At the beginning of the Cambrian/Phanerozoic, some 600 million years ago, there was an explosion of different life forms, recorded in formations like the Burgess Shale in western Canada (pp. 110-112). Evidence points to several episodes of extreme glaciation (sometimes called "Snowball Earth") alternating with milder conditions (sometimes called "Greenhouse Earth") over an interval of less than 100 million years (650 to 570 million years ago) during which many of these new animal life forms evolved (p. 321). Can you suggest mechanisms by which this extreme variability in environmental conditions can be linked to the Cambrian explosion of life forms?

At the beginning of the Cambrian/Phanerozoic, some 600 million years ago, there was an explosion of different life forms, recorded in formations like the Burgess Shale in western Canada (pp. 110-112). Evidence points to several episodes of extreme glaciation (sometimes called “Snowball Earth”) alternating with milder conditions (sometimes called “Greenhouse Earth”) over an interval of less than 100 million years (650 to 570 million years ago) during which many of these new animal life forms evolved (p. 321). Can you suggest mechanisms by which this extreme variability in environmental conditions can be linked to the Cambrian explosion of life forms?