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Climate Hustle

So what did-in the dinosaurs? A murder mystery…

Posted on 12 March 2015 by howardlee

Scientists have assembled a slew of new forensic evidence – from high-resolution dates to microscopic fossils – to prosecute the dino-killer. Their indictment has worrying implications for us.

Everyone knows that the dinosaurs were wiped out - along with about 70% of all species - by a massive asteroid slamming into Mexico, right? Well, not so fast. Like a good murder-mystery, a steady drip of evidence and some major new revelations have implicated another suspect – were they in it together or is one innocent?

Dead dino

Suspect A – the impact

Our first suspect is the asteroid impact at a place called Chicxulub, in Mexico.

This one is not a serial killer. In all the episodes of mass extinction through deep time, it has only credibly been implicated in the end-Cretaceous catastrophe. It’s weapons of death include a violent blast that destroys everything for thousands of miles around the impact, a heat flash from the blast that incinerates everything in a similar radius, followed by a near-global rain of red-hot ejecta that turns the sky into a broiler (“grill” if you are outside the US) inflicting fatal burns and igniting a global conflagration. The blast, centered in shallow ocean, generates a colossal tsunami across the juvenile Atlantic and the shock wave triggers earthquakes and tsunamis around the world far more violent than the 2011 magnitude 9 Tōhuku earthquake in Japan. Finally, the great quantity of dust and incinerated debris flung into the upper atmosphere blocks out the sun, turning the world dark and the climate frigid for years.

That should do it.

Except lately the idea that the impact’s heat flash could ignite everything has been challenged by experiments, which show: “any fires ignited by impact-induced thermal radiation cannot be directly responsible for plant extinctions, implying that heat stress is only part of the end-Cretaceous story.” Plant fossils around the world also show no sign that fire was above normal levels at the time. So that’s one weapon that probably didn’t cause global extinction. Neither the blast, nor the extreme earthquakes would have been enough to cause a global extinction by themselves. What about the tsunami? Tsunami deposits have been identified around the Gulf of Mexico and into the Atlantic, but further afield the deposits are elusive. Even those in Mexico and in Texas can be interpreted, with convincing detail, as just normal sediments rather than tsunami deposits. So the tsunami was of doubtful reach, its rock evidence questionable, and it can’t have caused global extinction alone.

How about blanketing the planet in hot fallout? While it is true that tell-tale traces of apparent impact fallout (high concentrations of iridium, “shocked” quartz crystals, and tiny glass droplets called  “spherules” or “tektites”) have been found in many parts of the world, the physical layer of impact deposits dwindles from  a thickness of 2 meters (6 feet) around the Gulf of Mexico, to 3 to 5cm (1 to 2 inches) in Europe, and is apparently absent in China, Alaska, Japan and New Zealand. An iridium-rich layer has been detected across North America, Europe and North Africa, and as far afield as the India-Bangladesh border, but has not been reported from China, Alaska and Japan. So the fallout by itself does not seem convincing as a worldwide killer, and there has even been a suggestion that some of those fallout traces may be from volcanic eruptions rather than an impact.

Was the impact capable of causing the ocean acidification that bumped-off so many marine species?

Professor Toby Tyrrell of the University of Southampton, England, and his coauthors tested this. At the American Geophysical Union conference in December they revealed their dramatic answer: “no.”

The impact cannot feasibly have generated the ocean acidification that killed off calcifying marine species in the mass extinction.

They looked at a number of possible ways the impact might have acidified the ocean. Did the impact’s pressure wave turn nitrogen to nitric acid? If it did, it didn’t generate enough to acidify the ocean. Vaporization of carbon from limestones at the impact site? Not enough. Liberation of carbon from terrestrial decay, soil respiration, wild fires, hydrocarbons? Nope. Tsunami stirring the oceans? No. All of the above together. Still no. Sulfur vaporized from the sulfur-rich rocks at Chicxulub and sucked into the atmosphere? It would take 800 billion tonnes of sulfate to achieve the acidification observed, but to get that number you have to max-out every assumption in the calculation to a ridiculous extent. So no, not even close. The impact cannot feasibly have generated the ocean acidification that killed off calcifying marine species in the mass extinction.

That just leaves the “impact winter” as our suspect’s last remaining, potentially globally-fatal weapon. But plant fossils around the world show that any impact winter severe enough to prevent plant growth can’t have lasted more than a couple of years. Maybe a couple of years was enough? Sediments in Texas and New Jersey do show a strong cooling spike thought to represent the transfer of cold impact winter atmospheric temperatures into the ocean, within months to decades after the impact. But it takes many decades for the ocean to cool or warm significantly, due to its great volume and thermal inertia. Such a brief climate blip is unlikely to have cooled oceans globally fast enough to produce the rapid, sharp cooling spike observed in the sediments. In any case, large eruptions are known to cause temporary climate cooling too. In the absence of any other corroborating evidence, the impact winter seems busted as an effective cause of global extinction by itself.

So, despite its murderous image, the Chicxulub impact seems to lack WMEs (Weapons of Mass Extinction). What about our other suspect?

Suspect B – climate change caused by massive volcanic eruptions

This one has a rap sheet as long as your arm. Unlike asteroid impacts, this suspect is a known serial killer, linked to four of the “big five” mass extinctions, as well as many other global extinctions and global warming events. Still, we should presume innocence until guilt is proven.

The Deccan eruptions in India were in a rare and exotic league of hyperactive eruptions known as a “Large Igneous Provinces” not seen on the planet in the last 16 million years.  They inundated an area of India 3 times the size of Texas (or France) in superhot rivers and lakes of lava, including the longest lava flow ever measured (over 1500 km/930 miles) that only stopped when it reached well out into the ocean. Around 3 kilometers (2 miles) thickness of lava built up episodically in around 750,000 years, but at the time of the mass extinction there were four especially massive mega-eruptions packed into just a few millennia.

But it’s not the lava that kills on a global scale, it’s the gasses.

Artist's impression of a Large Igneous Province

Artist’s impression of a Large Igneous Province mega-eruption such as the Deccan eruptions. Horizontal scale is approximately 1,500 km (930 miles). Vertical scale is exaggerated - the top of the box is the stratosphere (about 15 km above the ground). The modern world’s largest volcano – Hawai’i’s Big Island - is shown for approximate scale.

