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.
4 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.
5 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.
6 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.
7 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.
8 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.
9 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.
10 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.
11 Another idea is that mammals ate up all of the dinosaurs' eggs.
12 Some people have suggested that an unusually bright star, a supernova, killed the dinosaurs with its deadly radiation.
13 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.
14 So, what did cause the dinosaurs to die out? No one knows for sure.
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Name Date Period
Why Did the Dinosaurs Die Out?
1. / After the end of the Cretaceous Period, there were _____.Only two types of dinosaurs
Half as many dinosaurs as before
No more dinosaurs
Only old dinosaurs
/ 2. / The Cretaceous Period ended _____.
165 million years ago
65 million years ago
100 million years ago
200 million years ago
3. / We don't know for sure why the dinosaurs died out because _____.
There were no people alive back then to see what was going on
There was no one to keep records
Fossil evidence doesn't give us all of the answers
All of the above
/ 4. / The two most popular theories both say that dinosaurs died out because of changes in the earth's _____.
Fossils and rocks
Dinosaurs and mammals
Atmosphere and temperature
Volcanoes and clouds
5. / According the Alvarez Hypothesis, the changes were caused by a(n) _____.
Giant dinosaur
Asteroid
Volcano
Storm
/ 6. / Some scientists think that shifting of the earth's _____ caused the changes.
Plates
Countries
Oceans
Mountains
7. / All of the following are possible theories mentioned in this article, except _____.
Shifting plates
Hay fever
Attack of giant mosquitoes
An asteroid hit
/ 8. / There is no scientific evidence for any of the theories. Real scientists don't bother studying about dinosaurs.
False
True
Why Did the Dinosaurs Die Out? - Answer Key
1 No more dinosaurs
2 65 million years ago
3 All of the above
4 Atmosphere and temperature
5 Asteroid
6 Plates
7 Attack of giant mosquitoes
8 False