Dinosaur Extinction

Discussion in 'Biology & Genetics' started by Neutrino_Albatross, Jan 23, 2003.

  1. Neutrino_Albatross Legion of Dynamic Discord Registered Senior Member

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    While doing a little reasearch for a rather idiotic religion thread i came across a website saying that the theory that dinosaurs were wiped out by an astroid impact is not widely accepted before. Ive never heard anything like this before but I think its fairly convincing and Id like to see what other people think: http://www.livingcosmos.com/k-t.htm
     
  2. Jaxom Tau Zero Registered Senior Member

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    Okay, first thing, it's promoting a book. This doesn't invalidate the ideas, but it's usually a warning. That said, I'll list the things I'm skeptical about. Doesn't mean they're wrong, simply means they send up red flags to be investigated more.

    1) "The impact was supposed to be the site of Chicxulub, Yucatan, and now a multi-ringed crater is noted in the North Sea of approximately the same age. Yet, the Southern Hemisphere was just as devastated as the Northern Hemisphere."
    The impact possibly could have set off the Deccan Traps in India, then I believe south of the equator and opposite the impact site. That, plus I don't believe the equator is as good a protector as once believed from global atmospheric disasters.

    2) "The site of the proposed impact at Chicxulub, Yucatan, as part of the Caribbean Plate, was undergoing uplift, and plate rotation from the Pacific to the Atlantic during the Cretaceous, which is extremely difficult to reconcile with an impact."
    Not sure why this would matter.

    3) "Recent well coring at the Chicxulub (e.g., well log No.6) indicates that the structure may be volcanic or a cryptoexplosive geobleme (a structure caused by an explosion ejection from the Earth)."
    Fair enough, but was that only one site? Hell of an ejection if that's true, but recent discoveries about places such as the Yosemite area would make me accept a buildup and eruption possible. However there's a lot of evidence to point to impact.

    4)"Iridium is found almost globally and is found in strata that is not the same date everywhere, when it should be found mostly in the Yucatan region and bare the same date. The greatest abundance of iridium was found on the Hess Rise in the mid-Pacific, some 10,000 kilometers (6,200 miles) away from Chicxulub. In Raton Basin, New Mexico, the iridium was deposited during normal polarity of the geomagnetic field, not the reversed polarity of other sites. Many irregularities in iridium occur worldwide (by orders of magnitude)."
    Last I read the iridium ages were very close in all areas found. It was the original smoking gun or extraterrestial origin of a global scale, and pointed to that single age. Maybe something new...?

    5) "Some evidence indicates that the shocked quartz did not originate by impact, but may be volcanic or tectonic in origin."
    Mentioned elsewhere about the Deccan
    Traps, the site says that volcanic shocked quartz would be larger in size that impact, and be localized. However, the shocked quarz found accompanying the iridium layer globally is consistant with impact sizes.

    6) "Some areas, such as at Gubbio, Italy, display a long interval of shocked minerals which is bisected by the boundary. Also at Gubbio, there are five iridium peaks, indicating the need for five impacts, and therefore, five craters with no other impact structure of the right age (with the possible exception of Manson Crater in Iowa). Similar extended zones can be found in the Pacific, Atlantic, Denmark, Spain, France, Germany and New Zealand."
    Multiple impacts maybe. And craters are hard to find, look how long it took to find Yucatan's, as big as it is.

    7)" In most situations the iridium and other noble metals are associated with organic compounds (kerogen and organic carbon or coal) from dead biomass, which is likely to be the source of the metals."
    I thought iridium was rare on earth, period.

    8) "The abundances of noble metals is more consistent with earthly compositions than extraterrestrial sources at many sites. Also other metals typical of meteoritic materials are missing in some sites with iridium or the ratios are not typical of impact debris. Moreover, the shocked quartz at some sites is more consistent with water transport (ocean erosion) rather than atmospheric (as would occur with impact)."
    Not all meteors are the same. We're not experts on meteor consistance anyway, that's wht the NEAR mission was so important. And the impact was in water, with the resulting surge out and back into the crater. Could this account for what's found?

