MadSci Network: Earth Sciences
Query:

Re: Is gravity the same now as it was when dinosaurs were around?

Date: Thu Nov 15 14:32:27 2001
Posted By: Thomas M. Greiner, Associate Professor of Anatomy / Physical Anthropology
Area of science: Earth Sciences
ID: 1005292074.Es
Message:

Is gravity the same now as it was when dinosaurs were around?

One of the most fundamental principles of scientific inquiry is that of 
Uniformitarianism. Stated in its simplest form, this principle requires 
that all physical laws and properties act the same today as they will in 
the future or in the past and in all parts of the universe. This is the 
only way that historical sciences (astronomy, geology, paleontology, etc.) 
can make predictions about how things operated in the past.

It is true that the Earth has gradually accumulated mass over its history 
through the accumulation of meteor strikes. However, this accumulation has 
been tiny compared to the total size of our planet. Therefore, it is 
extremely unlikely that the total gravitational pull of the Earth has 
changed in any meaningful way – especially during the history of life on 
earth. 

Recent evidence does suggest that there was a large meteor impact on Earth 
that roughly coincided with the extinction of the dinosaurs. However, that 
meteor would still have been relatively small compared to the total size 
of the planet. The mechanism for extinction associated with that impact 
usually has to do with the amounts of dust that would have been thrown up 
into the atmosphere, which would have blocked the sunlight and disrupted 
the ecosystem. To my knowledge, no one has suggested that this meteor 
changed Earth’s gravity, thereby making it harder for the large dinosaurs. 
You should remember that small dinosaurs became extinct as well.




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