“The 8% level is the minimum required for the existence of large-bodied animals that lack digestive tracts and internal organs (the Avalon animals, e.g. sponges and jellyfish). The 10% level is the minimum required for animals with complex internal organs (the Cambrian animals). One of the great marvels of life history is that the Avalon and Cambrian animals representing several Avalon phyla and 30+ Cambrian phyla appeared in what may be considered a geologic 'instant' after each of the oxygen levels was attained.”