    9) "Other times of impact did not cause such extensive mass extinctions."
    Actually I think there's correlation in a few cases, the few big impacts we know of. The rest could be other factors, or lost evidence. 65 million years is relatively recent, and look how much debate it's causing.

    10) "An impact is theoretically less likely to initiate widespread tectonic activity, and sea level rise, which occurred at the end of the Cretaceous."
    Lot of energy, directed through the earth. Who's to say what will happen? How much experience do we have with impacts? Look at what happened on Jupiter, and that was a small comet, not solid. Actually, a solid might not have made as much of an explosion, but anyway...

    11) "The climatic shift should have went from a drastic drop in temperature (with sunlight blocked) to progressively hot temperatures (the Greenhouse Effect). "

    Not sure on this one myself.

    12) "The mass extinctions of the time do not fit the impact theory: (a) The extinctions were not instantaneous and were selective. (b) Many species were in decline before the time of the proposed impact. (c) If the Yucatan region were the impact site then the greatest mass extinctions should be in southeastern North America, Central America, and northeastern South America, but were not (it seems that the greatest dinosaur fossil graveyard is in the Gobi Desert, on the other side of the Earth, and most extinctions were along mid-latitudes, not the tropics). (d) The huge dust and water vapor cloud should have caused plant extinctions the most, but it did not, and equatorial species should have been hit the worst, but it was mid-latitude species that were affected the most, and most mass extinctions were animals. (e) Photosynthetic nannoplankton survived into the Tertiary, and Cretaceous and Tertiary species even coexist in land-based marine sections of the Tertiary. (f) Tropical insects should have become extinct, but persist into the Tertiary. (g) The dinosaurs appear to have undergone gradual extinction in at least some locations."
    Some good question here, I'd have to research more to argue them. One thing, "The extinctions were not instantaneous and were selective", one of the arguments for the theory this site pushs is why some fossils have been found in the opposite, suddenly killed, in mid battle for one. It's arguing both sides it seems. Wouldn't a shockwave moving at the speed of sound, plus the sudden heat blast, instantly kill those exposed?

    13) "High-energy terrestrial explosions, called geoblemes or cryptoexplosions, have not been studied, nor have laboratory simulations been tested. Therefore, much of the evidence for impact is somewhat biased by not considering the evidence in light of all the possibilities. For example, a number of journal articles have shown that the craters on Mars and other planets are dynamically related to the core, and therefore, are internal in origin. Also, the structural similarities of multi-ringed craters with a central peak are too uniform, regardless of size and proposed angle of impact, for them to be impact craters; laboratory experiments show different structures for different angles and impactor size. This suggests that multi-ringed craters with a central peak, like that of the Chicxulub, are internally produced."

    There are craters such as this on the Moon, which is dead. I thought the argument of craters being volcanic had been done away with years ago.

    That's enough (probably too much) for now. What evidence of radiation deaths is there among dinosaurs anyway? That seems to be the biggest argument going for this theory, but how do you preserve evidence of this?
     
  3. valich Registered Senior Member

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    The meteor hit off the coast of the Yucatan Peninsula in Mexico and spread out a layer of ash that covered the entire earth's atmosphere, blocking out the sun's photons and ultraviolet rays. This caused the extinction of the dinosaurs except for birds (Aves) and Crocodylians that still survive today.
     
  4. I gather you mean "was not widely accepted before"?

    Perfectly true, in fact the chap who originally proposed the idea was thought fanciful in the extreme by the the establishment at the time... Funny how times change, eh? ;)

    Most, pre-impact theories, attributed the mass extinction of 65 million years ago as being down to the cumulative effects of the basalt larva planes that had been pouring forth for millions of years leading up to the event - the cumulative effects of all that sulphur dioxide pouring unchecked into the atmosphere changed both climate and atmospheric composition.

    This was an ongoing catastrophic event which had been going on for a very long time with cumulative effect.

    These days the Impact, though widely accepted as being part of the larger picture, is thought of more as being probably the last nail in the coffin of the Dinosaurs, more than the actual coupe de gras...

