  This monograph presents a study of the nature and origin of meteorites,
asteroids and comets; and of the consequences of encounters of these cosmic
objects with the Earth. The purpose of this monograph is mainly of divulgation
for non-specialists, even though we have not avoided some elementary technical
aspects and some own proposals: 1) Calculation of the evolution of an expanding
bubble originated by the explosion of a cosmic object that releases 50 Mt of
energy in the terrestrial atmosphere, at a height of 5 km from the ground. 2) A
new explanation of the white nights observed in Eurasia and of other phenomena
related to the Tunguska's explosion of 1908.
