Problem 16: Multiple cosmic dust and Be-10 events are problematic for the supernova theory. Five of the eight Greenland polar ice dust samples I studied had been filtered from the ice by glaciologist Lonnie Thompson (1977) as part of his microparticle study and three I filtered myself from Camp Century polar ices. In his study, Thompson had found tin-bearing particles in 3 out of the 11 Camp Century, Greenland ice core samples he analyzed. My study confirmed the high Sn level he had previously observed in the 50,500 year b2k sample and also reported high concentrations in two other samples from his collection, (dating 38.65 and 78.5 kyrs b2k) which had levels too low for him to detect with his electron microprobe technique. Low levels of Sn, but again far above crustal abundance, were present in one other sample (49.5 kyrs b2k) that I had filtered from Camp Century ice. I also found high concentrations of iridium, nickel, and in some cases high levels of tin, in three Antarctic polar ice core samples, including a 31,500 year old dust band which I have listed in Table I along with the Greenland ET dust samples I processed as well as two samples (dating 17 and 125 kyrs b2k) for which Thompson had reported high levels of Sn in his 1977 study. I include these two in the list as well on the assumption that the Sn is an indicator for cosmic dust of anomalous composition. All together these comprise 9 cosmic dust horizons additional to the event found at the YD boundary.
     This evidence of multiple past cosmic dust incursion events raises a serious problem for the Firestone-West supernova-comet-explosion theory. For example, six of the dust events listed in Table I take place prior to the time of their proposed 41,000 years b2k supernova explosion date, which leaves these earlier events unaccounted for. Furthermore we should also add to the list of possible ET events the beryllium-10 concentration peaks present in the Vostok ice core record which date around 57, 64, 76, 97, 106, 117, and 133 kyrs b2k. So in all there may be at least 16 cosmic dust/cosmic ray volley events that have occurred in the last 140,000 years.
     As I pointed out in 1983, comet and asteroid impacts occur far too infrequently to explain such multiple cosmic dust incursion episodes (LaViolette, 1983a). Impacts by comets having a diameter of several kilometers, the size being suggested for the YDB event, occur about once every 30 million years unless triggered to enter by some other galactic event, and nearby energetic supernova, as mentioned earlier, occur less frequently than once in a million years. The superwave theory, though, offers an appropriate explanation for them since galactic explosions are a recurrent phenomenon. The cores of spiral galaxies are estimated to spend approximately 15% - 20% of their time in an active cosmic ray radiating mode. A spectral analysis study conducted by Liritzis and Grigori (1998) indicates recurrence intervals of 5 k, 12 k, 19 k, 25 k, and 40 k years in the Vostok Be-10 record. A study conducted by Omerbashich (2006) indicates a period as short as 3600 years may also be present. So if these Be-10 peaks reflect times of past superwave arrivals, it is clear that they arrive frequently enough to explain the observed cosmic dust events.
     Interestingly, one of the samples in which I found high levels of iridium correlates with the tail end of the 40 kyrs b2k cosmic ray event and another falls at the time of the 76 kyrs b2k event. The 40 kyrs b2k correspondence may be seen in figure 7 which compares the iridium deposition rates in these polar ice samples to the Be-10 data of Beer, et al.  Furthermore, one should not overlook the fact that the cosmic dust influx that occurred at the time of the megafaunal extinction also coincided with a Be-10 cosmic ray peak, as I note below. So one can make a good case for a connection between cosmic ray volley events and cosmic dust incursions.

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Figure 7. Upper profiles, oxygen isotope ratio and Be-10 concentration.  Lower profile, iridium deposition rate (data from LaViolette, 1985b, 2005a).

     Problem 17: Past cosmic dust deposition events last too long to be accounted for by comet impacts.  Another difficulty to ascribing a comet impact origin to these past ET dust peaks is that in some cases more than one iridium peak is found, suggesting that the ET material influx lasted several hundred years. For example, analysis of YDB sediments taken from Blackwater Draw, New Mexico and Lake Hind, Manitoba show two iridium peaks, one falling close to the AL/YD boundary and a second occurring about 200 years later; see figure 8. The peaks are separated by 4 cm of sediment at Blackwater and 17 cm of sediment at Lake Hind. The finding that the upper Ir peak at the Lake Hind site has a sediment date several hundred years younger than the peak below it gives reason to believe that the peaks are not contemporaneous. This evidence contradicts the claim made by Firestone et al. (2007c) that iridium was found only at the YD boundary and neither below or above it. If the extinction were due to a cometary explosion or impact, only one peak should have been formed, most of the dust being expected to settle out within a few years. Multiple peaks would require multiple impact events with the consequent problem that it is highly improbable that impacts would recur with such frequency. Multiple peaks, however, do not pose a problem for the superwave interpretation since a superwave would have pushed cosmic dust into the solar system over a period lasting hundreds of years.

