atmosphere. During the Permian, calcareous
microplankton did not exist, although calcareous algae were abundant until the
onset of the regression. Consequently, the buffering system might not have been
as well developed as it was by the Cretaceous. Thus the effects of increased
atmospheric carbon dioxide may have been more severe (Erwin, 1993).
There is little evidence and research done on trace element poisoning. The only
reason this theory exists is the parallel between the extinction and chemical disasters in a
large interconnected water system.
But as Erwin (1993) points out, Permian and
terrestrial floras and faunas were not affected by trace element poisoning because the
marine environments at that time had a slow diffusion rate. The high concentration of
some trace elements could be due to a regression and high level of marine extinction’s
which reintroduced potassium, phosphate, vanadium, and other biogenic elements into
seawater and sediments.
21
The situation facing us is like a court room where all the witnesses eliminate one
another as suspects. We are left with two option. Either a person that we don’t know of
committed the crime or all the witnesses are guilty. The problem facing the judge is like
the one facing us. Some suspects can be eliminated immediately such as global cooling,
species-area effects and extraterrestrial impact. But most of the other hypotheses are
open as possibilities. We can pick one cause and say that it caused the extinction but
what do we do with evidence that the hypothesis doesn’t support? People prefer a simple
and uncomplex explanation for the extinction but they will not have their wish. The
evidence of the Permian extinction supports many complex theories. The extinction can
not be traced to a single cause, but rather a multitude of events occurring together. The
start of the extinction seemed to have been caused be a regression. The regression was
due to a decrease in ocean currents so carbon dioxide could build up in the deep. This
caused a decrease in atmospheric carbon and a cooling of the earth. The regression
caused :
1.
Reduction in habitat diversity
2.
Increase in climatic seasonality
3.
Oxidation of organic material
4.
Gas hydrate release
The reduction in habitat diversity and increase in climatic seasonality caused ecological
instability. Oxidation of organic material and gas hydrate release caused an increase in
carbon dioxide which lead to the development of an anoxic ocean and global warming.
Adding to the global warming and anoxic ocean was the Siberian Traps which produced
22
carbon dioxide and metal deposits. These three main factors: ecological instability,
anoxic ocean, and global warming caused the greatest extinction the earth has ever had.
"An analysis of the fossil record reveals some unexpected patterns in the origin of
major evolutionary innovations, patterns that presumably reflect the operation of different
mechanisms" (Lewin, 1988). The most interesting "unexpected pattern" is the gross
asymmetry between the diversification of life in the Cambrian explosion (about 440
million years ago) and that following the great end Permian extinction (a little over 200
million years ago). Biological innovation was intense in both instances; both biological
explosions burst upon a life-impoverished planet. Many niches were unoccupied. Even
so, all existing (and many extinct) phyla arose during the Cambrian explosion and none
followed the Permian extinction. "...why has this burst of evolutionary invention never
again been equaled? Why, in subsequent periods of great evolutionary activity when
countless species, genera, and families arose, have there been no new animal body plans
produced, no new phyla?" (Lewin, 1988). Some evolutionists blame the asymmetry on
the different "adaptive space" available in the two periods. "Adaptive space" was almost
empty at the beginning of the Cambrian because multicellular organisms had only begun
to evolve; whereas after the Permian extinction the surviving species still represented a
diverse group with many adaptations. (Just how the amount of "adaptive space" available
was connected to the "mechanism" doing the innovation is not addressed in this paper.)
Scientists contemplating these matters, however, seem to concur that microevolution,
which supposedly gives rise to new species, cannot manage the bigger task of
macroevolution, in particular the creation of new phyla at the beginning of the Cambrian.
23
In an attempt to summarize the material learnt and as a strong believer in God I
strongly feel that the truth needs to be told.
And it came about after seven days, that the water of the flood came upon
the earth. In the six hundred year of Noah’s life, in the second month, on the
seventeenth day of the month, on the same day all the fountains of the great deep
burst open, and the floodgates of the sky were opened….Then the flood came
upon the earth for forty days; and the water increased and lifted up the ark, so that
it rose above the earth. And the water prevailed more and more upon the earth, so
that all the high mountains everywhere under the heavens were covered. The
water prevailed fifteen cubits [one cubit = 18 feet (New American Standard Bible,
1977)] higher, and the mountains were covered. And all flesh that moved on the
earth perished, birds and cattle and beasts and every swarming thing that swarms
upon the earth, and all mankind; of all that was on the dry land, all in whose
nostrils was the breath of the spirit of life, died. Thus He blotted out everyliving
thing that was upon the face of the land, from man to animals to creeping things
and to birds of the sky, and they were blotted out from the earth; and only Noah
was left, together with those that were with him in the ark (New American
Standard Bible, 1977).

To completely understand nature we must first realize that there is a God. When
we look at the evidence of the extinction at the PTB in the context of a world wide flood,
while also realizing that pre-flood conditions could be different than our own, it doesn’t
contradict the theories put forward.
Obviously with a flood there was a great
transgression and regression. Differences in cosmic radiation were dramatic when you
compare pre-flood with post-flood conditions (if you believe that the earth was
surrounded by water). Differences in isotopes readings and all other measurements agree
with the flood setting when you accept that pre-flood conditions could be different than
ours. Elements and compounds could have decayed at different rates and occurred at
different concentrations. To say that say that one thing behaves in a certain way now it
must have behaved in the same way in the past is wrong. The Permian crisis was the
greatest extinction event to ever have occurred on Earth. Without having this kind of
24
understanding of Earth’s events, scientists will never find a correct answer to what
happened and will forever be groping in the darkness in search for the truth.
25
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