    Possibly, if the meteor hadn't have happened life for them may have continued for another few million years yet - but basically the world was becoming an increasingly hostile place for all forms of life - Dinosaur species were becoming extinct throughout this period purely through this already ongoing mass extinction level event provided by dear old mother Earth leading up to the ELE meteor impact so, the establishment still ended up getting their own way with the argument.
     
  5. valich Registered Senior Member

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    3,501
    About the same time dinosaurs became extinct, mammals elvolved out of the same phylogentic clade called Amniota that dinosaurs (Archasauria, originally Diapsida) evolved from. The animals left on earth were then mammals and other Reptilia (turtles, lizards, crocodiles, birds and other reptiles, and of course aquatic life and arthropods (insects, spiders). Do we know what mammals made their way through this massive extinction, i.e., in what form or species they were at that period of time, that led to homo sapiens?
     
  6. alibim Registered Member

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    Mammals evolved well before the dinosaurs became extinct, although while the dinosaurs were the dominant vertebrates, mammals were probably small & nocturnal. Incidentally, mammals are synapsids while dinosaurs & birds are diapsids - the names refer to the number of openings in the bones overlying the cranium.
     
  7. valich Registered Senior Member

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    3,501
    I did read that the mammals back then were small, like rodents, but I don't think that in relative terms that mammals evolved way before dinosaurs. Also there seems to be a confusion as to whether mammals evolved directly from reptiles, but current phylogeny shows that they evolved from the same "ancestor" of reptilia. But I wonder if both of these could be mistaken and that mammals developed from a totally different lineage after fish came on shore and developed into tetrapods.
     
  8. kazbadan Registered Senior Member

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    1) Why only the dinossaurs died, but not mammals? Is there any relation with the fact that mammals are "hot blood" (i dont know how do you say this in english) animals?

    2) Which i sthe most acceptable theory, actually, about the extinction of dinossaurs? Still be the same about the meteor?
     
  9. fadingCaptain are you a robot? Valued Senior Member

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    1,762
    I have some questions I havent been able to find answers for:

    How long did it take for dinosaurs to die out? How long was the atmosphere blocked out from the impact debris cloud? What kinds of birds were around at that time?
     
  10. valich Registered Senior Member

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    3,501
    Hot blooded animals are called endotherms because they are dependent on the heat production generated from their own bodies.

    Cold blooded animals, like reptiles and amphibians, are called ectotherms because their body temperature is dependent on the heat of the environment.

    This is an excellent point. Since dinosaurs are thought to have all been cold blooded, evolving from reptiles, they would have been the most likely to die out because when the earth was covered over by the debri and particles from the meteor blast, this blocked out the sun light and caused the earth's atmosphere to become cold. Small mammals and aquatic life would have had a better chance of survival since they could still generate their own heat. Many of these small mammals were probably burrowing rodents, so they could also keep warm by living in underground nests.
     
  11. valich Registered Senior Member

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    3,501
    I'm not sure if we'll ever know the exact answer to these questions, although I'm sure some scientists could estimate it. How long it took for the extinctions to take place would depend on the amount of atmospheric cover blocking out the sun's rays, which life died out first, loss of their food source (plants had no sunlight for photosynthesis and would have died out, thus no food for herbivores), and the animals location.

    We do know that the thickness of the layer of ash left over from the meteor impact off the coast of the Yucatan Peninsula decreases from the distance of its impact. The impact also generated massive tidal waves - nothing comparable to what you see today - that would have completely and almost instantaneously wiped out any land-dwelling terrestrial life within a few hundred miles of the impact area. Then came the covering of the upper layer of the earth's atmosphere with the ashes that blocked out the sunlight. Winds would've carried it around the world, probably for weeks, months - hard to say how long. And even harder to say how long this would have affected the lowering of the earth's temperature.
     
  12. valich Registered Senior Member

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    3,501
    This may be surprising to some of you but you should also know that within the 4.5 billion year history of the earth, we have undergone "five" mass extinctions, but because the meteor 65 million years ago was the most recent, this is the one we all talk about!

