One of the most
popular explanations for this catastrophe is that an asteroid or
comet stuck this earth. The collision is assumed to have caused
huge clouds of dust or sulphuric acid, which blocked sunlight
and which led to global cooling. There must have been a very
drastic change in the climate, which permitted only a few living
organisms to survive.
There is a very
thin layer of a rock with a rare property- the presence of the
element iridium. Iridium is very rare on earth but not in
asteroids or meteorites.
The other famous
theory is that of "Mass extinction". The scientists
believe that a million years ago as the global climate changed
rapidly it caused the theory of mass extinction.
believe that there must have been a variation in earth’s
magnetic field or due to volcanoes.
remains a mystery.