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Author Topic:   The astronomical impact on terrestrial evolution
Briterican
Member (Idle past 2025 days)
Posts: 340
Joined: 05-29-2008


Message 1 of 15 (540866)
12-29-2009 3:43 PM


I'd be curious to hear what you guys have to say about the types and degree of impact (forgive the pun) that astronomical processes have had on terrestrial evolution.

Let's get two big ones which I know a little about out of the way first:

  • 1.Impact:

    Comets and meteors have pummeled the Earth and other surviving bodies in the solar system throughout its history. The evidence for this is overwhelming and some of it is quite literally under our feet. This would have been far more dramatic in the early stages of the formation of our solar system, when the number of bodies was greater and so then was the chance of impact. An equilibrium (of sorts) has been reached at the stage we now find ourselves, in which collisions are less common but still quite frequent in terms of the smaller meteorites that come down regularly.

    There is overwhelming evidence that collisions have caused mass extinction events on the Earth. These would dramatically alter the potential course of evolution, resetting the parameters for survival and ending any hopes of it for a great many in one violent second.

    Additionally, the very nature of this violent early stage may have prohibited early life from getting a foothold:

    Paul Davies writes:

    If Earth was pounded as fiercly as astronomers believe, and if surface organisms really were well-established by 3.8 billion years ago, then life must have burgeoned almost as soon as the effects of the last sterilizing impact were over.

    Citing a study by Kevin Maher and David Stevenson from Caltech, the author goes on to discuss the possibility that life may have arisen in between cataclysmic periods only to get repeatedly wiped out:

    Paul Davies writes:

    "It is a curious thought that if life did form anew several times, then humans would not be descendants of the first living thing. Rather, we would be the products of the first life forms that just managed to survive the last big impact in this extended stop-go series."

    Davies eventually gets around this whole conundrum by presenting evidence that the earliest life forms may have been subterranean and capable of withstanding enormous heat and conditions that we would class as extremely hostile. Their closest cousins may be mirrored in the hyperthermophiles that we find today.

  • 2.Possible extraterrestrial origins of life:

    The idea here is that life arose on some body other than the Earth and was deposited here via impact. This idea most often involves comets, and it has been shown that comets contain a great deal of organic material. It was confirmed earlier this year that the amino acid glycine was found in NASA's Stardust mission to Comet Wild 2 in 2004. http://www.newscientist.com/article/dn17628-first-amino-acid-on-a-comet-found.html

    This is a fascinating area in its own right, but it really simply redefines the location of origin of the earliest life, and not the subsequent terrestrial evolution which I am discussing in the post.

    The next two are where I definitely hope to hear what you guys think:

  • 3.The Moon:

    What effects has our moon had on evolution? There is an unmistakable connection between the moon and living things due to its gravitational pull (tidal patterns, menstrual cycles).

    In what other ways has the moon influenced natural selection on Earth?

    The reflected sunlight from the moon that comes and goes over the course of a month has undoubtedly played a role in various ecosystems, even if just by virtue of providing better light by which to hunt and/or gather.

    The moon has undoubtedly played a large role in the cultures of human beings. I find it fascinating to think that it might actually have given us a head-start towards rationality in the sense that it provides a nearby reminder of order in the heavens, one that stands in stark contrast to the sun, and the two of which together provide an even greater insight to just what the hell is going on. What might it be like to evolve on a planet that had no moon? Or three moons? Would a three moon system have led to a more rapid understanding of physical laws, mathematics, astronomy?

  • 4. Earth's tilted axis

    What influence have the seasons on earth, thanks to its tilted axis, had on terrestrial evolution? Would it have been more advantageous to have had no tilt? Or, did this fact play a crucial role in evolution by driving adaptive features?

  • 5. What else?

    What other aspects of our astronomical history have impacted the course of evolution on Earth, and what might life be like if conditions had been otherwise?