At the cataclysmic onset of each mega-eruption, towering columns of ash and gasses (including steam, CO2, sulfur dioxide (SO2), chlorine and fluorine) rose to stratospheric levels, where they spread around the planet. The SO2 became sulfate aerosols, just as it does in large eruptions today, which acted as sunscreen to cool the planet for a few years (much like the impact winter), while the chlorine and fluorine may have decimated the ozone layer causing a dramatic increase in harmful UV radiation reaching the ground.

If any of this sounds familiar, it’s because we’re projected to do something very similar to ourselves if we continue CO2 emissions at the same rate as today

The Deccan gas emissions were so massive and rapid they outstripped the ability of the ocean and other feedbacks to absorb them – causing CO2 to build sharply in the atmosphere over a few millennia. As the short-term volcanic winter diminished, it unmasked the really lethal weapons of abrupt global warming and ocean acidification. The planet warmed by 8°C (14°F) on land and 4°C (7°F) in the oceans, while the excess CO2 dissolved in ocean water, turning it increasingly acidic. The sulfur gradually rained down as sulfuric acid, which pickled land and sea alike until oceans were acid enough to dissolve shelly sea life alive.

If any of this sounds familiar, it’s because we’re projected to do something very similar to ourselves if we continue CO2 emissions at the same rate as today (our CO2 emission rate is comparable to that from the Deccan eruptions).

So yes, the eruptions had effective WMEs (Weapons of Mass Extinction), and Large Igneous Provinces have a record of doing all of this before, such as in the end-Triassic and end-Permian mass extinctions.

Placing the suspects at the scene of the crime.

Since we are talking global mass extinction this isn’t so much a problem of where, as when. At the scale of many millions of years that geologists are used to working with, the dates calculated from radioactive element decay (“radiometric dates”) for the mass extinction, the eruptions, and the impact are near identical. But not quite near enough to rule our defendants either in or out.

To tease out which of our suspects caused the mass extinction, we need to refine the dates to within a few tens of millennia. Zooming up to that level of detail puts us in the blur of radiometric dating uncertainty, so scientists have to resort to forensic sleuthing using fossils, traces of orbital wobbles, and magnetic field reversals to narrow the timeframes. The inevitable discrepancies between different studies, locations, and between marine and non-marine rocks, make establishing definitive timelines like trying to find a level line across small boats bobbing up and down on high seas.

So it helps to have one fixed point to refer to. The official end of the Cretaceous is defined in northern Tunisia at the level of the mass extinction recorded by marine rocks. A kind of tiny shelly sea life called foraminifera (“forams” for short) frequently evolved new species with different shell shapes, so they can be used to establish “level” time zones. The Tunisian rocks show a changeover from the “CF1” to the “P0” fossil time zones at the end-Cretaceous as a marker of the mass extinction, which can be traced in marine rocks around the world, along with a distinct layer of clay with a red layer at its base and a spike in iridium levels, and a kick in carbon isotopes that shows a big upset in the global carbon cycle at that time.

But the best date of the end-Cretaceous so far is defined in non-marine rocks from Montana, sandwiched between the last appearance of Cretaceous pollen and the first post-Cretaceous pollen fossils, dated to 66.043 million years ago, with an uncertainty of 43,000 years in either direction. That date is within 5,000 years (effectively identical) to a date for tektites – traces of the impact – found in Haiti. That would seem to put the impact conclusively at the time of the mass extinction, but the marine fossils associated with those Haitian tektites are from a time zone at least 100,000 years younger, showing that those tektites must have been recycled by later sedimentary processes, and cannot give the true date of the impact.

The plot thickens.

Chicxulub wrongly convicted?

You might expect that the impact fallout would generate a clear global signal, a time “level” against which all other events can be compared, but sadly that is not the case. It turns out that the spherules, shocked quartz, and the iridium spike can all be moved by sedimentary processes and groundwater. Just as we saw in Haiti, a number of locations from New Jersey to the Caribbean, where the signs of impact were considered proof that the impact coincided with the mass extinction, have large gaps lasting several hundred thousand years up to 3 million years, spanning the crucial time period at the end Cretaceous! They can’t be used to narrow down the date of the impact either.

And what if there was a doppelganger – another impact that occurred around the same time generating some of the same signals, potentially throwing us of the scent? It turns out there was.

A smaller asteroid blasted a crater at Boltysh in the Ukraine, dated at 65.59 million years ago, with an uncertainty of more than half a million years in either direction, amply overlapping the events we’re investigating. It appears to have inflicted negligible ecological trauma beyond its local neighborhood, and fossils inside the crater show the Boltysh impact happened a few thousand years before the end of the Cretaceous. The Earth Impact Database shows that there are an additional 3 known (small) impacts that might possibly have occurred in this timeframe, but which are very imprecisely dated. In other words Chicxulub may have been the largest by far, but it wasn’t the only impact broadly at that time capable of generating similar tell-tale impact traces.

Sediments drilled from within the Chicxulub crater itself tell a remarkably similar story to that at Boltysh. Once thought to be the settlings from the immediate aftermath of the impact and tsunami, they have since been shown to include a regular marine limestone containing the distinct late-Cretaceous CF1 fossils - so the crater must have been formed before the end-Cretaceous mass extinction! Corroborating that, rocks from Texas and Mexico show that the impact fallout (in the form of the oldest layer of impact spherules) predates the mass extinction by more than 100,000 years!

So – amazingly - it looks like the Chicxulub impact has an alibi. It wasn’t at the scene of the crime during the mass killing, but what about our other suspect?

Chicxulub's alibi: it was before the main extinction event

The impact’s alibi – it was about 100,000 years before the end-Cretaceous mass extinction. Left: oldest spherule layer at El Peñon in Mexico (formed in the early part of the CF1 fossil time zone). Center: close-up of the spherule layer. Right: microscopic view of spherules bent round each other showing they were still hot and soft when they settled. Photo credit: Gerta Keller, Princeton University.

Incriminating volcanic-induced climate change.

At the end of last year some new radiometric dates were published for the Deccan eruptions that were 10 to 100 times more precise than previously-published dates, placing the start of the main phase of Deccan eruptions within 250,000 years of the mass extinction and showing that the eruptions continued through the extinction event. For a finer-grained link to the mass extinction we need those marine fossils – but the Deccan lavas were erupted on land. Fortunately at the fringes of the lava flows near the Bay of Bengal, sediments between and below the longest mega-flows are characteristic of the latest Cretaceous, and sediments immediately above the lavas have the distinct fossils of the very first post-Cretaceous time zones, showing that the marine mass extinction occurred during the mega-eruptions.

