"How Early Earth Got Warm and Hospitable"
Space.com (June 3, 2010)
"Our planet might have kept warm in the super-ancient past when the sun was substantially dimmer than it is today because of a complex brew of global warming gases much like that now enveloping Saturn's moon Titan, scientists reveal.
"These new findings could also shed light on how the building blocks of life might have formed on Earth.
"When the sun was young, models suggest it was just 70 percent as bright as it is now. However, during the first two billion years or so of Earth's history, the surface of the planet was warm enough for glaciers to not form and early life to emerge...."
The article gives a pretty good overview of what's been discussed over the last several decades, about what Earth was like a really long time ago. Including the continuing story of ammonia in Earth's atmosphere. If you take ammonia and methane, and add electrical sparks: you get amino acids and other organic building blocks. Not life - but the parts you'd need for living organisms.
Just one problem - ultraviolet light destroys ammonia, and there would have been a whole lot of ultraviolet light back then.
Or, not. Something called fractal size distribution in the gasses we're pretty sure were in Earth's atmosphere should have blocked the shorter ultraviolet wavelengths, preserving ammonia, and let in longer visible light: keeping our planet warm.
Fascinating! If you're interested in that sort of thing.
If there's a lesson to be learned here: Change happens.
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