When All of the Oceans Were Frozen

Science is the most fun when it makes things simple. And it is at the best when we find a theory that makes many previously-unrelated observations fit together like a puzzle, and which then leads to new predictions and discoveries. During the midto late 1960s, Plate-Tectonics did this in grand style for most of the Earth sciences, allowing an entire host of observations from paleontology to petrology to be united within one simple, all-encompassing framework. Although major conceptual advances of this sort are rare, we can still have a lot of fun exploring many aspects of Earth history, and testing novel ideas for unifying and understanding diverse sets of observations. My Snowball Earth theory [1] was an attempt to do this for mysterious glacial deposits in late Precambrian time (between about 730 and 590 million years ago), which were poorly understood, yet clearly preceded the most important diversification of life known on this planet, the Cambrian Explosion. In this brief commentary, I will review the development of this theory, and give my opinion on some of the current issues related to it that are now being debated vigorously.