    (--- Science: human origins and evolution forum? That would be more accurate than big bang/cosmology, please ---)

    Edited by Briterican, : Title change, note to admin re desired forum.


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    Message 2 of 15 (541082)
    12-31-2009 8:43 AM


    Thread Copied from Proposed New Topics Forum
    Thread copied here from the The astronomical impact on terrestrial evolution thread in the Proposed New Topics forum.
        
    Iblis
    Member (Idle past 1972 days)
    Posts: 663
    Joined: 11-17-2005


    Message 3 of 15 (541251)
    01-01-2010 7:54 PM
    Reply to: Message 1 by Briterican
    12-29-2009 3:43 PM


    More abiogenesis
    This is an excellent topic idea!

    To your point 2 regarding the largely unsupported theory that life may have come to earth in the form of microbes riding on a comet's tail or Martian meteorites, I would like to add a couple of more substantial suggestions:

    First, the near-ubiquitous "starseed transmissions", ie that the complex molecules which contribute much to our chemical composition are revealed by spectrographic analysis to be products manufactured by the sun, and therefore came to us either as a result of previous supernova events or else due to yet-unspecified stellar explosions or expansions on a more local level;

    And second, that the current best candidate for a "natural" PNA, polycyclic/nuclear aromatics (PAH), known to be common in the environment of early earth, were recently determined by similar spectro-analysis to be the product of distant nebulae; these guys are a real winner in terms of primitive information-binding, having not only a similar stacking pattern but one with the exact same "groove" size as the later, derivative molecules of nucleic acid.

    http://en.wikipedia.org/wiki/PAH_world_hypothesis


    This message is a reply to:
     Message 1 by Briterican, posted 12-29-2009 3:43 PM Briterican has responded

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    Briterican
    Member (Idle past 2025 days)
    Posts: 340
    Joined: 05-29-2008


    Message 4 of 15 (541281)
    01-02-2010 7:54 AM
    Reply to: Message 3 by Iblis
    01-01-2010 7:54 PM


    How important are the seasons, and the moon?
    Thanks for your reply Iblis.

    Doesn't seem to be much interest in the thread, but then it isn't really a debate topic or one that carries any controversy.

    Your point about nebulae is fascinating and I must admit I was not aware of this aspect.

    The thing that I wish someone would address is the impact of the moon, and the seasons, on evolution. I've been trying to find information on the net about this but have come up short. There must be some major connections between the seasons (via the tilt of Earth's rotational axis) and evolution. I would guess that seasonal changes have caused organisms to adapt to the changing conditions, and possibly even to develop cyclical patterns that run in conjunction with the seasons. There's bound to be examples of this in nature.

    I also wish I understood more about the connection of the moon to biology on the Earth. Menstrual cycles are just one example of a direct connection between the moon and biology on the Earth, and I am curious if any research has shown how the moon's tidal pull may have impacted the evolution of these cycles in Earthbound creatures.

    Chances are the thread will die a quiet death hehe, but if anyone can point me in the right direction for further information on these connections I'd be grateful.


    This message is a reply to:
     Message 3 by Iblis, posted 01-01-2010 7:54 PM Iblis has responded

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    Iblis
    Member (Idle past 1972 days)
    Posts: 663
    Joined: 11-17-2005


    Message 5 of 15 (541299)
    01-02-2010 12:05 PM
    Reply to: Message 4 by Briterican
    01-02-2010 7:54 AM


    Re: How important are the seasons, and the moon?
    Sorry I didn't link the actual discovery part before

    http://en.wikipedia.org/...atic_hydrocarbons#Origins_of_life

    In January 2004 (at the 203rd Meeting of the American Astronomical Society), it was reported[11] that a team led by A. Witt of the University of Toledo, Ohio studied ultraviolet light emitted by the Red Rectangle nebula and found the spectral signatures of anthracene and pyrene (no other such complex molecules had ever before been found in space). This discovery was considered confirmation of a hypothesis that as nebulae of the same type as the Red Rectangle approach the ends of their lives, convection currents cause carbon and hydrogen in the nebulae's core to get caught in stellar winds, and radiate outward.

