There is no clear answer to this.
For a number of years, scientists focused on explanations for how the extinction might have occurred. Most theories focused on climate change, by volcanism, lowering sea level, and shifting continents. There were few other theories, some reasonable but others rather far-fetched. Anyway, most of these theories shared the common thought that dinosaurs had reached the end of their evolutionary life. Their extinction was seen as inevitable, the product of having evolved for too long. In most extinction scenarios, the dinosaurs were simply unable to cope with competition from mammals and the changing climate, and so they all went extinct.
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Thomas,Dingle commented on :
from what i know. a giant burning rock from space. although there is no proof of this
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