Precursor to KT - Species in decline?
Many scientists believe around ten million years
before the KT boundary, the environment began to
get markedly more hostile to life. The lush coastal
planes on which dinosaurs depended began to turn
arid, as sea levels fell worldwide. Their natural
habitat was disappearing. Between ten million and
three million years before the KT boundary, the
dinosaurs seem to have suffered a huge decline.
One interpretation of the fossil record is that forty
percent of dinosaur species went extinct before the
In an interview with the BBC, David Archibald,
Professor of Evolutionary Biology at San Diego
State, spoke of the period leading up to the
ARCHIBALD: “ Organisms are adapted for a
certain type of environment and when those
The KT mass extinction? conditions disappear those organisms disappear…
we come up to about one to three million years
before the end of the Cretaceous and we've got a
group that seems to be vulnerable to any kind of
extinction events that might be occurring at that
Global Warming Could Have Been
Contributed To by Organic Sources
Increasing concentrations of methane in the Earth's
atmosphere would force changes to the earth’ s
climate on a global scale. Aside from methane
coming from seismic sources, the suffocating gas
could also originate organically. This organic
methane would originate from increased numbers
of deep-sea algae deposits and from the digestive
processes of plant-eating dinosaurs. Increasing
water temperatures could have caused a
destructive feedback loop; Algae breeds better in
warmer temperatures , and the greater the
quantities of algae, the more methane, and
consequentially the warmer the environment would
Fossil evidence also suggests that Plankton
What was it? decreased in number during the Tertiary period.
This may help explain the destruction of many
The KT mass extinction event was a large-scale marine food webs which relied on them.
mass extinction of animal and plant species in a
relatively short period of time. There is a Adapting To The Change [Or Not..]
noticeable boundary indicated in the fossil record In the changing climate, animals better able to
[known as the KT boundary], which is marked by burrow, or semi aquatic in nature would have had
a mass extinction topping 17 families per million a higher chance of surviving.
years [around 15 families per million years above Harsh conditions would have had a damaging effect
the average]. It occurred roughly 65 million years on all life, however creatures whose food chains
ago. were based on detritus had a reasonable chance of
K is the derived from the German name Kreidezeit,
which translates as the Cretaceous Period. T is the
abbreviation for the Tertiary Period (an outdated
description for the period of time now covered by
the Paleogene and Neogene periods). The KT
boundary marks the transition between these two
Small mammals preying on dinosaur eggs have
been suggested as a contributor of the K-T
extinction. However it does not explain why so
many other species went extinct around, or the
iridium chemical anomalies in the K-T layer, and
could therefore be a contributor, not a cause to the
Repenomamus robustus was an opossum-sized
mammal about 1 m long and weighing around
14-15 kg living around 130 million years ago. A
Chinese fossil of it was discovered a few years ago
with the remains of a juvenile psittacosaur in its
stomach area. This is direct evidence that some
mammals fed on small vertebrates, including young
On this diagram the KT boundary [the last mass
extinction event] marks the termination of the
dinosaur, pterosaur and mosasaur genetic trees.
Food web disruptions – a threat to dinosaurs?
In the late Cretaceous, photosynthesizing
organisms, including phytoplankton and land
plants, formed the foundation of the food chain.
Evidence suggests herbivores declined when the
flora they depended on for food became scarce;
recently evolved flowering plants may have
outcompeted many of the non-flowering species Artist’ s impression of a Repenomamus – with its
that the dinosaurs relied on for food. . dinner.
Consequentially, predators higher up the food Source: http://my.opera.com/nielsol/blog/index.dml/tag/fossils
chain such as Tyrannosaurus rex also suffered as
prey numbers diminished. The origin of Birds
A number of groups of Neornithine birds [the
At the end of the Cretaceous there seem to have precursors to modern avian species] survived the
harsh conditions of the KT event as a result of
been no purely herbivorous or carnivorous animals.
their abilities to dive, swim, or seek shelter in
Many more species that were Omnivores, water and marshlands. Many species of birds can
insectivores and carrion-eaters survived the build burrows, or nest in tree holes or termite
extinction event, perhaps because of a more diverse nests, all of which provided shelter from the
diet which would act as insurance against declining environmental effects at the KT boundary.
food sources. Of the creatures that survived the
extinction, most fed on insects, worms, and snails.