The isotopic makeup of marine fossils varies with temperature and changes in the ocean carbon cycle, giving scientists a picture of the fluctuating climate leading up to the extinction. There were 4 distinct global warming phases punctuated by cooler episodes. Sea levels rose and fell, while some land areas suffered severe drought. This “global weirding” tortured life through wild climate instability, culling biodiversity in mega-eruption steps, culminating in the most abrupt climate change and ocean acidification during the 4th mega-eruption. By its end most Cretaceous life was rubbed-out.

Most shelly creatures make their shells from calcium carbonate – chemistry that only works in alkali water with sufficient carbonate (a throwback to the Cambrian Explosion when seawater first turned alkali and animals had to evolve ways to deal with this new ocean chemistry). Ocean acidification was deadly for these creatures, to the extent that more than 90% of calcareous nanoplankton were wiped out, along with many more well-known, photogenic species like belemnites and ammonites.

On land, forests died across most of the world, moldered, and gave way to open land covered in ferns, although eastern Russian and Antarctic vegetation doesn’t seem to have been so severely affected. Fluctuating climate and drought prevented the return of forests for many thousands of years.

Gotcha!

new dates... do not support an impact as the cause of the environmental changes

An incredibly detailed set of dates has just been published for end-Cretaceous sediments, which contain dinosaur fossils, in Montana. What they reveal is a sequence that is “not obviously consistent with an instantaneous forcing mechanism.” In other words, they do not support an impact as the cause of the environmental changes recorded by the sediments! In fact the new dates fit very well with the rest of the evidence incriminating the Deccan eruptions.

In North America and Europe the dinosaurs were healthy and diverse right up to within about 200,000 years of the end-Cretaceous, at which point they disappeared. Mammals and amphibians continued but declined markedly through the final 200,000 years of the Cretaceous, coinciding with the Deccan eruptions. A very similar story is told by the fossils of India, where you see fossils of flourishing vegetation and abundant animals, including nesting dinosaurs, right up to the Deccan eruptions. Once the eruptions start, sediments between the lava flows capture life dwindling away like a tragic stop-motion film. Dinosaurs and forests are decimated by the onset of the eruptions about 250,000 years before the end of the Cretaceous. The few that survive don’t make it past the next eruption, disappearing from the Indian fossil record well before other reptiles like turtles and snakes. During the final 18,000 years or so of the Cretaceous, terrestrial plant life in North America declines up to the end-Cretaceous boundary, matching the timing of the marine extinction and the Deccan mega-eruptions.

So it seems that the eruptions, not the Chicxulub impact, did-in the dinos, just as they dispatched so much other life on land and in the seas.

Verdict

So we have reached a verdict. All rise.

Deccan eruptions - for the Cretaceous global warming, ocean acidification, and extinction in the marine realm: guilty! For the terrestrial extinction including the dinosaurs: also guilty – but some may still claim reasonable doubt.

Chicxulub impact – for the Cretaceous global warming, ocean acidification, and extinction in the marine realm: not guilty! For the terrestrial extinction and doing-in the dinos: not guilty - It has an alibi, and there’s insufficient evidence of its ability to kill on a global scale to prosecute. After 30 years it’s time to let this one go. It has done its time.

Case closed? Probably not. There’s room for appeals and fresh evidence in the years ahead – perhaps even a “Serial” podcast. But the many strong strands of scientific evidence that global warming and ocean acidification was behind the demise of so much life, including the dinosaurs, should give us pause.

____________________

Hat tip to the Geological Society of America Special Paper 505, the Geological Society of America October 2014 meeting in Vancouver, the American Geophysical Union December 2014 Conference, to NPR’s “Serial” podcast, and to Professors Toby Tyrrell and Gerta Keller for several clarifications, corrections, and explanations.

Howard Lee’s latest book is “Your Life as Planet Earth,” an account of past climate changes, how they affected life, and how Earth and life affected climate.

The theory that the end-Cretaceous mass extinction was due to global warming and ocean acidification goes all the way back to 1978 with the publication of a paper by Dewey McLean in Science. Even back then Dewey saw the parallels to modern climate change. When Alvarez et al published their theory that an impact was the cause, this captured the public’s imagination, but debate continued and became rancorous enough to make the newspapers. When the previously identified Chicxulub crater was linked to the extinction in 1994 the impact theory became mainstream, yet it didn't completely match the observations.  So a new theory that combined the Deccan eruptions and the Chicxulub impact was developed, which has been generally accepted since 2008 (the Press-Pulse theory of mass extinction, where the eruptions pressed ecosystems to the brink before the impact pulse finished the job). In 2010, responding to papers by Keller, Schulte et al concluded that the impact was indeed the ultimate cause of the extinction, but the debate continued. The environmental data combined with the slew of high-precision dates since 2013 linking LIPs to mass extinctions in general, and the Deccan LIP to the end-Cretaceous specifically, has now shown the dominant role of the eruptions. But it’s fair to say that the timing and ecological trauma inflicted by the Chicxulub impact will continue to be debated and refined alongside the effects of the eruptions.

Citations:

MacLeod, N. (2014). The geological extinction record: History, data, biases, and testing. Geological Society of America Special Papers505, 1-28.

Alvarez, L. W., Alvarez, W., Asaro, F., & Michel, H. V. (1980). Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science208(4448), 1095-1108.

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Schulte, P., Alegret, L., Arenillas, I., Arz, J. A., Barton, P. J., Bown, P. R., ... & Willumsen, P. S. (2010). The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary. Science327(5970), 1214-1218.

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Mateo, P., Keller, G., Adatte, T., & Spangenberg, J. E. (2015). Mass wasting and hiatuses during the Cretaceous-Tertiary transition in the North Atlantic: Relationship to the Chicxulub impact?. Palaeogeography, Palaeoclimatology, Palaeoecology.

Keller, G. (2014). Deccan volcanism, the Chicxulub impact, and the end-Cretaceous mass extinction: Coincidence? Cause and effect?. Geological Society of America Special Papers505, 57-89.

