Problem 6: Hot supernova gases can't condense into iron particles in just 7000 years. I also agree with the blog correspondent named Günther who questions whether supernovae can produce iron-rich particles within the 7000 years time that it would take for these particles to reach the solar system after crossing a distance of 250 light years at 10,000 km/s. He notes:

   "Investigations performed by radioastronomic and astrophysical research over decades has revealed that if a supernovae explodes, it does this at extremely high temperatures (many millions of kelvin), and that it casts ejectae into space at speeds of up to 40000 km/s. At such a temperature, these ejectae are not solid matter, but are a hot plasma which is at a high pressure. Driven by this pressure the cloud of plasma travels out into space, where it expands and reduces its pressure. As it expands, it collides with the cooler interstellar matter that surrounds location of the supernova.
   This collision creates a hot shock front that moves through the interstellar matter, collecting that matter and filling up its former location with the matter from the supernova. According to these scientists, it takes hundreds of thousands of years until the ongoing collision with the interstellar matter has reduced the speed of expansion to a rate equal to that of the average speed of interstellar matter. Then the shock front dies away and cools down, and the matter of the ejectae is able to cool down to some thousand kelvin.
Only that cool, the matter is able to do the transition from its plasma state to form atoms. At that state, the matter ejected from the supernova may fill a sphere with a radius of many light years. That is a huge volume, and the density of the matter within this volume is extremely low.
   It takes another hundred of thousands of years until micron-sized dust particles may start to grow in this thin matter, and it takes further millions of years for these particles to create larger particles, which break up again, as they collide with each other in the long course of time. It takes extremely long time to form bodies from an environment which contains only a few atoms per cubic inch. Thus, the estimation of 7000 years for this process, as proposed by the researchers, is far too low. The matter ejected from a supernova explosion requires much more time to cool down and form particles, if it will form any particles at all. I never read a report on or heard of a comet that may have grown in a short time. It very much looks like physics simply do not allow this."
Günther: http://www.bautforum.com/archive/index.php/t-1180.html%3C/t-33032.html

     Problem 7: Insufficient supernova buckshot. From the pictures that Firestone, West, and Warwick-Smith show in their book, we learn that these iron grains ranged from half to two millimeters in size and were spaced on the average roughly 5 centimeters from one another. This implies a particle mass flux of approximately 1 to 5 milligrams per square centimeter. They found this pitting in one tusk out of 70. So let us reduce our mass flux estimate by two orders of magnitude. This gives a flux of about 10 micrograms per square centimeter. Clearly, this is far greater than could be supplied from the 41 kyrs b2k supernova. For if one percent of the supernova progenitor star's mass were composed of ferrous metals that later condensed to form this shower of pellets, this amounts to only 0.2 nanograms per cm² if uniformly spread over a 250 light year sphere. So, to get the kind of tusk peppering they observed they would have needed one hundred thousand times more matter than it was possible to get out of their supernova explosion. Again, they could assume that Earth had the misfortune of being hit by a high density cluster of this supernova buckshot, but this proportionately reduces the likelihood that this would have happened.
     Problem 8: Such high speeds not needed for tusk pitting. A speed of 10,000 km/s is far higher than needed to explain the hypervelocity impact craters found in the mammoth tusks. While experiments showed that the tusks could not be penetrated by pellets fired from a shotgun at 1000 kilometers per hour (i.e., at 0.3 kilometers/second), speeds an order of magnitude greater such as a few kilometers per second, typical of micrometeorite velocities, should have been sufficient. This seems quite reasonable considering that Topping (1999) determined that speeds of just 340 meters per second were sufficient to create pits in cherts. It is apparent that speeds 10,000 fold higher, of the sort proposed by Firestone and West, are entirely uncalled for. They seem to have chosen this 3% c relativistic velocity primarily as a desperate attempt to make their supernova model account for the C-14 peaks present in the Icelandic marine record.
     Problem 9: Supernova remnant observations do not support their hypervelocity speed model. The Firestone-West supernova remnant expansion scenario has the problem that 7000 year old supernova remnants are not observed to have such high ejecta speeds (10⁴ km/s). Such speeds are over two orders of magnitude too high for remnants of this age. Neither would the ejecta in a 28,000 year old remnant (41,000 years BP minus 13,000 years BP) be expected to have speeds as high as 2100 - 2700 km/s, as required by the Firestone-West theory. Delaney and Rudnick (2003) have simulated the expansion of Cassiopeia A, a 335 year old supernova remnant that is currently 11 light years in diameter and that was formed by a relatively energetic supernova explosion. Its initial expansion rate is projected to have been on the order of 15,000 km/s which at its present age of 335 years has dropped to about 4000 to 9000 km/s. They project that at an age of 1000 years Cas A's expansion rate will have dropped to about 2000 km/s. Projecting this trend into the future one would expect the expansion rate to continue to drop reaching only some tens of kilometers per second by the time it reaches an age of 7000 years. So a similarly low speed would be expected for a 7000 year old remnant in the Sun's vicinity.
     If Firestone and West had a good reason to assume a relativistic remnant expansion velocity at the time of terrestrial impact, they should have proposed a much more compact and much younger supernova remnant, say one positioned 60 times closer to Earth (4 light years away), placing it as close as the nearest star Alpha Centauri. Although an explosion this close to Earth would statistically have been a million times less probable, it would be entirely permissible for them to postulate high velocity supernova ejecta coming from a supernova remnant shell as compact and young as this. However, a 10,000 km/s blast would then take only 100 years to reach Earth and if this was followed by their proposed secondary 2700 km/s blast, this second onslaught would arrive only 300 years later. So their hopes of simultaneously accounting for three C-14 anomalies in the geologic record, at 41 kyrs BP, 34 kyrs BP, and 13 kyrs BP would be entirely dashed.
     Problem 10: No evidence of the alleged hypervelocity supernova shell. There is also the concern that Firestone and West present no evidence for the current location in the heavens of their alleged supernova remnant shell. If ionized supernova remnant material were traveling outward at thousands of kilometers per second, this redshift signature would have been easily detected and should have been known to astronomers. By now, the forefront of the remnant, if it continued outward at 10,000 km/s should have produced a shell diameter of some 350 light years and its inner surface should be positioned about 80 light years away. But there have been no reports of such. By comparison the North Polar Spur remnant, which the superwave theory assumes as the source of the cometary material currently surrounding the solar system, is a remnant whose existence is very well documented.
     Firestone, West, and Warwick-Smith (2006) suggest that the Geminga supernova which they propose for this 41,000 year old event swept out a low density pocket in the interstellar medium and they identify this with the the Local Bubble that surrounds the Sun. As mentioned earlier under Problem 2, sweeping out such a cavity would have substantially decelerated their remnant, raising the problem of delaying the remnant's arrival. It seems more plausible that the Sun itself created this cavity, the bubble being the aftermath of a high velocity solar wind that once blew with extreme ferocity at the close of the last ice age. For as we know from the lunar rock evidence of Zook, et al. (1977), the Sun's flaring activity was extremely high at that time. A highly energetic solar wind, strong enough to clear out a low density region around the Sun would explain why this bubble has its long axis aligned with the Sun's poles. For the solar wind moves outward at its highest velocity at the Sun's poles, being least impeded there by the solar magnetic field.