This is significant as this food source fed on dead
With the decline of the dinosaurs, evolutionary
plant and animal matter. Scientists hypothesize
pressures changed. Long-term survival past the
that this detritus based food web fared better than
difficult conditions at the boundary was easier for
the plant based food chains as there would not the remaining species as they could now fill niches
have been a significant fall in the amount of left empty by the extinction of the dinosaurs. In
detritus [dead organic matter] available for the Darwinian sense, competition decreased for the
sustenance. surviving species, thus making it easier for them to
find food and the resources they needed to
It has been hypothesized that with levels of oxygen propagate.
falling, smaller animals, and animals with more
efficient respiratory systems [such as small Fossil Record Problems – The Signor Lipps
mammals – which may have required less oxygen
than much the larger dinosaurs] would have been
Although we have a lot of evidence for the
better able to adapt to these new conditions.
explanations put forward, we are using the fossil
record to date the period of the species’ existence. to ten billion Hiroshima bombs(Strahan 2004). The
The problem with this is that the fossil record is so result would have been an immediate loss of life
incomplete that most extinct species probably died from the impact event. The following ‘ nuclear
out long after the most recent fossil that has been winter’ would have caused an even greater loss of
found. However as the fossil record is the best way life as plants, unable to photosynthesize, died, and
of dating we have no other option. We also cannot the food webs on which they depended collapsed.
make any accurate estimations on how long a
species may have survived after the last fossil is
found. Scientists have also found very few
continuous beds of fossil-bearing rock which cover
an unbroken time range from several million years
before the K– T extinction to a few million years
after it. Unfortunately, this means there are a lot
of temporal gaps we have to fill in with guesswork,
due to our dependence on this record.
The KT Boundary – an impact event?
Artist’ s impression of the time immediately after
an impact event. A plume of vaporised water
punctures the atmosphere into space.
Where did it impact? - About Chicxulub
The KT boundary is the obvious on this rock –
marked by the claystone later in the middle - it
contains 1000 times more iridium than the upper
and lower layers.
Some believe that the KT mass extinction was
caused by a huge asteroid striking earth. It is rare
for an asteroid of a large enough size pass through
the earth’ s atmosphere intact, but when such
events happen, the results are cataclysmic.
Scientists believe an object 10 km wide slammed
into the earth on the tip of the Yucatan Peninsula,
in the Gulf of Mexico. It is thought that upon
striking, the comet would have sent a blanket of
dust and steam into the atmosphere; this emission
of dust and particles would have resulted in
environmental changes similar to a nuclear winter, Chicxulub [Nahuatl: “ The Tail of the Devil” ]
with this new artificial atmosphere of dust blocking Crater is an ancient impact crater buried
out radiation from the sun and causing a planet underneath the Yucatan peninsula, with its center
wide dimming and cooling. located approximately underneath the town of
Chicxulub, Yucatán, Mexico. It is thought to be
The impact blast have caused huge forest fires, the impact site of the impactor which is believed to
immense tsunamis in all directions radiating from have contributed to the KT extinction.
the crash site, severe storms due to meteorological
disruption, and eliminated all sunlight for a period
of 6 months under an ashen sky. The energy it
unleashed on impact would have been equivalent
A sample of Shocked Quartz found at Chixculub
Shattered or "brecciated" rock
Translated from Italian a breccia is “ a stone made
by cemented gravel” – which is exactly what they
are. Though there are a many varieties of
brecciated rock, such as types formed by geological
processes, breccias formed by an impact event are
quite distinct. They are layers of rock crushed
together by compressive weight, exerted by the
Topographical image of the Chicxulub crater, huge pressure of an impact event. This
showing local gravitational anomalies [note the compressive deformation is similar to the process
blue]. that creates shocked quartz.
In the winter of 2001/2 The Chicxulub Scientific
Evidence at Chicxulub Drilling Project (CSDP), Mexico, dug up an area of
There is a great deal of evidence that corroborates impact melt and breccias in the Yax-1 borehole 100
our theory that Chicxulub was formed by an m thick. (Kring et al. n.d.)
immensely destructive impact event. Evidence for
Chicxulub is also evidence for an impact event Further evidence comes from gravitational and
contributing to the extinction of the dinosaurs, as magnetic anomalies in the area. Gravitational
we know through detailed statistical modelling anomalies on the earth’ s surface suggest there are
[and the occasional thermonuclear test] that any variances the local magnetic field caused by
such impact would have disastrous consequences differences in the underlying mass of the earth.
for life. Such changes are deemed unnatural, as the
geological processes that created the earth
generally created a distribution of land uniform
Shocked quartz is formed when immense pressures enough to result in a gravitational field with very
little in the way of variety .One explanation for
cause a deformation of the internal structure of a
quartz crystal. Shoemaker discovered that it often these anomalies could come from the idea that
material has either been excavated or deposited by
formed in nuclear bomb testing sites. As impact
events release comparable amounts of energy, destructive intervention, such as an impact event.
finding shocked quartz in a crater strongly suggests
that it was not formed by volcanic activity, as Ejecta
pressures in a volcano are not high enough to cause Ejecta is the material released by an impact event.
the deformation. Ample shocked quartz has been As an impactor strikes the earth’ s surface, it
found at Chicxulub and the accompanying crash displaces a certain amount of material, which is
sites(Smit 2003), from this we can deduce that blasted out with great force and lands elsewhere,
Chicxulub is not a geological formation. often far from the impact site. Due to the extreme
conditions of an impact event, ejecta is often very
noticeable, even far from it’ s point of origin. Ejecta
from Chixulub have been located in the Cayo
District of central Belize, about 500 km southeast
of the Chicxulub impact crater. (Ocampo et al.
