The timing of the great extinctions Over geological time, there are five great extinctions. The period and time of these great extinctions are Period | Time (Million years ago) | Ordovician | 440 | Devonian | 370 | Permian | 252 | Triassic | 200 | Cretaceous | 65 |
Of the five great extinctions, The first, the third and the fifth have the highest extinction rates. See Figure 18 of Benton (2003) for details. The third extinction, the Permian great extinction ended the Paleozoic era.The fifth extinction, the Cretaceous great extinction ended the Mesozoic era.The time difference between the first to the third is about 188 million year. The time difference between the third to the fifth is about 187 million year. Note that the time differences between the first to the third and the third to the fifth are almost identical. Is this a coincidence? Or is there a connection between these extinctions to some periodic celestial movements?
Imagine there is some periodic encounters between the solar system (or the earth) and some meteoroid or asteroid ring with a period of about 188 millions. This could explain the occurences of the first, third and fifth great extinctions.The end of Cretaceous extinction could be caused by a huge asteroid and some smaller ones. The impacts of smaller asteroids are difficult to trace. The evidences of impacts generated by earlier asteroids could be difficult to trace as well.Instead we might look for direct evidence in celestial movements.
References
Benton, M.J., 2003. When life nearly died: the greatest mass extinction of all time. Thames & Hudson. |
