Thomas' Plant-Related Blog

On plant science. Mostly.

Does Gaia let the pressure down?

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From Nature News: Atmospheric pressure may have changed to alter the earth’s temperature as the sun cooled down.

As the piece acknowledges, this has links to Gaia, a rather radical hypothesis that life modifies its environment to keep it suitable for life. This has been turned into some rather unscientific metaphors about the Earth being a ‘living organism’, but we’ll ignore those. The actual idea, that life has a stabilising effect on the world it’s in, can reasonably be viewed as a scientific hypothesis, in my opinion.

When the earth first formed, some four billion years ago, the sun gave out rather less heat than it did now. It’s been getting more powerful very slowly since then, and it’ll probably carry on. But if there was less heat from the sun, how could it have been warm enough for life to get started?

As an aside, the question of what temperatures life can endure is interesting itself. Modern life can survive everywhere from scorching deserts to frozen snow, but as far as we know, they all need liquid water for at least part of their life, so the limits are no broader than roughly 0-100°C.

The study says that Earth’s atmosphere was originally much denser than it is now, helping to trap more heat. Over time, life has fixed nitrogen from the atmosphere (for example, plants such as peas and beans use bacteria in their roots to fix nitrogen), and it has been taken into the earth by tectonic movements. Gaia’s hand on the thermostat?

The key is regulation: it’s unlikely that the total amount of life would just happen to suck up nitrogen at the rate needed to keep temperature more or less constant. Gaia is all about negative feedbacks: systems which automatically correct themselves. So, if Gaia was involved, a warmer planet would have triggered faster uptake of nitrogen, while a cool environment would have led to slower nitrogen fixing, to keep the atmosphere thick. Plants would, perhaps, grow faster in the warm (leading to more fixation), but would soil bacteria also speed up, releasing more of the nitrogen back to the atmosphere?

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Written by Thomas Kluyver

17 November, 2009 at 2:15 pm

Posted in Uncategorized

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