Riley explained the 3 Cambrian Explosions as due to oxygen. What does Stephen Jay Gould say?

"Such delays speak strongly against general progress as the major theme of life's history, EVEN IF they can be PLAUSIBLY explained by lack of sufficient atmospheric oxygen for most of Precambrian time or by failure of unicellular life to achieve some structural threshold acting as a prerequisite to multicellularity. " [ my empahsis, showing that this is not a scientific argument as Riley says it is ] cbtbanking.com