    Since life evolved on earth 3.86 billion years ago, about 99.9% of the total animal species that have ever existed on earth are now extinct. And for most of those species, we have no idea what they were or what they looked like because there are no fossils to show them. Think about what we imagine as extraterrestrial. Fossils usually only form when there is cartilage or hardened bone-like material to preserve them, and only under the right conditions to preserve it. Most of the animals in early life forms had no hard material substances to even be preserved. It is estimated that if every person in North America were to be wiped out by some natural force, only three fossils of all these people would remain to "somehow" be found.

    1) 65 million years ago: 76% of species disappeared from the meteor impact off the coast of the Yucatan Peninsula in Mexico.

    2) about 206 million years ago: a large meteor crashed into Quebec, Canada wiping out 65% of the species on earth at the end of Triassic period.

    3) about 250 million years ago: a large meteor crashed into Northwestern Australia, with a massive outflow of lava and the extinction of about 96% of the world's animal species.

    4) 355 million years ago: two large meteorites hit Nevada and Western Australia possibly causing the extinction of 75% of the world's species. Scientists are still uncertain about the exact cause.

    5) about 443 million years ago: massive glaciers formed causing sea levels to drop 50 meters and ocean temperatures to drop resulting in the extinction of 75% of all animal species.

    Therefore only about one tenth of one percent of all animal forms that ever existed on earth still exist today in one form or another (0.1%).
     
  13. Ophiolite Valued Senior Member

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    8,312
    Valich, you are being somewhat disingenuous by suggesting that the meteorites as the cause for three of the four mass extinctions before the KT event [even considering the caveat of 'possibly' in one case.] We do know there were extinctions. The causes are nowhere near as well established as the KT event, and frankly, as you yourself have noted this may have only been the final nail in the coffin.
    The truth is one of the more interesting problems facing geologists at present is the cause and the character of these earlier mass extincitions. You might like to add a sixth, namely the one we are undergoing at present. And a seventh when the oxygen being pumped into the atmosphere by cyano-bacteria two or three billion years ago wiped out most of the earlier species. Or the decimation that must have accompanied each Snowball Earth episode.
     
  14. valich Registered Senior Member

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    Well I guess I should take that as a compliment as I certainly never claimed to be anything close to a genius, but I don't follow your point about "the final nail in the coffin" bit.

    Each time there was an extinction, the diversity of species on earth rebounds - sometimes at a tremendously rapid rate. We know of these other extinctions because of the layers of ash that have been found within the layers of shifted or collapsed geological formations, like what happens in earthquakes. Or by reading these layers through the wearing down of the side of a cliff by a natural cause, like how the Colorado River formed the tall cliffs that make up the Grand Canyon. And we know that the species became extinct and then other species rebounded at a given rate through fossils and through carbon isotope dating. We can determine temperature and oxygen levels at different times in history because of the molecular makeup and oxygen concentration that we know of from the deep soil deposits we have drilled out and the ice layer contents that are being drilled in Russia and in the Arctic.

    I certainly do agree with you that mankind is now providing the earth with another extinction - possibly even the worst one ever! And yes, when cyanobacteria liberated the way for aerobic life to evolve and florish on the earth by their production of O2, then there had to be a corresponding decline in the previous anaerobic life on earth. But because these unicellular prokaryotes lacked any cartilage or bones (endoskeleton or exoskeloton - hard outer layer, like a shell), they left no fossil traces.
     
  15. Ophiolite Valued Senior Member

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    8,312
    My apologies. I thought you had written that the Chicxulub impact may have been the final nail in the coffin for the dinosaurs, which I could agree with. I am not yet wholly convinced that this alone can account for their demise.
    I am certainly very far from convinced that any of the earlier extinction events are related to impacts. You are being rather optimistic in suggesting that we have solid evidence to support these events. I don't even buy (yet) the alleged Permo-Trias impact evidence.
    You note that the prokaryotes left no fossil traces. One might add apart from the massive numbers of stromatolites found, I think, on every continent throughout much of the Pre-Cambrian.
     