    This may have some application to your seasonal or cyclic interest, as meteor bombardments follow repetitive patterns.

    I also wish I understood more about the connection of the moon to biology on the Earth. Menstrual cycles are just one example of a direct connection between the moon and biology on the Earth, and I am curious if any research has shown how the moon's tidal pull may have impacted the evolution of these cycles in Earthbound creatures.

    I regret to inform you that some of your ideas about tides may be based on myth. You can see me ranting about this a bit more here. Message 433

    If you use reason in this matter, you will note that the menstrual cycle of cats and dogs is quasi-seasonal rather than quasi-lunar. In other words, whatever influence these cycles may have on reproductive biology is not a result of gravitational displacement somehow being directly apparent to the animal, nor is it derived from a period when we were single-celled or genuinely amphibious; it is more recent, and varies from species to species.

    This becomes clearer when we look at our relatives.

    The duration of the menstrual cycle varies with species; about 29 days in orang-utans, about 30 days in gorillas and about 37 days in chimpanzees. Incidentally, the duration of estrus also varies in these species; about 4-6 days in female orang-utans, about 2-3 days in gorillas and about 10-14 days in chimpanzees. Both the menstrual cycle and estrus vary in duration somewhat among females of the same species.

    http://pin.primate.wisc.edu/aboutp/anat/menstrual.html

    This implies that the cycles are derived only secondarily from the moon, specifically its light; and that their primary cause is due to longterm species hunting and eating behavior. Modern chimpanzees do not hunt.


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    slevesque
    Member (Idle past 2717 days)
    Posts: 1456
    Joined: 05-14-2009


    Message 6 of 15 (541316)
    01-02-2010 1:50 PM
    Reply to: Message 4 by Briterican
    01-02-2010 7:54 AM


    Re: How important are the seasons, and the moon?
    Aren't lunar tides supposed to have helped the mixing of the primordial soup to help abiogenesis ? I think I remember my astrophysics teacher saying something like that. Although it's not a clear memory at all so I may be wrong.

    Also, while reading your OP I did find that the ''overwhelming evidence fore multiple collisions that caused mass extinctions'' was a bit of elephant hurling, since the most supported one (dinosaur extinction) is still a pretty controversial theory in the scientific community. Never mind all the others. I couldn't say that any have overwhelming evidence.


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    Iblis
    Member (Idle past 1972 days)
    Posts: 663
    Joined: 11-17-2005


    Message 7 of 15 (541318)
    01-02-2010 2:07 PM
    Reply to: Message 6 by slevesque
    01-02-2010 1:50 PM


    The Big Smack
    Also, while reading your OP I did find that the ''overwhelming evidence fore multiple collisions that caused mass extinctions'' was a bit of elephant hurling, since the most supported one (dinosaur extinction) is still a pretty controversial theory in the scientific community.

    Here's the theory

    In 1980, a team of researchers consisting of Nobel prize-winning physicist Luis Alvarez, his son geologist Walter Alvarez, and chemists Frank Asaro and Helen Michel discovered that sedimentary layers found all over the world at the Cretaceous–Tertiary boundary contain a concentration of iridium many times greater than normal (30 times and 130 times background in the two sections originally studied). Iridium is extremely rare in the earth's crust because it is a siderophile, and therefore most of it travelled with the iron as it sank into the earth's core during planetary differentiation. As iridium remains abundant in most asteroids and comets, the Alvarez team suggested that an asteroid struck the earth at the time of the K–T boundary.

    Here's the data

    Subsequent research, however, identified the Chicxulub Crater buried under Chicxulub on the coast of Yucatán, Mexico as the impact crater which matched the Alvarez hypothesis dating. Identified in 1990 based on the work of Glen Penfield done in 1978, this crater is oval, with an average diameter of about 180 kilometers (112 mi), about the size calculated by the Alvarez team.