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Huang, C., Retallack, G. J., Wang, C., & Huang, Q. (2013). Paleoatmospheric pCO 2 fluctuations across the Cretaceous–Tertiary boundary recorded from paleosol carbonates in NE China. Palaeogeography, Palaeoclimatology, Palaeoecology,385, 95-105.

Sial, A. N., Chen, J., Lacerda, L. D., Peralta, S., Gaucher, C., Frei, R., ... & Belmino, I. K. C. (2014). High-resolution Hg chemostratigraphy: A contribution to the distinction of chemical fingerprints of the Deccan volcanism and Cretaceous–Paleogene Boundary impact event. Palaeogeography, Palaeoclimatology, Palaeoecology414, 98-115.

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Zeebe, R. E., Dickens, G. R., Ridgwell, A., Sluijs, A., & Thomas, E. (2014). Onset of carbon isotope excursion at the Paleocene-Eocene thermal maximum took millennia, not 13 years. Proceedings of the National Academy of Sciences,111(12), E1062-E1063.

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Comments 1 to 50 out of 94:

  1. Thanks. I always find myself treating the end-Cretaceous extinction as the exception to the general rule that mass extinctions have been caused by GW, which was too bad, since it's the only mass extinction event that most people (think they) know something about.

    Now I can just point to this article.

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  2. Yes there's a pretty strong pattern. I think the end-Ordovician is now perhaps the only exception of the phanerozoic, linked by some to the first spread of vascular plants causing CO2 reduction and Global Cooling, resulting in the Hirnantian Glaciation.

    John Mason has a post due out soon on the Permian Mass Extinction - the most extreme example.

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  3. I'm not a scientist so am free to speculate:  If you tunnel through Earth to the spot opposite the Chicxulub Crater, you will be in the Indian Ocean.  Hmmm.

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  4. Thank you!  A most interesting article that takes me back to early undergraduate lectures nearly 4 decades ago. Another for the recommended reading list.

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  5. I remember two articles in Scientific American in the 1980s explaining the rival theories. The Deccan Traps were advanced as the alternative to the asteroid. It was a little shocking to read a popular very media-friendly theory attacked. Over the years I assumed the volcano account had receded or been discounted. Great article.

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  6. Don't know if this is on topic but I've heard that the atmosphere may have been thicker during that epoch. If it were would that have made a difference? How would the atmosphere have been affected by such an impact?

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  7. Amazing, interesting, informative, educational, and I'm 67. Thank you very much. 

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  8. To me this is as momentous a geological mystery as the story of Continental Drift.  Then there were many different arguments from various fields, though they all led to one conclusion, that was eventually observed - in the spreading sea floor under the Atlantic ocean.  The dinosaur whodunit is more traditional, with multiple suspects.

    It's inevitable that geological research will be done more with lab coats and a little less with boots on the ground.  That's where the answers lie.  But to this observer part of the appeal of geology was its simplicity, that resulted in part from the greater unknowns.  Just following fossils and formations, looking for an informative outcrop.  And what's on top is younger.

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  9. ubrew12 - great minds think alike, so they already looked into the idea that Chicxulub triggered the eruptions ("antipodeal focusing"), but no. Adrian Jones looked into that in his recent paper and concluded that earlier work was correct in establishing that India was in the wrong place at that point in its continental drift. The forces in rock opposite a Chicxulub impact are also apparently not quite enough to fracture rock. If they coincided with an area primed for an eruption anyway they might just set it off, but otherwise not.

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  10. Villabollo - I don't know that the atmosphere in the Cretaceous was thicker (assuming you mean height of the atmosphere, rather than density) - perhaps someone else can chime in. The height of the troposphere - the layer with sufficient density to make a difference to the asteroid - is about 7-20km. An asteroid travelling at cosmic speeds of about 30,000mph (48,000kph) would travel through that in about 1.5 seconds. Even if the height of the troposphere was higher I doubt it would make much difference.

     

    If you feel like an amusing exploration of this theme check out this "What if" post

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  11. Thanks Howardleevery thorough,interesting to read and insightful.

    And very scarey!

    Aren't we putting something like 3xmega eruption ratesof CO2, not to mention, SO2, CFC's for ozone, and a wholehostofother very toxic stuff into the world ecosystem and all at a rate imagineably quickly and from a low CO2 start (meanign CO2 input has more warming potential)..

    If we have any ancestors they really are going to wonder..

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  12. Ranyl - basically yes! The late Cretaceous, before the eruptions, was quite cool, with some suggestion there was even ephemeral ice in Antarctica. But the climate was overall warmer than the 20th century and CO2 levels higher. Ocean currents were also different as Antarctica was still connected to South America and Australia. So there were important differences between then and now, but the fundamentals of rapid greenhouse gas emissions and pollution leading to abrupt climate change, acidification and environmental disaster are the same.

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  13. Thanks howardlee, can't wait to tell my science loving 11 year old daughter about this great example of scientific process in action.

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  14. One of the funnest, most informative, article I have read here; moving first graphic;).

    Such a broad perspective brings up two questions 1) Is there a periodicity to asteroid "storms"? It'd be kind of like we have shooting star storms, but for different causes. 2) Does climate affect volcanism and seismicity?

    The argument here is that volcanism affects climate, but the other seems just as likely to me through GIA, it just conjecture on my part, but the science seems to be moving in that direction.

    Thus we could have feedback mechanisms between, cosmic periods, volcanism, climate change, back to volcanism, then climate change again. I call this idea, complex medium waves (CMW), because the period may be affected by chemical changes in the lithosphere, thus magma chemistry and flow characteristics. This may take tens of thousands of years, so it may fit well in this argument.

    It is just conjecture on my part because I have no education, and little study along those lines, but I am very curious to know more. This story is very helpful, especially with the rich sources. Nice work.

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  15. howardlee @ #10:

    Yes I know. What I was wondering was whether a substantial part of the atmosphere would have been ejected into space making our current atmosphere thinner than before. I didn't find a comment on the effects on the atmosphere in the link you cited.

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  16. @ ubrew12

    Why would a body, such as an asteroid, exit at the antipodes of its impact point?

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  17. Villabolo @15: All I have found is this paper researching the atmospheric "erosion" by the Chicxulub impactor. It states that "no more than about 7% of the vaporized bolide plus atmospheric mass will escape the gravitation of the Earth," in other words there will be a net gain, not loss, of mass. As they say in the title - surprising!