  16. valich Registered Senior Member

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    And stromalites are very beautiful structures at that: proof of the evolution of cyanobacteria. Some stromalites are living stromalites while others are fossils, so you're right, in some case they leave strange fossil evidence. Had cyanobacteria not be alive today though, how would we know what these fossilized striated forms are? Perhaps only geological anomalies.

    I am not a scientist so I have not participated in any excavations or research on the previous extinctions but this is what is being written down in many textbooks as fact and I haven't heard of any researchers going out there trying to disprove them. Although I did take a geology course and our professor did point out to us the most recent ash layer (65 mya) and evidence of where the glaciers stopped and then receded in North American after the last ice age. You could see a clear line of large boulders extending throughout fields on-and-off over a fifty mile distance that abrubtly ended when they began to recede.
     
  17. Ophiolite Valued Senior Member

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    What has this to do with the price of bread? You stated that prokaryotes left no fossils. I corrected you. Your enthusiam for the field of Earth Science is very clear and I applaud it. You will understand, I think, that it is helpful to others reading these threads if the facts, as far as possible are indeed facts. I have noticed a couple of occasions where your enthusiasm seems to have outstripped your research. I hope you will not take it amiss if on those occasions I seek to correct you. Naturally you are free to return the favour.

    Please cite a single textbook in which the mass extinctions,other than the KT boundary event, you list in yesterday's post are attributed exclusively or primarily to bolide impact.
     
  18. valich Registered Senior Member

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    You really do have sharp mood swings that are counterproductive to rational scientific enquiry and learning.

    I mentioned that anaerobic prokarytes left no fossil traces - though I may be wrong. If so, please correct me. The cyanobacteria that form stromatolites are considered aerobic bacteria.

    You're other question about the previous mass extinctions:

    "Five major mass extinctions have been identified, the most severe of which occurred at the end of the Permian Period, approximately 250 million years ago, at which time more than half of all families and as many as 96% of all species may have perished. The most famous, and well studied extinction, though not as dramatic, occurred at the end of the Cretaceous Period (65 million years ago), at which time the dinosaurs and a variety of other organisms went extinct. Recent studies have provided support for the hypothesis that this extinction event triggered by a large ateroid which slammed into the earth, perhaps causing global forest fires and obscuring the sun for months by throwing particles into the air. This mass extinction did have one positive effect, though; with the disappearance of dinosaurs, mammals, which previously had been small and inconspicuous, quickly experienced a vast evolutionary radiation, which ultimately produced a wide variety of organisms, including elephants, tigers, whales, and humans."

    from "Biology," by Raven, Peter H. and George B. Johnson, 6th edition
    (International Edition), 2002, page 473.

    William K. Purves, et. al.'s book "Life: The Science of Biology," 7th edition, 2006 also has a nice chart summarizing these five extinctions on pages 444-445 along with charts that show the sea level, oxygen concentrations, earth's temperatures and glacier periods throughout history from the PreCambrian Period right up until the present. These charts are useful in comparing these mass extinctions with other environment changes that occurred at the same time.
     
  19. invert_nexus Ze do caixao Valued Senior Member

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    9,686
    Valich,

    I don't think so. I think he's just realized that you seem to copy and paste a lot of stuff into your posts that aren't always relevant (and are often shown to be incorrect or misinterpreted.) I've gathered a viewpoint of you as someone who wants to appear to be really knowledgeable, but is, in fact, googling for a lot of it.

    This forum isn't about showing off copy and pastes or our google skills. It's about open and honest discussion. (Hey. At least you're not ressurecting dead threads like you were. Your name is still stretched out thee pages long though...)

    Anyway.

    You'll notice that this paragraph you quoted refers to the KT event. The KT event is the only which has been proven to be caused by a meteoric impact. The other extinction events don't have the same evidence. There are conjectured theories that perhaps certain impact craters were from the same general time period and that perhaps they had a part to play in them, but only the KT event has the world-wide layer of iridium (I think it's world-wide. I'm sure that Ophiolite would know the answer to that. This is his area of expertise, after all.)

