Really cool science stuff from Astrobiology magazine. No, I am not making that up, and yes, I do check it our pretty often. My geekiness knows almost no bounds when it comes to space science.
Anywho, the point is that by researching Earth's past and how its atmosphere changed over its history, we'll better able to analyze whether or not extrasolar planets might have extrasolar life on them, once we get new sensing satellites like the European Darwin probe or NASA's Terrestrial Planet Finder into orbit that will be able to detect chemicals in far distant atmospheres.
"Astronomers Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics (CfA) and Wesley Traub of NASA's Jet Propulsion Laboratory and CfA, propose using Earth's atmospheric history to understand other planets. "Good planets are hard to find," said Kaltenegger. "Our work provides the signposts astronomers will look for when examining truly Earth-like worlds." Geologic records show that Earth's atmosphere has changed dramatically during the past 4.5 billion years, in part because of life forms developing on our planet. Mapping what gases comprised Earth's atmosphere during its history, Kaltenegger and Traub propose that by looking for similar atmospheric compositions on other worlds, scientists will be able to determine if that planet has life on it, and if so, that life's evolutionary stage. "
There have apparenlty been six different atmospheric epochs in the history of out planet, which was news to me. I knew it wasn't always the springtime fresh oxy-nitro (depending on what neighborhood you live in) we now have, but only was aware of the early methane phases before the introduction of the photosynthetic algae that produced our oxygen. What I find most interesting is that the nitrogen has apparently always been around in major concentrations.
Gratuitous link in the quote is to Dr. Lisa's Harvard webpage, showing yes, it is possible to be an female astrophysicist, AND also be really cute at the same time! Miracles never cease. Gotta wonder if she's married, but no woman smarter than me would ever be interested -- which has proven 100% correct over history. The only explanantion I can think of is that yes, she appears to be foreign, in this case Austrian. Sprechen Sie Deutsch, Fraulein?