    Massive atmosphere loss happened at the time of the formation of our moon, mainly by a thermal process called "Jeans escape." That drove off our first atmosphere and replaced it with rock vapor, until volatiles expelled by cooling magma replaced it. But Earth retained a substantial atmosphere through the Late Heavy Bombardment,when the planet was pelted with large asteroids. This paper suggests there was probably a net gain of atmosphere through that time, in agreement with the paper above.

    We had a number of very large impacts since then (Manicouagan, Acraman, Popigai, Sudbury, Vredefort, and Chicxulub) with no reports of anything suggesting significant atmosphere loss.

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  18. Pluvial @ 14:

    On climate afffecting volcanism yes there is, but in a tiny way. The first is a feedback in which melting ice reduces pressure on magma chambers in glaciated parts of the world, encouraging them to erupt. Example: Iceland today. The other is in rising sea levels supressing mid-ocean-ridge volcanism (and the converse). This is a mild, slow, long-term negative feeback completely dwarfed by human emissions. Minus the cosmic periods, your complex medium waves idea is very similar to this feedback.

    Asteroid storms - I have seen a suggestion of long term periodicities in asteroid impacts but would have to dig further to find that paper. As is clear in the article, there is no evidence that they have much effect on the inner workings of the Earth or even its long-term climate, which is surprising.

    Cosmic periods - there was a suggestion a while back that there was a periodicity in the cosmic ray flux into the atmosphere based on the motion of our solar system through the arms of the Milky Way galaxy, but that has been refuted by more accurate mapping of the arms and our place within them.

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  19. @ funglestrumpet #16

    I'm pretty sure that ubrew12's point was that a longitudinal shock wave emanating from Chicxalub could have had percussions (pun intended) at the hot spot responsible for the basaltic mega-eruptions at the Deccan Traps. I don't for one moment think that some form of planetary-scale exit-wound was being mooted.

    I once did some sums in preparation for an astronomy presentation, and calculated that the kinetic energy of the impactor was roughly equivalent to the total solar energy hitting TOA for about one month. The term "made the planet ring like a bell" is one that I have seen applied to this little nudge.

     

    @ Howard

    One of my chums, sadly no longer with us, was a Fellow of the Geological Society of London, and he always had a soft spot for the Deccan Traps as the "culprit".

    There is, of course, another "suspect" - namely the so-called Shiva Crater Impact Spot. Does this have any real support in the rock-bashing community? (Those with any familiarity with the Hindu pantheon will appreciate the name.)

      cheers    bill f

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  20. @PluviaL #14

    Last year I went to a lecture given by Bill McGuire, the Emeritus Professor of Geophysical & Climate Hazards at University College London. His talk was entitled "Waking the Giant", and it examined the effects wrought by isostacy as a direct consequence of past climate change. (And I've got a signed copy.)

     

    cheers   bill f

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  21. Excellent article Howardlee.

    Always wondered about an asteroid impact being solely to blame for the extinction of the dinosaurs. This thesis seemed to become entangled with the nuclear winter arguments regarding the impact of a nuclear war.  Hence the reason it became the accepted idea  as to what caused the demise of the dinosaurs. I would have thought that if there had been significant climate cooling due to blocking out the sun from the aerosols ejected into the atmosphere from an asteroid impact, then there would have been a significant drop in the CO2 levels due to the reduced activity of plants before the vulcan outgassing of CO2 had its full impact. A large asteroid impact on the scale of Chixulub should have a similar climate impact as a single LIP, and it seems that you need a few LIPs occuring over a short geological period to actually trigger a mass extinction event.

    Perhaps, now that it is possible to date geological evidence more accurately, then a more refined history of of the sun's orbital dynamics, maturity and radiation levels; atmospheric composition; continental drift; vulcanism; climate change; and extinction events can be done. This may help put some of these controversies to rest.

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  22.  Thanks Howardlee, it is further;y concerning that for this Co2 induced warming assault on biodiversity that the earth has already lost 30-50% of its biodivesity and has extinction levels that geologoically noteable, before the warming infliuences are even really starting to bite.

    For an analogy it seems we've given th eearth leuakeamia and now its caught a high fever producingknown to be deadly virus.

    Whilst our dicision makers moan about 2C cuts and many of the so called solutions are laced with mining, toxic waste and have direct biodiversity harming impacts (e.g. PV panels).

    Seems Volacnoes could possibly be woken up on land but put to sleep in the ocean.

    WOnder if th erate of change in the oceans weight and uplift make any difference?

    Wonder if the the rate melt makes any difference?

     

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  23. @ billthefrog #19

    Thanks! I never thought of that. It makes a lot of sense.

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  24. @ 18, 20, Thanks for the info. I just ordered "Waking the Giant" looks really interesting. I expect that this view will grow as we get more information about this feedback loops, and more interest on the subject. The idea seems to alwasy be played down. I remeber seeing an article on GIA in which the authors concluded that since the chemical changes in the rock only went so far, that the effect could not have gone furhter. That seems narrow minded. Heat, and mechanical distortioins might be expressed otherwise. Bill McGuire, also poopoos the idea that the feedback loops may go far from the source. My expectation is that it is way underestimated. Exited to read his book soon.

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  25. Chicxulub, Deccan Traps & K/T Extinction =  Approx 65MYA   
    Tungusta = c.3 to 3 MegaTonTNT and Flattened 2,000 km2 forest Chicxulub = 1.30x10^8 MT-TNT = c.10^8 times Tungusta Energy Chicxulub Impact Angle = 90°
    Deccan Traps = 1,500,000 km2 Lava Flows  
    India's Global-position on Earth 65MYA = Opposite side from Chiculub
    IMO Chicxulub caused Deccan Traps Volcanic Activity.   
    CONCLUSION?  BOTH Chicxulub & Deccan Traps had V.Serious Impacts upon Life/Climate from: (A) Widespread Impact Zone and (B) Magma Fields, and, (C) Particulate Emissions Blocking Sun's Radiation - Which in turn caused (D) Global Freezing; thus killing all Dinosaurs as well v.strongly affecting: Plankton, Tropical Invertebrae, Land Plants, Etc.

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  26. I have always been skeptical of the impact hypothesis. It's interesting that these developments have not made it to the mainstream media, which always talk about the Chicxulub impact being responsible as if it were as certain as the law of gravity.