    The others are theoretical without this evidence. Highly theoretical. And if your textbooks are teaching them as more than theoretical then your textbooks are wrong. I think that the fault might be either in your own misinterpretation of what the textbooks are teaching (that meteoric impacts might have played a role but that the case is not closed) or that your teachers have. I've known several teachers in my time that have vastly misrepresented their curriculum due to their own ignorance. Some even outright confabulated (baldfaced lies.)


    quelquechosedautre,

    Shutup.
    Aren't you the douchebag who was posting garbage about who really built the pyramids or some other pseudo crap a while back? If so, go away.
     
  20. valich Registered Senior Member

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    3,501
    "The fossil record also shows that, of all organisms that have ever lived, only 1% survive today. All others are extinct."

    from "Ch. 10 Evidence of Evolution."
    http://www.whps.org/schools/hall/departments/science/Biology/Documents/Chapter 28.doc

    "Stromatolites have been described from various units in the Archaean but their cyanobacterial origin is hard to prove and even their biogenic origin is often controversial - many could also have been formed abiogenically by rapid marine precipitation of aragonite or by hydrothermal precipitation of barite and chalecdonic quartz."

    from "HOW OLD IS AEROBIC PHOTOSYNTHESIS? A FRESH LOOK AT THE FOSSIL EVIDENCE," by BRASIER, Martin D., 2001.
    http://gsa.confex.com/gsa/2001ESP/finalprogram/abstract_7831.htm

    "The oldest known structured fossils are most likely stromatolites. Believed to be formed by the entrapment of minerals by mucous-like sheets of cyanobacteria, the oldest of these formations dates from 3.5 billion years ago. Fossilized deposits of heavy carbon (acritarchs) that are also indicative of earlier life (3.8 billion years ago) are currently proposed as the remains of the earliest life on Earth."

    from "Fossil", in Wikipedia
    http://en.wikipedia.org/wiki/Fossil

    "Scientists have fossil evidence of bacterial life on Earth ~3.8 billion years ago. At this time, the atmosphere of the Earth did not contain oxygen, and all life (bacterial cells) was anaerobic. However, About ~3.2 billion years ago, fossil evidence of photosynthetic bacteria, or cyanobacteria, appears. These bacteria use the sun's energy to make sugar. Oxygen, released as a waste product, began to accumulate in the atmosphere. However, oxygen is actually pretty toxic to cells, even our cells! As a result, anaerobic cells were now a disadvantage in an oxygen-containing atmosphere, and started to die out as oxygen levels increased.

    Aerobic bacteria appear in the fossil record shortly after that (~2.5 Billion years ago). There cells were were able to use that 'toxic' oxygen and convert it into energy (ATP) and water. Organisms that could thrive in an oxygen-containing atmosphere were now 'best suited to the environment'. Aerobic eukaryotes appear in fossil record shortly after that, (~1.5 billion years ago). These cells contain either mitochondria, or both mitochondria and chloroplasts. The mitochondria and chloroplasts have their own genomes, but can not live outside their host cell."

    from "The Endosymbiotic Theory," IUPUI Dept. of Biology, February 18, 2004
    http://www.biology.iupui.edu/biocourses/N100/2k4endosymb.html

    "" - Early cells arranged in a filament at Warawoona, 3.5 BYA (billion years ago).
    - Stromatolites (mounds of photosynthetic cyanobacteria) 2.7 billion years old.
    - Intact stromatolites present today in Shark's Bay." (Western Australia)

    from "Origins of life," lecture notes by Bruce Walsh, University of Arizona, 1995.
    http://nitro.biosci.arizona.edu/courses/EEB105/lectures/Origins_of_Life/origins.html

    Life on earth originated about 3.86 billion years ago. Aerobic organisms (life that requires an oxygen environment) evolved about 3.2 billion years ago. Since we have fossil evidence dating back 3.5 billion years ago, then this fossil evidence might be anaerobic (from life that does not require an oxygen environment. Oxygen started to accumulate in te environment 3.8 billion years ago, but at very extremely small concentration levels - nothing like the amount of oxygen in the air we breath on earth today. So I guess its up for debate whether or not this life was aerobic or anaerobic.
     

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