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Dinosaur Extinction
Dinosaurs inhabited the earth for over 165 million years.
Most dinosaur species lived and died out during this period, but
at the end of the Cretaceous period (65 million years ago),
all remaining dinosaur species (with the exception of birds which
had already evolved from dinosaurs) died out.
At the same time many other creatures also became extinct, including
all animals
weighing more than 55 pounds, and many marine (living in the sea) creatures too.
Scientists have proposed many different possible explanations (theories) of
why this mass extinction might have happened:
- Asteriod Impact Theory
An asteriod hit the earth. Apart from the immediate impact of fires and flooding, this would have
caused catastrophic changes in the environment because of the dust thrown up in to the air blocking out sunlight.
This is currently the most popular theory with scientists, because,
as
Luis and Walter Alvarez
pointed out,
iridium (which comes from asteroids) has been found all over the world at
the time the dinosaurs died out.
There is also a large
crater in Southern Mexico, which appears to be of the right age,
and could have been caused by the asteroid hitting the earth.
- Supernova Theory
A nearby star exploded as a supernova. This would have bathed the earth in deadly radiation.
- Volcanism Theory
Volcanos (known to be very active around this time) could have caused catastrophic changes in the environment.
- Climatic Change Theory
The earth's climate was changing at this time. Rapid changes in climate could have wiped out the dinosaurs.
- Mammals Ate Dinosaur Eggs Theory
Mammals ate the dinosaurs eggs - this used to be a popular theory -
but does not explain the extinction of many other species, especially
marine species.
Although many scientists now favor the asteroid impact theory,
it is not yet
actually certain that this is the reason why the dinosaurs died out. It is possible that
one of the other theories might be the correct one. It is also possible, that
there could have been several events which happened together, and between
them, killed all the dinosaurs.
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