Earth has experienced a number of important periods in the course of life's origin and evolution. The late Proterozoic era (600-800 million years ago) was one of them. This period was also a point in Earth's history some call "Snowball Earth" when our planet was thought to have been completely covered with ice. This ice coating appeared and disappeared as the climate shifted back and forth - the whole process being modulated by atmospheric compostion and solar intensity.
A number of researchers feel that such conditions would stifle the ability of life on Earth-like planets to thrive - and that episodes such as this might actually hinder the development of complex (and eventually sentient) multicellular life forms.
Researchers at the University of Toronto and Texas A&M University have published data in Nature magazine which suggests that a belt of open water at the equator may have provided a refuge for animals while the rest of the planet was frozen over. These researchers suggest that the environmental challenge posed by these harsh conditions could explain the burst of evolutionary innovation that followed the Snowball Earth/Proterozoic Era - the so-called "Cambrian explosion".
While the data is of clear relevance to understanding the origin and evolution of life on Earth - and planets similar to Earth - there are also implications for worlds such as Europa that remain encased in a near-perpetual covering of ice - one which apparently breaks open in places for brief periods of time.
Related links
° Equatorial water may have provided means of survival for early life, press release, University of Toronto
° Neoproterozoic 'snowball Earth' simulations with a
coupled climate/ice-sheet model, Nature (Abstract - free registration required)
° A Refuge for Life on Snowball Earth, Science, [summary - can be viewed for free once registered. A subscription fee is required for full access.]
Background information
° Hot Jupiters and Rare Earths: Planets are common. Are we?, SpaceRef
° Paleoproterozoic snowball Earth: Extreme climatic and geochemical global change and its biological consequences, Proceedings of the National Academy of Science [Abstract - subscription fee required for full access]
° Snowball Earth and the Origin of Metazoa, Poster Presentation, First Astrobiology Science Conference, Paul F. Hoffman, Harvard University
° Snowball Earth, Scientific American, January 2000
° Snowball Fight, Nature
° Snowball Earth episode 2.4 billion years ago was hard on life, but good for modern industrial economy, research show, press release, Cal Tech
