Volcanism Theory
Some scientists believe that the ultimate cause of
the K-T extinction was a natural and gradual change that occurred
over several million years. Two main hypotheses exist today. These hypotheses
are tied together and could not have occurred without the other.
Volcanism: At the end of the
Cretaceous period there was increased volcanic activity. Over a period of
several million years, this increased volcanism could have created enough dust
and soot to block out sunlight; producing the climatic change. In India during
the Late Cretaceous, huge volcanic eruptions were spewing forth floods of lava
which can be seen today at the K-T boundary (these ruptures in the Earth's
surface are called the Deccan traps). The chemical composition of
the lava rocks in India shows that they originated in the Earth's mantle, which
is also relatively rich in iridium. This richness would explain the iridium
layer.
Plate
Tectonics: Major
changes in the organization of the continental plates (continental drift)
were occurring at the K-T boundary. The oceans were experiencing a regression;
they were receding from the land. A less mild climate would have been the
result, and this would have taken a long time.
