When my world is rocked–when something I’ve “understood” all my adult life is stood suddenly on its head, or something important and there to know remains somehow invisible to me until all of a sudden, life is good. I’m still growing, learning, making a bit more sense of this place. In a moment of serendipity, a new reality appears–even at 62! I find the Internet has exposed me to many such “assumption shocks” over the past few years, and this kind of elder-discovery is a simple joy possible even with arthritis!
Now that was some buildup to tell you that I only yesterday discovered that 2.2 to 2.4 billion years ago, the Earth from space would have appeared like a great round powdered donut hole of ice. And there goes my belching volcano steamy-molten-jungley notions of the primitive planet as depicted in my 8th grade science book. I never heard of the Great Oxygen Catastrophe or “snowball Earth” periods and this for me is a startling discovery of a well known fact UNKNOWN to me all my life. Perhaps there are more?
Blame it on the Blue-Greens. The cyanobacteria are the culprits. And the heroes. (In truth, they are only part of the ancient ice-ages story if you dig deeper.) As these primitive photosynthesizing creatures expanded, the oxygen they produced drastically reduced the greenhouse gas, methane. BG’s are still very much still around. A species discovered only in 1986 accounts for more than half of the photosynthesis of the open ocean!) And the theory is, by endocytosis, blue-green algae evolved into land-plant chloroplasts.
There have been several “snowball” episodes (with varying caues) when ice covered earth from pole to pole. The last was between 700 to 600 million years ago. When it ended, the great Cambrian “explosion” of multicellular life (forms not easily related to any of our modern phyla) took place. Might be, biology today would not be anything like it is without these “hard knocks” that forced Life into all sorts of inventive solutions for survival during the extreme cold of the Snowball episodes.
See also: How Lowly Bacteria Froze Earth Solid