But IF (as is thought) that the meteor OR comet exploded 5 miles above the earth and the whole event was caused by the shockwave of said meteor or comet, surely there would not be very much if ANY material left to find to prove either theory .
As seems to be the case cuz the arguement for both still continue today.
That is what keeps it interesting. You see, evidence of past major asteroidal and cometary impacts left behind sediment rich in the element iridium in our crustal layers, something naturaly extremely rare on Earth, but rich (in relative standards) in asteroids -> comets from the formation of the early Solar System. I don't know myself how volatile an element iridium is, but the evidence we see is buried in sedimentary rock, so what
could have been left on the surface at Tunguska
could well have dissipated by now.
Iridium found as a result of a comet impact (like that found to date to around 63 million years ago in the Earth's crust) is also only a recently discovered phenomenon, so I don't think it was high on the list of priorities when the first expedition to Tunguska occured over 10 years later in the mid 1920's.
Seanie.
  