    And here's the controversy

    In 1997, paleontologist Sankar Chatterjee drew attention to the proposed and much larger 600 km (370 mi) Shiva crater and the possibility of a multiple-impact scenario.

    In 2007, a hypothesis was put forth that argued the impactor that killed the dinosaurs 65 Ma ago belonged to the Baptistina family of asteroids.

    http://en.wikipedia.org/.../Dinosaur_extinction#Impact_event

    There's a bit more here

    Several other craters also appear to have been formed about the time of the K–T boundary. This suggests the possibility of near simultaneous multiple impacts, perhaps from a fragmented asteroidal object, similar to the Shoemaker-Levy 9 cometary impact with Jupiter. In addition to the 180-km (112 mi) Chicxulub Crater, there is the 24-km (15 mi) Boltysh crater in Ukraine (65.17 ± 0.64 Ma), the 20-km (12 mi) Silverpit crater, a suspected impact crater in the North Sea (60–65 Ma), and the controversial and much bigger 600-km (370 mi) Shiva crater. Any other craters that might have formed in the Tethys Ocean would have been obscured by tectonic events like the relentless northward drift of Africa and India.

    http://en.wikipedia.org/..._extinction#Multiple_impact_event


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    Briterican
    Member (Idle past 2025 days)
    Posts: 340
    Joined: 05-29-2008


    Message 8 of 15 (541340)
    01-02-2010 4:15 PM
    Reply to: Message 5 by Iblis
    01-02-2010 12:05 PM


    Re: How important are the seasons, and the moon?
    Regarding the PAH world hypothesis, there seems here some amazing possibilities. I found this detail (from wiki) particularly amazing:

    In this self ordering stack, the separation between rings is 0.34 nm. This is the same separation found in RNA and DNA. Smaller molecules will naturally attach themselves to the PAH rings. However PAH rings, while forming, tend to swivel around on one another, which will tend to dislodge attached compounds that would collide with those attached to those above and below. Therefore it encourages preferential attachment of flat molecules such as pyrimidine and purine bases. These bases are similarly amphiphilic and so also tend to line up in similar stacks. This ends up making an effective scaffold for a nucleic acid backbone to form along the bases.

    A small change in acidity would then allow the bases to break off from the original stack of PAHs and so form molecules like RNA.

    I've seen the scaffolding idea mentioned before, but I've never heard of such a close fit as the 0.34nm mentioned above.

    The wikipedia page mentions that this is untested. I hope that, if any such testing is feasible, someone is working on it.

    Iblis writes:

    I regret to inform you that some of your ideas about tides may be based on myth.

    Now that you mention it, it seems like someone told me this before. I must not have been paying attention, but I am now. Feeling a bit silly about that now hehe, but hey... you've helped me shed another misconception so, that's good.

    Iblis writes:

    This implies that the cycles are derived only secondarily from the moon, specifically its light; and that their primary cause is due to longterm species hunting and eating behavior. Modern chimpanzees do not hunt.

    Yeah, I read the primate link and I see what you mean.

    Just for grins... check out this crazy quote from a website on menstruation

    *****Warning: the following is BS******

    Human beings are affected by the moon. Women especially are affected by the moon and their menstrual cycle is intimately linked to this celestial body.

    The moon:

    * regulates your menstrual cycle,
    * can trigger ovulation and fertile times,
    * affects your emotions and
    * affects the way people behave and view the world.

    Women are connected to the moon by our blood, our hormones and our souls.

    The first step in claiming the gifts of our menstrual cycle is to become re-acqainted with Mother Moon. Putting aside all the scientific phenomena of the way the Moon affects the earths tides, weather, animals, fluids and moods, symbolically the Moon has a lot to teach us.

