Did ice ages trigger the evolution of animals?

Science : Twice in Earth’s past, the planet was covered almost completely in ice. Those episodes coincide with the rise of oxygen-breathing animals. Coincidence? Not according to a paper in today’s Nature. Noah Planavsky of Woods Hole Oceanographic Institution in Massachusetts and his colleagues report the results of measuring the phosphorous content of iron-rich minerals that formed long ago in the oceans. The P content of the rocks reflects the P content of the surrounding seawater at the time of their formation. Ordinarily, iron-rich rocks form with roughly the same P content, but Planavsky and his team noticed two strong exceptions: the two periods just after the extensive glaciations. In Planavsky’s scenario, the retreating glaciers ground up rock, which was flushed into the sea, raising both the P content of contemporaneously formed rocks and, through P’s fertilizing effect, the oxygen output of marine algae. Elevated levels of atmospheric O could have given a kickstart to the evolution of animals.