Snowball Earth: Two phases that stimulated evolution.

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Life After 'Snowball Earth': New Fossils Suggest Rapid Recovery of Life After Global Freeze

ScienceDaily (June 16, 2011) — The first organisms to emerge after an ancient worldwide glaciation likely evolved hardy survival skills, arming themselves with tough exteriors to weather a frozen climate.

Researchers at MIT, Harvard University and Smith College have discovered hundreds of microscopic fossils in rocks dating back nearly 710 million years, around the time when the planet emerged from a global glaciation, or "Snowball Earth," event. The fossils are remnants of tiny, amoeba-like organisms that likely survived the harsh post-glacial environment by building armor and reaching out with microscopic "feet" to grab minerals from the environment, cobbling particles together to make protective shells...

I must confess to be very interested in the "Snowball Earth" period as it appears to be such a crucial point in the evolution of complex life on Earth. If one takes the whole of the Earth's 4.5 billion year existence for 3 billion of those years the Earth was overtly ruled by micro-organisms. It still is ruled by micro-organisms, just covertly, in the form of cooperative colonies i.e. multi-cellular organisms. What made micro-organisms cooperative and what was it about the 'snowball earth' period that appears to have caused/facilitated this evolutionary development?