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Re: [escepticos] RE: Dinosaurios de moda
He encontrado que Disney no es el único científico que rechaza
la teoría del aerolito como causante de la masiva desaparición
de dinosaurios.
He encontrado, apenas empecé a buscar, cerca de cincuenta
sitios en Internet que exponen teorias contrarias a la desaparición
de los dinosaurios por culpa de los aerolitos.
Asteroids of Death by E.S. Matalka discusses the asteroid impact
hypothesis for the
extinction of the dinosaurs. Matalka is critical of this idea. He
suggests David
Archibald's marine regression hypothesis is more likely.
Carriers of Extinction by Carl Zimmer suggests that the megafaunal
extinctions at the
end of the last ice age were caused by pathogens carried by migrating
humans.
Chicxulub Impact Crater Provides Clues to Earth's History by Virgil L.
Sharpton dicusses
the most likely site for the main impact at the end of the Cretaceous,
Chicxulub in the
Yucatan, Mexico.
Chicxulub Seismic Experiment discusses an ongoing project by the Crustal
Geophysics
group at Imperial College, London, U.K. to study the Chicxulub impact
structure. In the
summer of 1996 the group acquired a series of wide-angle and
normal-incidence reflection
seismic profiles onshore and offshore across the structure.
Cracking The Mystery by Anthony Spaeth discusses the suggestion by
Sankar Chatterjee
and Dhiraj Kumar Rudra that a 600 km crater, mostly submerged in the
Arabian Sea off
Bombay, India, is the site of the "dinosaur killer" impact at the end of
the Cretaceous.
Chaterjee and Rudra suggest that this "Shiva crater" and that one at
Chixculub were
caused by fragments of the same large object striking about 12 hours
apart as the Earth
rotated.
Crashing Comets and Dead Dinosaurs offers an overview of the impact
theory for the
dinosaur extinction at the end of the Cretaceous. There's also an
interesting description
by Dennis Schatz of how to make your own comet for classroom
demonstrations.
Crater of Death provides the transcript of a BBC television program
about the Chicxulub
crater and the end-Cretaceous extinction event.
Dinosaur Extinction: One More Hypothesis offers the text of the 1956
paper by M. W.
De Laubenfels from the Journal of Paleontology suggesting a large impact
might have
caused the end-Cretaceous dinosaur extinction.
Dinosaur Extinction Page by A. Buckley discusses the asteroid impact and
volcano theories
for the demise of the dinosaurs.
Dinosaur Volcano Greenhouse Extinction by Dewey McLean discusses the
volcano versus
asteroid extinction theories. McLean is the originator of the volcano
theory, which couples
the K-T extinctions to a major perturbation of earth's carbon cycle
caused by the Deccan
Traps mantle plume vulcanism.
Dinosaurs, Comets, and Asteroids --Resources from NASA offers an
excellent list of web
sites, books, article, teacher's resources about impact-induced
extinctions.
Dinosaurs -- Fact Sheet discusses why they went extinct.
Disaster from space discusses evidence in favor of a large impact event
causing the
extinction at the end of the Cretaceous.
Do or Die: Extinction from the St. Louis Science Center summarizes
several ideas about
why the dinosaurs became extinct at the end of the Cretaceous.
Dusk Of The Dinosaurs by Michael J. Benton reviews two books about the
dinosaur
extinction controversy: T.Rex and the Crater of Doom by Walter Alvarez
and The
Great Dinosaur Extinction Controversy by Charles Officer and Jake Page.
End of a Legacy: How did the dinosaurs meet their demise? by Andrew Maas
is an eigth
grade science project surveying some of the possible causes for the
extinction of the
dinosaurs.
Extinction pages lists Web pages which discuss extinctions.
Extinctions due to impacts, past and future offers the abstract and
audio (RealAudio
format) of a presentation by Owen Toon.
Extinctions: Cycles of Life and Death Through Time from the Hooper
Virtual
Paleontological Museum discusses the asteroid impact and volcano
hypotheses for the
end-Cretaceous extinction. Includes sections on mass extinctions in
Earth history, minor
extinctions, patterns of extinction, extinction in the early Holocene,
and more.
Georges Cuvier (1769-1832) was one of the founders of vertebrate
paleotology. Cuvier
established extinction as a fact. He ascribed extinctions to periodic
"revolutions" or
catastrophes, events which Cuvier cosidered to have natural causes.
Impact Catastrophe that ended the Mesozoic describes a Hypercard stack
for the
Macintosh which discusses the impact catastrophe at the end of the
Cretaceous.
K-T Event discusses the impact event at the end of the Cretaceous.
Mass Extinctions deals with the dinosaur extinction as well as mass
extinctions in general.
Possible Collisions on Earth due to Asteroids and Comets by Karen
Krupinsky and Tammy
Seergae offers a student activity to research and evaluate different
theories for the
extinction of the dinosaurs, including the impact hypothesis.