    I think I can safely eliminate that site as a source of reliable information.

    I have instead found several sources confirming what you've said, such as this to-the-point quote from The Straight Dope:

    Cecil Adams writes:

    The smart money says it's coincidence.

    Thanks again for the replies.


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    slevesque
    Member (Idle past 2717 days)
    Posts: 1456
    Joined: 05-14-2009


    Message 9 of 15 (541341)
    01-02-2010 4:25 PM
    Reply to: Message 7 by Iblis
    01-02-2010 2:07 PM


    Re: The Big Smack
    Yeah I'm familiar with this. But my remark wasn't solely about this, it was about the fact that briterican was referring to multiple impacts that caused multiple extinctions, and that there was overwhelming evidence for this. It's pretty much a detail in the overall picture of his OP, but I figured I'd pick it up and mention it since his thread wasn't being discussed a lot.

    Now, in the case of the dinosaur extinction is one of the few (if not the only one) who could be said to have ''overwhelming evidence', although it would be quite an exageration in my opinion. We could discuss this particular case in this thread if Briterican doesn't mind.


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    Briterican
    Member (Idle past 2025 days)
    Posts: 340
    Joined: 05-29-2008


    (1)
    Message 10 of 15 (541343)
    01-02-2010 4:46 PM
    Reply to: Message 6 by slevesque
    01-02-2010 1:50 PM


    Re: How important are the seasons, and the moon?
    Hi slavesque

    slavesque writes:

    Aren't lunar tides supposed to have helped the mixing of the primordial soup to help abiogenesis ? I think I remember my astrophysics teacher saying something like that. Although it's not a clear memory at all so I may be wrong.

    Here's a quote from wiki on the "radioactive beach hypothesis":

    Zachary Adam at the University of Washington, Seattle, claims that stronger tidal processes from a much closer moon may have concentrated grains of uranium and other radioactive elements at the high water mark on primordial beaches where they may have been responsible for generating life's building blocks.[39] According to computer models reported in Astrobiology,[40] a deposit of such radioactive materials could show the same self-sustaining nuclear reaction as that found in the Oklo uranium ore seam in Gabon. Such radioactive beach sand provides sufficient energy to generate organic molecules, such as amino acids and sugars from acetonitrile in water. Radioactive monazite also releases soluble phosphate into regions between sand-grains, making it biologically "accessible". Thus amino acids, sugars and soluble phosphates can all be simultaneously produced, according to Adam. Radioactive actinides, then in greater concentrations, could have formed part of organo-metallic complexes. These complexes could have been important early catalysts to living processes.

    There seems to be plenty of notions about how life got its start, but they obviously can't all be right. I hope to live long enough to be here for a breakthrough in this field.

    Also, while reading your OP I did find that the ''overwhelming evidence fore multiple collisions that caused mass extinctions'' was a bit of elephant hurling, since the most supported one (dinosaur extinction) is still a pretty controversial theory in the scientific community. Never mind all the others. I couldn't say that any have overwhelming evidence..

    I probably use the term "overwhelming evidence" a bit too much. I'll watch that.

    However, given the iridium layer at the KT boundary, it seems that any controversy regarding the dinosaurs' extinction seems to be more about which impact(s) were responsible rather than were impact(s) responsible.

    Here's a quote from Richard Cowen of the University of California, in a paper titled "The KT Extinction":

    An asteroid big enough to scatter the estimated amount of iridium in the worldwide spike at the K-T boundary may have been about 10 km (6 miles) across. Computer models suggest that if such an asteroid collided with Earth, it would pass through the atmosphere and ocean almost as if they were not there and blast a crater in the crust about 100 km across. The iridium and the smallest pieces of debris would be spread worldwide by the impact blast as the asteroid vaporized into a fireball.

    It is an old paper (1999), but I'm not convinced that there is any ongoing controversy about the iridium layer. In other words I'm pretty sure that it is attributed to an impact as described above, and it just happens that before it are dinosaurs. After it, no dinosaurs.