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  27. Excellent article - thank you for putting it together.

    One thing that always puzzled me -— why in the world would avian dinosaurs survive but the non-avian ones become extinct. Does the Deccan trap model offer any insight?

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  28. Similarities and varying hypotheses aside, some differences between modern birds and non-Avian Dinosaurs are significant.  Non-avian dinosaurs, previously presented as being "Cold Blooded", were still not "Warm" Blooded as Birds and Mammals are.  The enormity of Chicxulub (estimated to have possessed roughly 100 Million times the Energy of a 1 MegaTon H-Bomb) - cannot be ignored.    It left a crater upwards of 190 miles in diameter!   Imagine its Shockwave and Ejecta!    Same thing with Deccan Traps Volcanic Activity - leaving more than 1 mile thick of basalt lava over 100's of 1000's of km2.   Occurring at roughly the exact time as Chicxulub and the date of the End of the Dinosaurs!   It's not an Either-Or matrix.   It's both!   Lastly.  We know from today's measurements that even Much smaller volcanic activity lowers Earth's Temperature - because of its blockage of Solar Radiation reaching Earth.   Both Major Events: Chicxulub and Deccan Traps, are clearly evidenced in the geological record as being virtually co-simutaneous.   Both, obviously, had a Major impact on the Biota.. 

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  29. Watchdog @ 25 - the dates have been refined since then. Also the idea of "antipodeal focusing" of impact energy has been ruled out by scientists who have looked at the association. See @9.

    Watchdog @ 28 - You are correct - there's a large crater and it must have been at least a regional disaster. But as I explain in the article, when the evidence for its global reach and its synchronicity with the mass extinctions is examined, it comes up short. Absolutely it's a puzzle, but one that fits in with the fact that the earth has been peppered with impacts (admittedly few as large as Chicxulub) throughout the phanerozoic, and so far none has been linked to a mass extinction except Chicxulub. The point of the article was to highlight that the previously assumed global impacts of the Chicxulub impact are not supported by the geological evidence reported to date, whereas the Deccan eruptions do have very strong date and environmental evidence supporting their role.

    As is so often the case, more research is needed, especially on the impact, its high-resolution absolute date, and it's effects.

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  30. Joe @ 27 - I have to admit that I just don't know. This post from 2 years ago has some intersting ideas, essentially (a) body size, (b) smart brains, (c) genetic 'evolvability'.  This paper suggests mammals may have survived by hibernating through the worst of the catastrophe (no explanation for birds' survival). This paper suggests that creatures able to sustain themselves by eating earthworms survived.

    The body size theory is interesting because when you look at the more recent PETM global warming event, evolution tended to select for small body size. But there were small dinosaurs in the Cretaceous, so that can't be the whole explanation. Over to the biologists on that one, but I'm not sure there are clear answers yet.

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  31. howardlee @ 29  I fully concur that Deccan Traps is (IMO at least part of) the demise of dinosaurs..  And, Yes, a quantification of the impact effects of Chicxulub are in order - in order to determine just how "regional" in size it was..  A very rough comparison of Chicxulub with the largest H-Bomb tested by the US (Castle Bravo - 15MT):  The area of Castle Bravo's crater is c.3.25 sq km, and its Zone of Destruction extended way beyond its crater.   The area of Chicxulub's crater  - variously estimated at 180-300 km in diameter - is, conservatively, 10,000 Times Larger than the area of C.Bravo's crater.  Tunguska's Energy (Siberia, 1908) is estimated as high as 30MT-TNT (similar to C.Bravo).  It leveled c.80 Million trees in an area of 2,150 sq km.  POINT?  The "region" of Destruction wrought by Chiculub must be far larger than "just" its crater.. 

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  32. @ watchdog

    Just to put some numbers to it...

    A one megatonne TNT energy release equates to about 4.2x1015 joules.

    According to figures I have seen, the Chicxulub bolide was estimated to have a mass of about 23/4 trillion tonnes and was shifting at about 20 km/sec (straight down). That equates to a kinetic energy conversion of about 5.5x1023 joules, and therefore suggests that the energy release was roughly equivalent to about 130 million megatonnes TNT.

    So it would probably have made for quite a good barbeque.

    As the legendary Tzar Bomba only (?) had a yield somewhere around 50 megatonnes, that's why Novaya Zemlya still exists.

     

    cheers   bill f

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  33. @ billthefrog .. Yes.  130,000,000 MegaTons is equivalent to 9 Billion Hiroshima A-Bombs (@ 15 kilotons apiece); nothing to sneeze at.
    Plate Tectonics of 65MYA place the Deccan Traps on the opposite point of the Globe from Yucatan!    Exact Aging of the Chronology of the Deccan Traps and Chicxulub remains IMO a subject of some science disagreement - such as indicated by extensive Geochronological research on Deccan Trap Aging from Kanchan Pande in Journal of Earth System Science.   ALSO, during that rough time, as one might anticipate from either Asteroidal and/or Volcanic Ejecta/Emissions into the Atmosphere, Earth's Temperature dropped by as much as 8°C - resulting in a lowering of the oceans by c.40 meters - a definite sign of glaciation//global freezing - all resulting in decreased habitable land, rainfall, vegetation, and death from all the above.

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  34. billthefrog@19 said: "Chicxalub could have had percussions... at the hot spot" Yup. As I said, as non-scientist, I feel free to speculate.  I was just speculating that maybe, given a molten core of a certain diameter, the shock of Chicxalub could have attenuated in solid matter, most probably, JUST outside that core diameter, and focused itself on a ring on the planetary opposite, of diameter commensurate with the diameter of that molten core.  But, no, likelihood that the two events are related remains extremely low.  Having said that, Dashiell Hammett would certainly have made that relation.

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  35. @ ubrew12 - Perhaps if a group of geophysicists were given access to a military ballistics testing facility, the Questions surrounding the Chiculub->Earth->Deccan Traps Connection? could be settled once and for all. 

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  36. I'm going to need a bigger recycle bin to handle the obsolete lecture notes I use in my climate change classes.  I just put forth the bolide theory in last week's session.  I have learned to warn the students that change is inevitable in the realm of good science, so an abiding speculation is a valuable asset.

    Thanks to the efforts at explaining the Deccan Traps events alongside the bolide impact and thanks for y'alls voluminous comments.

