02 June 2009
From Denny: It seems like every few years scientists decide the Earth is really an older planet and, oh, by the way, they think the sun will exist for a few million or so years longer. Not to worry, folks, we will still have a home for mankind for a little while longer! :) Here's the latest from Wired.com's Wired Science blog.
"The Earth could be habitable for another 2.3 billion years, extending previous estimates of life’s horizon by more than 1 billion years.
King Fai Li and his colleagues at Caltech hypothesize that Earth’s atmospheric pressure has always varied, and that it could fall in the distant future, keeping Earth from frying for far longer than previous research had shown.
If the new idea proves correct and can be extended to other planets with biospheres, it could increase the chances that earthly civilization finds extraterrestrial life by doubling the percentage of time that planets could be inhabited.
“[T]he Earth will be identifiable as an inhabited planet for nearly half the total lifetime of the Sun, an important point to consider in the search for life on extrasolar planets,” the authors write in the Proceedings of the National Academy of Sciences.
Over the next hundreds of millions of years, the sun will continue to get brighter until eventually, Earth becomes too hot to inhabit. Previous calculations had pegged that time at about a billion years from now, but the new paper argues that earlier models had neglected the role of atmospheric pressure in regulating the temperature of the planet on astronomical time scales.
Atmospheric pressure is a key variable in the overall greenhouse-gas effect because it determines how much infrared radiation greenhouse gases absorb. Higher pressures mean more absorption and consequently, more heat. Lower pressures have the opposite effect.
Life itself would be the mechanism for these temperature changes. By “fixing” nitrogen, pulling it out of the air and eventually into the Earth’s deep ocean, microbes could be making the atmosphere lighter one atom at a time.
“I am glad that Li and colleagues have raised the issue of how overall variation in atmospheric pressure may have affected past and may affect future climate,” ecologist Ken Caldeira of Stanford University said in an e-mail. “This could be relevant for understanding climate change on the billion-year time scale.”"
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