From James Davies, Open University
The proposed cyclic behaviours of the black hole at the centre of the Milky Way (New Scientist, Science, 22 October) suggests another explanation for the mass extinctions at the end of the Permian and Cretaceous periods. The Alvarez meteorite and catastrophic lava flow theories cannot explain the long-term decline of the dinosaurs before the final extinction.
Suppose that the black hole flares for some 1 million years every 200 million years or so: the resulting X-rays would certainly have a longterm effect on life on this planet. The creatures best able to survive it are those with a short lifespan (to avoid dying of cancer), those living underground (such as small mammals) and fish (which are shielded by the ocean).
This is rather difficult to prove. But the mutations caused by the X-rays would increase the speed of evolution of the survivors, so a change of this nature might be detectable.
This cannot explain such things as the soot and iridium layer, which suggest that a meteorite or lava flow dealt the final blow.
Advertisement
