MadSci Network: Earth Sciences |
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.
Try the links in the MadSci Library for more information on Earth Sciences.