    Thanks for the reply.


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    Briterican
    Member (Idle past 2025 days)
    Posts: 340
    Joined: 05-29-2008


    Message 11 of 15 (541344)
    01-02-2010 4:50 PM
    Reply to: Message 9 by slevesque
    01-02-2010 4:25 PM


    Re: The Big Smack
    slavesque writes:

    Now, in the case of the dinosaur extinction is one of the few (if not the only one) who could be said to have ''overwhelming evidence', although it would be quite an exageration in my opinion. We could discuss this particular case in this thread if Briterican doesn't mind.

    I'd be delighted, and again, Iprobably have used the term "overwhelming" a bit haphazardly.


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    Iblis
    Member (Idle past 1972 days)
    Posts: 663
    Joined: 11-17-2005


    Message 12 of 15 (541355)
    01-02-2010 6:38 PM
    Reply to: Message 8 by Briterican
    01-02-2010 4:15 PM


    Tide and Time
    Just for grins... check out this crazy quote from a website on menstruation

    Look, you understand that that site is about Magic, right?

    slevesque writes:

    Aren't lunar tides supposed to have helped the mixing of the primordial soup to help abiogenesis ?

    Now here we get to something where the tidal action has a real influence. Let's take a closer look at the dark hours of the pre-dawn of the PNA world

    In 1957, Sidney Fox demonstrated that dry mixtures of amino acids could be encouraged to polymerize upon exposure to moderate heat. When the resulting polypeptides, or proteinoids, were dissolved in hot water and the solution allowed to cool, they formed small spherical shells about 2 μm in diameter—microspheres. Under appropriate conditions, microspheres will bud new spheres at their surfaces.

    http://en.wikipedia.org/...Microsphere#Biological_Protocells

    Note that the amino acids form wet in the "soup". Then they have to be dry to become polypeptides. Then they have to be dissolved again to become microspheres. Further cycles of wet and dry are necessary for the best results in growing and budding.

    These protocells are baby genes, without NAs but copying rather than splitting. In some ways, the prions being discussed in Scripps Florida scientists show 'lifeless' prions capable of evolutionary change are a similar dealie, only reduced to parasitism. The microspheres are self-sufficient.

    Now let's look at where the real cell membranes come from.

    Waves breaking on the shore create a delicate foam composed of bubbles. Winds sweeping across the ocean have a tendency to drive things to shore, much like driftwood collecting on the beach. It is possible that organic molecules were concentrated on the shorelines in much the same way. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles composed mostly of water burst quickly, water containing amphiphiles forms much more stable bubbles, lending more time to the particular bubble to perform these crucial reactions.

    Amphiphiles are oily compounds containing a hydrophilic head on one or both ends of a hydrophobic molecule. Some amphiphiles have the tendency to spontaneously form membranes in water. A spherically closed membrane contains water and is a hypothetical precursor to the modern cell membrane. If a protein would increase the integrity of its parent bubble, that bubble had an advantage, and was placed at the top of the natural selection waiting list. Primitive reproduction can be envisioned when the bubbles burst, releasing the results of the 'experiment' into the surrounding medium. Once enough of the 'right stuff' was released into the medium, the development of the first prokaryotes, eukaryotes, and multicellular organisms could be achieved.


    http://en.wikipedia.org/...m_organic_molecules_to_protocells

    This shows a potential for tidal action to affect the formation of lipids containing these primitive proteins, which would reproduce by splitting. That's another step closer to "life as we know it."

    Your radioactive beaches are another good example, this time relating to the power source for nucleic acid formation. Some people prefer to point out that the existing archaea, the earliest form of "real" life, are famous as extremophiles and therefore probably developed using the energy of earth's magma. But even if this were the case, tides would still have an effect, as lava is a high-volume liquid subject to the usual gravitational displacement.

