The abundance variations of iridium and other related elements in the peat samples from a drilling hole of the Tunguska explosion epicenter were studied by neutron activation analysis. We found the striking anomaly of iridium abundance at the 1908 explosion layer and its overlying strata

whose maximum reaches over five times higher than the background value. On the basis of the elemental correlation of Ir with Ni and Co and in combination with the information of hydrogen and carbonisotopic excursions

a hypothesis that a comet entering the earth orbit might causethis modern explosion event was deduced.