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Figure 8. Iridium concentration in sediments from Lake Hind, Manitoba (top), and Blackwater Draw, New Mexico (bottom); after Firestone, et al. (2007c).
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     Additional evidence that cosmic dust was being deposited over an extended period of time is seen in the case of the 50.5 kyrs b2k tin dust event registered in Greenland ice. The dust in this sample was filtered from a 35 centimeter long ice core sample which represents an ice accumulation time span of at least 360 years. Thompson, who initially analyzed this sample, divided the ice core section into 17 consecutive samples each representing about two centimeters of core depth (~21 years) and used a Coulter counter to count the number of particles in each sample that were greater than 0.6 microns in diameter. He found that while the particle count varied from one increment to the next this variation for the most part did not exceed 100% of the mean number count; see figure 9. Only one sample had a count about three times the mean value, but this sample represented only about 15% of the particle count for all 17 samples totaled together.  This indicates that this tin-rich dust, which was later found to be mostly of extraterrestrial origin, was entering the Earth's atmosphere at a relatively constant but variable rate during this 360 year period. This negates the possibility that the dust originated from a cometary explosion or cometary impact event. For, if it had originated in this fashion, it should have remained airborne for no more than a few years before settling and hence should have formed a single dust band within a single increment of the 35 cm long section. It is reasonable to infer that the other ice core depths containing high Sn concentrations (discovered both in Thompson's study as well as in my own) also involved a relatively continual dust particle influx over periods of hundreds of years. In other words, what is evident from analysis of the 50.5 kyr b2k event may be typical of other tin influx events as well. So cometary impact explanations for those events seem unlikely.

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Figure 9. Particle count versus depth in Camp Century, Greenland ice core sample at a depth of 1230.5 meters dating from 50,500 years b2k. (after Thompson, 1977, p. 128)