Scientists find evidence of dinosaur-killing asteroid - Feb. 16, 1997
offers the text of an
AP wire story detailing new evidence supporting the impact hypothesis
for the extinction
of the dinosaurs. Core samples in the Caribbean indicate a "dead zone"
lasting about
5,000 years after the impact.
Sky is Falling! or What Did in Dino? discusses the end-Cretaceous impact
extinction
hypothesis.
T-Rex and the Death Star from the H. V. McKay Planetarium in Melbourne,
Australia
discusses the impact theory for the extinction of the dinosaurs.
What killed the dinosaurs? surveys a number of different hypotheses
advanced to explain
the extinction of the dinosaurs.
Brian Goff's What killed the dinosaurs? is critical of the impact theory
for the demise of
the dinosaurs.
What Really Killed the Dinosaurs? from New Scientist, August 16, 1997
discusses the
asteroid impact, volcano, giant molecular cloud, and giant
disintegrating comet hypotheses.
When the sky fell on our heads: Identification and interpretation of
impact products in
the sedimentary record by Philippe Claeys assesses the geological
evidence for a killer
strike in terms of impact products at the end of the Cretaceous.
Works in Progress: Extinction reports on recent research into a simple
model of
extinction proposed by Mark Newman and Gunther Eble. They suggest all
extinction is
caused by environmental stresses, such as the impact that killed the
dinosaurs.
De todos esos sitios me ha parecido muy destacado el de
la Univ. de Berkeley que les paso (copio algo nomás, es muy largo).
A la extinción por causa de un aerolito le llama "la hipótesis
de Álvarez", quien la formuló en 1980 y se basaba en la
existencia de esa capa de iridio que dió lugar a burlas en
esta corrala porque creyeron que era un invento mío.
La discusión está planteada entre los que son partidarios de
a) causas intrínsecas y graduales
b) cusa extrínseca (el aerolito del Yucatán)
Quiere decir que habiendo dos bandos, no es tan terrible
que yo haya optado por uno de ellos.
Además se puede ver que la teoría catastrofista extrínseca
está en franca retirada.
Notablemente los partidarios de las causas intrínsecas y graduales
explican la capa de iridio por masivas erupciones volcánicas
que ocurrieron en la India hace 65 millones de años, entre
el cretáceo y el triásico. Parece ser que las erupciones son
ricas en iridio (metal raro parecido al platino)
http://www.ucmp.berkeley.edu/diapsids/extinctheory.html
He aquí las conclusiones:
There has been no settlement to the issue so far, and no clear one is foreseeable.
Both sides claim to hold the majority of
proponents in science; it seems that (greatly over- generalizing) many
paleontologists lean towards the intrinsic side, while many
astronomers and physicists favor the extrinsic side, and geologists are probably
evenly split between the two.
All of the evidence cited for the extrinsic catastrophist side is claimed as
evidence by the intrinsic gradualists for their side or
against the opposite side- volcanoes could create the iridium layer, shocked
quartz, soot, and impact ejecta; the makeup of the
iridium layer is not uniform in all areas, so it could be meaningless; and so on.
The main problem with both hypotheses is the issue of the selectivity of the mass
extinction; as you saw before in the
background section, some organisms were wiped out, while others were unaffected.
Can climate change really explain the
differential selectivity of the K-T event? Our lack of understanding of the
physiology of dinosaurs makes the issue more
complex; if they were endothermic, why did they not survive like birds and
mammals? If they were ectothermic, why did small
dinosaurs not survive like small reptiles?
Also, many studies have focused on the extinction of dinosaurs alone, and have
forgotten about the more substantial marine
ecosystem collapse. The fossil record suggests that some marine reptiles died out
several million years prior to the K-T
boundary.
Other major problems with the issue are that it is not easy to prove (test)
causation (as noted before), and that most of the ages
of the rocks that different evidence comes from are questionable. It is not
certain whether there is a gradual decline in the global
fossil record, or if there was a sudden catastrophe; some studies in some areas
show evidence pointing to different answers.
Ultimately, we just don't know yet for sure. The two main schools of thought are
split fairly evenly among scientists familiar with
them. Either an intrinsic or extrinsic cause for the extinction would have complex
biotic effects on ecosystems which would look
confusing in the fossil record. There could well have been different, even
separate extinctions in the oceans and on land; the
marine fossil record does support a slightly rapid decline, while the terrestrial
record (especially in North America) strongly
suggests a more gradual decline (but again, has a fragmentary fossil record). If
an extraterrestrial impact occurred during a
gradual decline, that might explain the seemingly contradictory evidence. If you
are looking for an opinion here from a
paleontologist's point of view, it seems that the simplest explanation is that the
climatic changes induced by the shifting continents
and the regression of the continental seaways were the ultimate cause (at least in
North America), but this has not been (and
may not ever be) proven. There is much work to be done, and much value to this
work -- understanding the K-T extinction
would help us to understand mass extinctions in general, and might provide a
glimpse into the fleeting, evanescent nature of our
own mortality.