However, organisms and ecosystems, as far as it can be determined by the fossil record, do not appear to have undergone the significant change that would be expected by a mass extinction. With the advent of more precise dating, a phytoplankton extinction event which had been associated with snowball Earth was shown to precede glaciations by 16 million years. Even if life were to cling on in all the ecological refuges listed above, a whole-Earth glaciation would result in a biota with a noticeably different diversity and composition. This change in diversity and composition has not yet been observed—in fact, the organisms which should be most susceptible to climatic variation emerge unscathed from the snowball Earth. One rebuttal to this is the fact that in many of these places where an argument is made against a mass extinction caused by snowball earth, the Cryogenian fossil record is extraordinarily impoverished.