THE MICROSTRUCTURE OF TERRESTRIAL CATASTROPHISM

The theory of evolution involving episodic terrestrial catastrophism predicts that the Oort cloud is disturbed by close encounters with massive nebulae. Each disturbance generates bombardment pulses of a few million years duration, the pulse frequencies being determined by the Sun's passage through the spiral arms and central plane of the Galaxy where nebulae concentrate. The structure within a pulse is shown here to be dominated by a series of 'spikes' of 01-0.1 Myr duration separated by .1-1. 0 Myr, each caused by the arrival in circumterrestrial space of the largest comets followed by their disintegration into short-lived Apollo asteroids. The iridium-bearing layers at the Cretaceous-Tertiary and Eocene-Oligocene boundaries are probably not simple impact signatures therefore but are evidence of passages through the complex and dusty interplanetary environment temporarily created by these disintegrations. Evidence is presented that a bombardment pulse was induced 3-5 Myr ago and that a 'spike' in the form of debris from a Chiron-like progenitor of Encke's comet has dominated the terrestrial environment for the last 0.02 Myr: a devolatilized core of substantial dimensions (10-30 km) may still exist. Among the predicted consequences are 14C modulations, climatic variations including the last major glaciation and observable zodiacal light phenomena. The fact that a single dominant body is involved also provides a natural explanation for the common Ni/Ir ratio now observed in Tunguska spherules (1908 AD) and cosmic dust concentrations in Late Pleistocene polar ice (16000-12000Bc). The non-Solar System proportions of such elements as Sn, Sb and Ag, moreover, are consistent with the expected interstellar origin of this particular progenitor comet. © Royal Astronomical Society • Provided by the NASA Astrophysics Data System.