    There seems to be plenty of notions about how life got its start, but they obviously can't all be right.

    Sure they can! Or at least, a lot of them. See, they are talking about the origin of various components. Which one came first, and helped the others along, is what the argument might be about. I have skipped the "sandwich" beyond mentioning archaea, but pre-enzymes came from somewhere too, somewhere before RNA.

    Here, have a look at this. Pre-NA World

    Note that even once "life" finishes beginning, it remains in the oceans for billions of years. Tidal displacement remains a primary influence throughout this period. Once the weeds and then critters start swarming out onto the land, they continue to have a close association with bodies of water for millions and millions more. Most still do.

    Edited by Iblis, : context reduced


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    RAZD
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    Message 13 of 15 (541360)
    01-02-2010 7:02 PM
    Reply to: Message 10 by Briterican
    01-02-2010 4:46 PM


    impact on life? huge.
    Hi Briterican,

    There seems to be plenty of notions about how life got its start, but they obviously can't all be right. I hope to live long enough to be here for a breakthrough in this field.

    That was my opinion when I wrote Building Blocks of Life (2005), which also addresses the numerous prebiotic molecules found in space, and their riding to the surface of the earth during asteroid\meteor bombardment (especially in the early earth astronomical environment, when they were much more prevalent). Also see Message 15.

    However, given the iridium layer at the KT boundary, it seems that any controversy regarding the dinosaurs' extinction seems to be more about which impact(s) were responsible rather than were impact(s) responsible.

    There are also impact craters associated with other extinction events,

    http://www.nasa.gov/...04/may/HQ_04159_australian_coast.html

    Enjoy.

    Edited by RAZD, : m


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    Minnemooseus
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    Member Rating: 4.0


    Message 14 of 15 (541369)
    01-02-2010 8:53 PM
    Reply to: Message 10 by Briterican
    01-02-2010 4:46 PM


    The impact the period and not the whole sentence?
    It is an old paper (1999), but I'm not convinced that there is any ongoing controversy about the iridium layer. In other words I'm pretty sure that it is attributed to an impact as described above, and it just happens that before it are dinosaurs. After it, no dinosaurs.

    It is my recollection and understanding (no references at hand) that the dinosaurs were already in severe decline prior to the impact event, and that there was some minor post impact dinosaur survival. Still, the impact certainly seemed (weasel word alert) to pretty much put a period at the end of the dinosaur sentence.

    I wonder about (but am far too lazy to research) the the pre-impact environmental changes?

    Moose


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     Message 10 by Briterican, posted 01-02-2010 4:46 PM Briterican has acknowledged this reply

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    Iblis
    Member (Idle past 1972 days)
    Posts: 663
    Joined: 11-17-2005


    Message 15 of 15 (541373)
    01-02-2010 9:28 PM
    Reply to: Message 14 by Minnemooseus
    01-02-2010 8:53 PM


    Re: The impact the period and not the whole sentence?
    I wonder about (but am far too lazy to research) the the pre-impact environmental changes?

    Marine regression and increased volcanic activity. But there's a huge debate now as to how much of this was before the first impacts and how much was a result of it.

    Reductions in sea level wipe out marine species, reducing the food chain and oxygen supply. But many of the proposed impacts were into the ocean, so is it a cause or an effect?

    In much the same way, the Deccan Traps in western and central India show huge amounts of magma during this time period, indicating probably a genuine mantle plume. This sort of thing will produce catastrophic changes in the atmosphere of the whole planet. On the other hand, the Shiva crater is right off the coast there. What happens when you punch an orange?

    Still, the impact certainly seemed (weasel word alert) to pretty much put a period at the end of the dinosaur sentence.

    Not so much a period as an ellipse. The first impact, the iridium meteor, wreaked havoc on the biosphere. But further hits and resultant changes over the next 300,000 years are what kept them from coming back again the way they did after the Jurassic.


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