The collision of Comet Shoemaker-Levy 9 with
Jupiter in 1994 demonstrated that gravitational
interference can fragment an impactor, allowing for
multiple impacts over a period of a few days if the
comet should collide with a planet. This scenario
may have played out at the time of the KT Further proof – Stone In Peculiar Places
boundary. The Chicxulub impact [which impacted on water]
would have caused a Tsunami that must have
Other craters of around the same age as churned up billions of tonnes of sand from the
Chicxulub have been discovered, all between coast and dumped it on the ocean bed. This
latitudes 20°N and 70°N. They include the became the sandstone and when the sea level fell,
Silverpit crater in the United Kingdom, and the the rock was exposed.
Boltysh crater in Ukraine. They are much smaller
than Chicxulub but are believed to have been have The work of Hildebrand, a graduate student at the
been caused by objects many tens of metres across University of Arizona, found that such sandstone
striking the earth. This has led to the hypothesis deposits occur in many locations, but seem to be
that the Chicxulub impact may have been only one concentrated in the Caribbean basin.
of several impacts that happened all around the
time. A Final Clue
One of the largest pieces of evidence of
In 1997, palaeontologist Sankar Chatterjee drew environmental destruction from the KT period was
attention to a much larger 600 km (370 mi) Shiva a high concentration of fern spores. Ferns flourish
crater, located in the Indian Ocean. Due to it’ s whenever all other plants have been killed off by
monstrous size, it was tentatively suggested that some environmental devastation. The spores are to
this could have been an impactor in the KT be found well distributed on the geological KT
scenario. However, there is currently argument in boundary(Fleming & Nichols 1990).
the astrogeological field as to whether Shiva was
formed by an impact at all(Sankar). Alternative theories
There is the possibility of more concurrent
impacts, however any craters that might have The event could be linked to a combination of
formed in the Tethys Ocean would have been causes, as many of these are linked.
erased by tectonic events related to northward
drift of Africa and India. Environmental changes and the Deccan
More Proof – Rock Displacement, Shocked Quartz For about half a million years before the KT
And The Iridium Anomaly boundary, the world suffered a period of extremely
destructive vulcanism. Vast areas of the surface
where covered by molten lava. A million cubic
Iridium is a transition metal which is extremely
kilometres of material spewed out in what are
rare on the earth’ s surface but common in known as the Deccan Traps.
asteroids. Iridium is rare on the earth’ s surface as
it often forms chemical bonds with iron, which as a Information points to the 600 meters (2000 feet) of
heavy element, sinks to the earth’ s core. lava pouring out of them in as little as 30,000
years. This is enough to have possibly released a
Distributed through the material that makes up climate-altering amount of sulphur gases, and is
the KT layer there is an unusually high most probably a very significant contributor to the
concentration of Iridium. This strongly suggests climate change that is thought to have occurred.
that an object with a high concentration of iridium (Geological Society Of America 2005)
impacted the earth with enough force to disperse
the materials of which it was made all over the
Additional evidence suggests that most of the
surface of the planet. This same iridium rich dust
Deccan Traps flood basalts were erupted in a <1
could have been responsible for the nuclear winter
Million year interval which coincided with the K/T
that blanketed the atmosphere and was so deadly
boundary. The global environmental effects from
to life. This layer is also very rich in soot.
this volcanism could be similar to a large impact,
such as global dimming due to particle release into
“ … it contains enough soot to correspond to
the atmosphere. However, the timescale of the two
burning down all of the forests of the world. This
processes would be different. The full consequences
suggests that massive fires were touched off at the
of an impact event may only take a few months to
time of impact” (Hartmann n.d.).
manifest, whereas the effects from volcanism would
be spread over at least a few hundred thousand
This soot evidence suggests forest fires of an years. Therefore resolving these hypotheses
unparalleled scale. Such a quantity of huge fires requires estimating the duration of the K/T event.
could have caused a large conversion of oxygen to Unfortunately most chronological techniques do
carbon dioxide, and thrown up even more detritus not have sufficient resolution to date geologically
into the sky. This would have the effect of making ‘ instantaneous’ events
environmental conditions even more inhospitable.