     Another important point is that microspheres were relatively absent in the 50.5 kyr b2k dust sample. The tin-bearing dust particles are irregular in shape and have a flat, plate-like appearance. To maintain this shape during entry through the Earth's atmosphere without melting into microspheres indicates that they must have been entering at a low velocity and experienced essentially no heating or atmospheric ablation. So while microspheres discovered at the 12.9 kyr b2k boundary, as well as those found embedded in PaleoIndian artifacts, might point toward the occurrence of one or more comet explosions or impacts at that time, some other kind of mechanism must be put forth to explain the earlier dust events. They require a theory that explains how large quantities of dust manage to enter the solar system in particulate form. The superwave theory is one such theory.
     Some microtektites and cosmic microspheres could have a noncometary impact origin. Although Firestone and West make a good case for a comet explosion origin for the high concentration of microtektites and microspheres observed at the YD boundary, we might venture that melted particles of this sort discovered at the YD boundary may not all have originated from a comet explosion/impact.  Although spherules can be produced during atmospheric heating and ablation of impacting bodies such as meteors, comets, or asteroids, and also in the fireball of an exploding comet, as happened in 1908 at Tunguska, in reality, they are most commonly produced in space, not on Earth. They can be produced when interplanetary dust particles pass within Mercury's orbit and are melted by exposure to the Sun's radiation. Chondrules (microspheres) found in meteorites are also believed to be a component of cometary ice and would be released along with the more friable cosmic dust particles when cometary ice material is vaporized. Such vaporization may occur either when the comet is sufficiently heated by the Sun during its entry into the inner solar system, or in the case of a superwave event, when a comet passes through a high intensity region of Galactic cosmic ray radiation, as would exist in the heliopause sheath and surrounding shock front region during a superwave encounter. Evidence that cosmic spherules more commonly enter our atmosphere already in spherical form, as opposed to originating from the explosions or impacts of comets or asteroids, is discussed in my dissertation (LaViolette, 1983a, ch. 8); download chapter 8 excerpt.
     Also during this terminal Pleistocene period, when the zodiacal cloud is theorized to have contained high concentrations of cosmic dust, the Earth during this time would have accumulated a dense shroud of electrically charged dust particles forming a kind of meteoric veil (LaViolette, 1983a). Particles trapped in this veil, as well as dust particles present in the dust conjested interplanetary environment would have melted during exposure to the intense radiation of a major solar coronal mass ejection (CME). We know that solar flare activity was exceedingly high during the extinction event, as indicated from the rapid rise in C-14 at this boundary (figure 1) and from studies of solar flare tracks in lunar rocks. So it would have been quite possible that spherules were being produced by very intense CMEs. If the Earth's magnetopause had been impacted by a very large CME, temperatures in the Earth's storm-time radiation belts could have risen high enough to melt into spherules many of the dust particles residing in its metoeric veil. Furthermore the shock of the CME impact and the collapse of the geomagnetic field would have caused this spherule-bearing dust to become precipitously deposited on the Earth's surface, thereby creating a concentrated layer of ET bearing debris. So a solar coronal mass ejection event could mimic a comet impact.
      In discussing the YD boundary, one must also be aware that glacier waves, floods of glacial meltwater, issuing at that time in many places would have caused catastrophic sedimentary deposition at this boundary resulting in sediments being stratigraphically graded with the heavier higher density fraction concentrated at the bottom. Thus even though metallic dust particles and spherules may have had a history of gradual deposition over hundreds of years, during a meltwater flood the sediments would become stratified giving the false impression that their cosmic material fraction had been abruptly deposited.
     Helium-3 evidence also supports the superwave theory. Along a similar line, the helium-3 findings that the YDB group sites as evidence for their comet explosion theory need not necessarily originate from an incoming comet, at least not all the helium-3 reported at the YD boundary. For helium-3 is a common component of interplanetary dust particles. It becomes implanted in the particles during their exposure in space to the solar wind. So if there was an enhanced influx of cosmic dust at that time, one would expect to see elevated levels of helium-3 in soil sediments as well.
     Additional cosmochemical evidence that the tin particles are extraterrestrial. Further support of the extraterrestrial origin of the polar ice tin rich particles came in 1984. I had sent a piece of the tin-bearing polar ice dust to a laboratory in Australia for isotopic analysis. The sample had previously been stored in a safe place away from radiation sources. Three of the ten isotopes of this tin were found to contain isotopic anomalies, the abundance ratio for one of these, Sn-115, deviating by over three standard deviations from the terrestrial ratio. Hence these early results provided quite strong confirmation that the Sn was in fact of ET origin. Additional corroboration came in 1985 when the German cosmochemist Franz Rietmeijer (1985) announced finding tin oxide grains in interplanetary dust particles captured from the Earth's stratosphere. Although the Sn abundance was not anywhere near the abundance I had reported in one of my polar ice samples, it was nevertheless six times higher than concentrations typically found in carbonaceous chondrites.
     Claims that the tin arose from contamination were successfully rebutted. My discovery of volatile elements being found in polar ice dust in combination with high levels of ET indicators challenged accepted beliefs in the field of cosmochemistry. Previous studies on chemical composition of extraterrestrial material were derived primarily from analyses of meteorites. Hence any report of compositions different from standard meteorite abundances were looked upon with skepticism. In 1972, Hemenway, et al. reported finding unusually high concentrations of heavy metals in submicron sized dust particles collected from the stratosphere. But other than this, no researcher had previously reported the presence of high concentrations of such volatiles in cosmic dust.
     As a result, my findings encountered considerable resistance from certain conservative scientists in the cosmochemistry community. For example, in 1988, the French geochemist Claude Boutron published a paper in the journal Monthly Notices questioning the validity of my polar ice cosmic dust measurements (Boutron, 1988). He claimed that my samples must have been contaminated since I had reported that tin was present in many of them at substantially enhanced concentrations. I rebutted his paper that same year (LaViolette, 1988) giving detailed reasons why sample contamination was unlikely and arguing in support of an ET origin for the particles. So I am quite pleased to learn that high concentrations of tin have been discovered in YD boundary sediments alloyed with ET markers. For this gives even more reason to believe that I have been right in maintaining an ET origin for the tin found in polar ice.