Reply to Comment on Snowball Earth



I welcome the signs of a dialectical engagement in the evaluation of the Snowball Earth hypothesis.

Paul Hoffman proposes that on the basis of Kirschvink's two-page chapter [Kirschvink, 1992], there are five main pillars in support of the Snowball Earth hypothesis. I cannot agree that the five pillars mentioned by Hoffman can be discerned in Kirschvink's original piece. A pillar must be a line of argument and supporting data that the protagonist views as being strongly and uniquely supportive of the hypothesis. Using the architectural metaphor, a pillar is solid, supportive, and unchanging. There are no such pillars in Kirschvink's article. He admits that his hypothesis is “speculative” (p. 51) or, more precisely, involves an alternate “equally speculative mechanism” to that of high obliquity to explain apparently low-latitude glaciation. Kirschvink suggested that there were several implications of his global snowball model, but no compelling evidence was presented.