Air would harder to breathe, and declining light The Deccan Traps could have caused extinction
would result in falling temperatures and available through several mechanisms, including the release
light for plant photosynthesis. of dust and sulfuric aerosols into the air which
might have blocked sunlight and thereby reduced
photosynthesis in plants. In addition, Deccan Trap struck at the time of the KT boundary. There is
volcanism might have resulted in carbon dioxide also no doubt that this impactor was powerful
emissions which would have increased the enough to severely disrupt the ecology of the earth.
greenhouse effect when the dust and aerosols What is called into question is the idea that this
cleared from the atmosphere. impact could be the sole cause of the extinction of
so many species. Evidence suggests that other
causes could have played their part. A gradually
worsening environment caused by increased seismic
activity in regions such as the Deccan Traps.
Darwinian pressures, due to disruption introduced
by innovative newly evolved species, such as small,
devious mammals. Lastly, additional speculation
coming from astronomical explanations such as
variations in the earth’ s orbit and gamma ray
bursts could also bear some scientific weight, given
time and a little more proof. Perhaps Chicxulub
was the finishing blow to a dying species?
Jan Smit, Professor of Event Stratigraphy at the
The Deccan Traps – notice the ridged surface,
University of Amsterdam and an acknowledged
which geologists believe was caused by the layered
expert on sedimentology, writes on his personal
accumulation of thousands of years worth of lava.
Source: http://farm4.static.flickr.com/3185/2575165118_c8c6c29282_o.jpg website;
Disease SMIT: “ there is evidence for a decline of some of
Another, possibly far flung explanation has been the biotic groups becoming extinct at or near the
linked to falling sea levels. As sea levels fell, more KT boundary, but decline is on different
and more land bridges started to appear on the timescales, and attributable to various non-impact
earth. The dinosaurs would have been able to cross related causes (cooling, Deccan traps). There is
these bridges into new territory, bringing their little doubt however, that the mass- and final
microbes with them. Millions of years of careful extinctions all occur very close to and at the KT
evolution would mean that the migrating dinosaurs boundary, suggesting a cause and effect
where immune to these bacteria, whereas dinosaurs relationship with the Chicxulub impact. These
native to the regions they were colonizing were effects, despite almost two decades of research, are
not. This could have resulted in a kind of still poorly understood” (Smit n.d.).
unintentional biological warfare, in which the
species native to the regions where assailed by ARCHIBALD: “ Six million years prior to the KT
bacteria which they had not time to evolve boundary there were about twenty species of
immunity against, similarly, dinosaurs migrating to ammonites in the world's oceans. Three million
these new regions would also be entering a years before the KT boundary there were only
territory full of microscopic enemies unknown to fifteen or so and one million years prior to the KT
their immune systems . Although perhaps far boundary we have less than half of what we
flung, this bacterial invasion has actually been seen started out with, we have less than ten species so
documented in humans. Around the time that the extinction event has already been going on for
Europeans first visited the new world it has been millions of years. We see the same pattern in the
estimated that European disease wiped out 95 fish record, in the terrestrial reptile record, even in
percent of America's pre-Columbian the mammal record. All of these groups were
population(Diamond 1999) undergoing an extinction event for millions of
years and it would be absolutely amazing to me if
Orbital Variation dinosaurs weren't undergoing.. the same sort of
Changes in the Earth's orbit that could have been long term extinction… Clearly dinosaurs were
responsible for climactic variations which incredibly unlucky at the end of the
contributed to a more hostile environment. In this
Cretaceous to have all three things happen at
scenario, the dinosaurs couldn't adapt to the cold,
the same time.”
but the furry mammals could. This theory is
consistent with the climate in the late Cretaceous;
So we have established that the KT boundary is
toward the end of this period, there was a drop in
not a single point in time, and is instead a period
sea level, causing land exposure on all continents,.
with a length not yet agreed upon by scientific
From the upset of the global thermodynamic
consensus. We must make a distinction between
system came more variance in seasonal conditions,
the KT impact event and the KT extinction, as
and greater extremes between equatorial and polar
evidence suggests they are not mutually exclusive.
temperatures. As of yet proof is not abundant for
The KT impact event is clearly a contributor to
this theory and it would be exceptionally hard to
the KT extinction, but cannot be deemed the sole
test this hypothesis using the fossil record.
cause. Lastly, as our evidence from this time is
sparse and relies on the fossil record, which is
Conclusion – The Experts Speak incomplete at best, we cannot draw any certain
It seems there is ample proof that an asteroid conclusions. We can only offer more hypotheses
and hope that in the coming years, additional
improvements to the fossil record will give us a
better picture of what was happening at the time.
– Jack Oughton
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