Why Did the Dinosaurs Die Out?

Name ______________________
Date ______________
Why Did the Dinosaurs Die Out?
By Sharon Fabian
Why did all of the remaining dinosaurs die out suddenly at the end of the Cretaceous period? There is a
short answer and a long answer to this question.
Here is the short answer. No one knows for sure.
Here is the long answer. There are a number of theories. Some are scientific, and some are ridiculous.
Most scientists believe in one or two main ones, but no one knows for sure.
The reason no one knows for sure is because the whole thing happened about 65 million years ago. No
one was around to see or hear what was going on back then, and no one was around to keep records.
What we do know comes mainly from fossil records. Scientists study the fossils themselves, and they
study the rock in which the fossils are found. Fossil records haven't given us definite proof for any one
theory. This is because there are some problems with fossil records. For one thing, most fossil evidence of
dinosaurs has been found in North America. We don't know as much about dinosaur activity on other parts
of the earth. Another problem is that it is very hard to date fossils. Dating fossils means determining how
old they are.
One really interesting thing about the big dinosaur question is that scientists from many different fields
are working to solve the problem. Astronomers, physicists, geologists, paleontologists, ecologists,
chemists, geologists and others are all gathering evidence, experimenting, and researching to try to solve
the puzzle.
The most popular theory is called the Alvarez Hypothesis. This hypothesis says that, 65 million years
ago, a big asteroid hit the earth. This asteroid crash scattered dust high up into the atmosphere. It blocked
much of the sunlight and caused the earth to become cooler. The crash also started huge fires, high winds,
and violent storms that killed some of the dinosaurs. The lack of sunlight and warmth caused many plants
to die. This shortage of plants for food caused the rest of the dinosaurs to die out.
The second most popular theory says that activity on the earth itself caused the extinction. As the
supercontinent of Pangaea was breaking up, movement of the earth's giant land plates caused volcanoes
to erupt and the climate to change. These changes affected the earth's atmosphere and temperature, and
the dinosaurs died out from the cold or from lack of plants to eat.
Other theories suggest that dinosaurs became so big that they couldn't move, or that there were too
many dinosaurs and they ate up all of the food.
There is a theory that, as the continents shifted, dinosaurs spread germs from one herd to another.
According to this theory, dinosaurs died out from sickness.
Another idea is that mammals ate up all of the dinosaurs' eggs.
Some people have suggested that an unusually bright star, a supernova, killed the dinosaurs with its
deadly radiation.
There is even a theory that dinosaurs died out from hay fever. Flowering plants began to grow during
the late Cretaceous Period. Maybe dinosaurs were very allergic to flowers.
So, what did cause the dinosaurs to die out? No one knows for sure.
1. After the end of the Cretaceous Period,
there were _____.
Only old dinosaurs
No more dinosaurs
Half as many dinosaurs as before
Only two types of dinosaurs
2. The Cretaceous Period ended _____.
65 million years ago
100 million years ago
165 million years ago
200 million years ago
3. We don't know for sure why the dinosaurs 4. The two most popular theories both say
died out because _____.
that dinosaurs died out because of changes
There were no people alive back
in the earth's _____.
then to see what was going on
Atmosphere and temperature
There was no one to keep records
Volcanoes and clouds
Fossil evidence doesn't give us all of
Fossils and rocks
the answers
Dinosaurs and mammals
All of the above
5. According the Alvarez Hypothesis, the
changes were caused by a(n) _____.
Giant dinosaur
6. Some scientists think that shifting of the
earth's _____ caused the changes.
7. All of the following are possible theories 8. There is no scientific evidence for any of
mentioned in this article, except _____.
the theories. Real scientists don't bother
Hay fever
studying about dinosaurs.
Attack of giant mosquitoes
Shifting plates
An asteroid hit