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  37. "According to figures I have seen, the Chicxulub bolide was estimated to have a mass of about 23/4 trillion tonnes and was shifting at about 20 km/sec (straight down). That equates to a kinetic energy conversion of about 5.5x1023 joules, and therefore suggests that the energy release was roughly equivalent to about 130 million megatonnes TNT"

    I'll take your words for it BtF.

    Really illustates just how lethal a large CO2 injection is.

    Mind you CO2 releases is the mechanism with the long rep for mass extinctions and near mass exticntions.

    And we've put 2billion Hirosh bombes worth since 1998 alone and lots of sulphur and aerosols, just like ahuge volcanic offgasing just we;'ve done it really really quickly in comparison to the past events.

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  38. The causes of the deaths of living organisms wrought by the Chicxulub Impact and the Deccan Traps Emissions are clearly manifold.  Here's another for instance: A paper published in Nature GeoScience by 12 scientists "Production of sulphate-rich vapour during the Chicxulub impact and implications for ocean acidification " indicates that huge amounts of Sulphur Trioxide were formed by the impact which in turn formed into Sulfuric Acid.. resulting in intense global acid rain, which for starters, is the major culprit in eliminating most of the planktonic foraminifera populations in the oceans. 

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  39. Watchdog @38 I assume you are referring to Ohno et al 2014. That's a paper looking at the nature of the aerosols generated by an impact. In the article you will see I reference newer research on the volumes of material and mechanisms of acidification showing that ocean chemistry rules out the impact as a feasible cause of the ocean acidification.

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  40. howardlee @39 - Yes. Thank you.    Returning to the topic of quantifying the impact effects and "region" size of Chicxulub I refer to a paper in _Meteoritics and Planetary Science_, "Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth", by Collins, Meloth and Marcus, which includes various physical results from 3 sizes of impactors; one the size of Chicxulub.  I note that its thermal energy alone estimated at a radius of 1,800 miles from its point of impact is 10 times the level which would cause 1st degree skin burns.   My Point?   I think we can agree that the 'regional' area of destruction wrought by Chicxulub covered a rather vast region; perhaps continentalish. 
    http://impact.ese.ic.ac.uk/ImpactEffects/effects.pdf

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  41. " It’s weapons of death include a violent blast that destroys everything for thousands of miles around the impact, a heat flash from the blast that incinerates everything in a similar radius, followed by a near-global rain of red-hot ejecta that turns the sky into a broiler (“grill” if you are outside the US) inflicting fatal burns and igniting a global conflagration. The blast, centered in shallow ocean, generates a colossal tsunami across the juvenile Atlantic and the shock wave triggers earthquakes and tsunamis around the world far more violent than the 2011 magnitude 9 Tōhuku earthquake in Japan. Finally, the great quantity of dust and incinerated debris flung into the upper atmosphere blocks out the sun, turning the world dark and the climate frigid for years."

    From main article Watchdog, not sure what your point that Howardlee hasn' taddressed really.

    Yes a big impact makes a lot of waves, just not enough apparently to wipe out life all over the earth, that takes a global cultprit, according the evidence presented and mulled over by those who drawn the conclusions Howardlee presents.

    That an impact of that size didn't induce the full mass extinction makes CO2 warming and acidification just more worrying really.

    Although despite that, if a comet was again coming our way everybody would pull together to try and do something about if ways could be found. Yet when it comes to the greater threat posed by what we are doing, most people turn a blind eye, under the premise that an acclerated mass extinction won't happen really, the threat isn't that great, it won't happen to me or will take place in a far away place.

    Every year we pump out enough CO2 to be equivalent of approximately 3 mega volcanoes erupting.

    But the affects are too subtle as yet for most human's contemplation and threat reaction to be induced as we human's really only react to comet like threats, as we can identify the danger as an immediate impact and that is clearly life threatening.

    Anyway the scale of change required to actually become a sustainable, non toxic, biodiversity enhancing global soceity is too great it seems and the majority of solutions are still toxicity producing, biodiversity impacting and totally none sustainable (e.g. larges scale dams, wind turbines, PV panels, Batteries, industrial scale biomass production) and don't address the issues of massive over exploitation of resources, population expansion, waste creation and inasive alien species.

    We'd have more chance if a comet was going hit us!

    Does anyone out there actually think transformational change is possible if that meant sacrificing the car, plane and mobile phone?

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  42. Ranyl - Thank you for posting that selection.   "" It’s weapons of death include a violent blast that destroys everything for thousands of miles around the impact, a heat flash from the blast that incinerates everything in a similar radius, followed by a near-global rain of red-hot ejecta that turns the sky into a broiler (“grill” if you are outside the US) inflicting fatal burns and igniting a global conflagration. The blast, centered in shallow ocean, generates a colossal tsunami across the juvenile Atlantic and the shock wave triggers earthquakes and tsunamis around the world far more violent than the 2011 magnitude 9 Tōhuku earthquake in Japan. Finally, the great quantity of dust and incinerated debris flung into the upper atmosphere blocks out the sun, turning the world dark and the climate frigid for years.""   Please pardon me for my redundancy; however if you review that selection you can see it directly supports the fact that Chicxulub was a global event.  One can only surmise the actual and complete extent of all its immediate destructive-to-life effects upon life in North & South Americas'.  I.E.  It's clear from that selection is that its impact upon E.G., Global Temperature aka Global Freezing which is Not due to CO2 (and similar Solar-Radiation reduction effects from Deccan Traps Ejecta) are but a part of All the overall causes of the deaths of the dinosaurs.  

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  43. This is an excellent up-to-date analysis of the current thinking of the mass extinction at the Cretaceous-Triassic boundary. It has been over thirty years since the bolide impact theory was proposed yet we still do not have a definitive answer to the extinction. I believe this is because neither the bolide impact nor the volcanic are the primary culprits in the mass extinction; they played a minor role and were caused by changes in the position of the Earth’s core elements.

    I believe the Gravity Theory of Mass Extinction explains all mass extinctions, which have the following characteristics, in addition to the extinctions caused by changes in surface gravity:

    1. Massive flood basalt volcanic eruptions which originate at the core-mantle boundary.

    2. Massive fluctuations of sea levels.

    3. Large carbon isotope excursion (the disassociation of methane from marine locations caused by the combination of low sea level and lower surface gravity and not by volcanism).

    Scientists have ignored the coincidence of these factors, which accompany all mass extinctions prior to about 30mya.

    https://www.youtube.com/watch?v=wHMAT_i3-KQ&feature=youtu.be

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  44. Theorist @43.

    In my posts above I've directly alluded to some of your 3 points.

    Placing carbon isotope excursion and lower surface gravity on the side burner for a moment, the following factors are not negated by them.

    Point 1 - There is evidence (not proof) that the shockwave of the Chicxulub Impact (which would have travelled in the direction of the Deccan Traps) must connect with effects upon Earth's Core-Mantle

    Points 2 and 3 - There is strong evidence/agreement that the emissions of both Chicxulub and Deccan Traps ARE the Cause of the lowering of Earth's Temperature by as much as 8°C, which in turn caused a lowering of the Ocean Levels by c.40 Meters, which in turn is consistent with widespread glaciation, which in turn is consistent with significant llfe extinction.

    Said another way, after all was said and done: If the effects of either/both Chicxulub's impact shock and thermal, along with the effects of its Ejecta upon Life - as well as - the probable greater effects from the larger volume of Deccan Traps Ejecta (including damaging respiratory effects on fauna and flora), the ensuing Global Freezing due to the blockages of Solar Radiation from both events - would have dealt an additional death blow to much of any remaining life. ----

    In this current 'climate' of concern of Warming, the attention given to Abrubt Cooling Events - including their extent and effects upon Life - can be oft be cast aside.

    Consider the last Glaciation period which ended c.12,500 yrs ago, created 10 Million Sq. Miles (in both hemispheres, including all of Canada) covered in ICE - all consistent with a 400' lower Ocean levels of the Oceans.

    Consider now the contribution of that Glaciation event to Extinction:

    Consider the Habitability of Life in Canada 20,000 years ago.

    Recalling All of Canada was covered in ICE, how many species can survive during longterm periods of ICE and only ICE

    Speaking of Gravity. Consider the decrease in Gravity in a large portion of Canada, particularly in the general Hudson Bay area. The ICE upon that area was as much as 3.7 km thick. This ICE depressed that area (which still slowly rises) by c.650'.

    An agreed _part_ of the "cause" of the decrease in Gravity is:
    The ICE compression pushed _aside_ some mass/material from underneath that area - thus lowering the mass/gravity of that area.

    Another theory of lowering "part" of the Gravity is referred to as "convection". Whereby moving magma currents pull tectonic plates downward thus removing mass and thus lowering Gravity from that area.

    Both theories are now considered together as explaining the total "missing mass/lowered gravity" of that area.

    ERGO: Getting back to Lower Temps, the abrupt decline in global temperature is the Cause of the increase of ICE; which ultimately affected - in part - the Gravity of some areas of Earth.

    As with theories which approach Chicxulub and Deccan Traps as connected to each other, is that Glaciation Period and Magma Convection Process - possibly connected?

    POINT? Again, there are multiple causes and climatic (and other) effects - often intertwined) which are detrimental to life.

    WHY should the Overall Cause of Dinosaur Deaths be approached as if a new plausible theory _must supplant_ other existing plausible theories of detrimental-to-Life Causes and Effects?

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  45. Watchdog @44

    Regarding your comments:

    Point 1- At the time of the bolide impact, Chicxulub was not anti-podal to the Deccan Traps. All of the continents were still positioned on one hemisphere of the Earth.

    Points 2 and 3 -Chicxulub and the Deccan Traps did have a profound effect on the Earth’s temperature. I’m not aware of any glaciation at that time. I wouldn’t conclude there was glaciation because of the drop in sea level because the theory I mentioned, I’ll call it the GTME, explains that when the Earth’s core elements move back toward Earth-centricity and surface gravity increases, sea levels near Pangea’s continental remnants must have lowered, as they did. The same type of massive sea level drop occurred at the P-T boundary for, I believe, the same reason it did at the Cretaceous-Triassic boundary. And, I’m not aware of any glaciation at that time.

    The gravity anomolies that you refer to in Canada and elsewhere are caused by crust compression from overlaying ice. This is far different and significantly smaller than those caused by the movement of the Earth’s core elements theorized by the GTME.

    Regarding your final statement about the dinosaur extinction, my belief, based on their gradual extinction throughout the Cretaceous and the rapid disappearance of the remaining dinosaur taxa at the very end, cannot be explained by the bolide impact nor the volcanic theories or by attributing the extinctions to their combined effects. Dinosaur fossils have been found near the Deccan Traps between major lava flows raising doubt whether worldwide extinctions could have been the result of volcanism.

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  46. Theorist

    65 MYA, the continents were _Not_ positioned in one hemisphere.

    Please note India's position 65MYA wrt the Chicxulub's Impact site.  

    http://www.lpl.arizona.edu/~hubbard/PtyS195a/Mar06/Fig2-5globes.gif


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    Moderator Response:

    [PS] Fixed link.


    Creating a link isnt hard people. If you want people to see it, please do it as you make  comment.

  47. Watchdog,

    A better map can be found at www.scotese.com. Select "Earth History" and then "K-T Extinction" and you will see that the continents occupied close to one hemisphere. Also note the relative positions of Chicxulub and India.

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  48. Theorist @45, here are the continental configurations at the time of the K/T boundary according to Scotese:

    Based on that configuration, the Decan traps were as far south of the equator as the impact site was north of the equator, but 130 degrees of longitude west of the impact site, not 180 as require to be truly antipodal.  That compares with the modern arangement where they have approximately the same latitude but are approximately 180 degrees of longitude apart.  That means the divergence from the true antipodal point is about the same in both cases, having shifted from a divergence in longitude to a divergence in latitude.  Presumably the divergence is accounted for by assuming the impactor came in at a low angle, thus causing the point of focus to be shifted from the true antipodal point.

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  49. Theorist

    65 MYA, the continents were _Not_ positioned in one hemisphere.

    Please note India's position 65MYA wrt the Chicxulub's Impact site.

    http://www.lpl.arizona.edu/~hubbard/PtyS195a/Mar06/Fig2-5globes.gif

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    Moderator Response:

    [JH] Link activated.

  50. Watchdog @49, they were for the most part situated in one hemisphere delineated by longitude (ie, like the western hemisphere).  Theorist is correct on that point, if a little obscure.

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