ui wind speed
Figure 11.14 Variation of gas exchange rates in colonies of Macrotermes michaelseni. Gas exchange is assessed by the clearance rate of a propane tracer gas injected into the colony. A shallow slope of the plot of the tracer's log mole fraction (log mf) against time indicates slow exchange of gas, while a steep slope indicates rapid exchange. During periods of low wind speed, the tracer is cleared from the colony slowly. During periods of high wind speed, the clearance of tracer is approximately doubled.
a sufficiently high rate of ventilation. Far from shielding the colony from the disruptive influence of the wind, the M. michaelseni colony uses its mound to seek out and capture the energy in wind, appropriating it to power its ventilation. In short, the M. michaelseni mound is a fairly straightforward adaptive structure, no different in principle from the adaptive structures of the tuned singing burrow of mole crickets.
Similarly, the earth is affected by harmony and quiet music. Therefore, there is in the earth not only dumb, unintelligent humidity, but also an intelligent soul which begins to dance when the aspects pipe for it. —johannes kepi_er chapter twelve
In this, the final chapter of this book, we delve more deeply into the idea of the superorganism. We will explore a radical question: is the Earth a global superorganism that, like a colony of social insects, exhibits a coordinated global physiology, perhaps even a global homeostasis? One of the more remarkable ideas to come out of biology in the late twentieth century is that it does. In this view the Earth is portrayed as Gaia, a single, self-regulating living entity. What has come to be known as the "Gaia hypothesis" is the brainchild of James Lovelock, nominally an atmospheric chemist but, like all novel thinkers, one not so easily characterized. His idea was prompted originally by a practical question put to him by NASA: how do we decide whether or not a planet supports life? Lovelock's answer to this question was simple and obvious: look for evidence that the chemistry of a planet is held persistently out of thermodynamic equilibrium.
This answer did not endear Lovelock to NASA, because it meant that the answer could be determined from observations that could be made from Earth. This did not help NASA justify sending expensive spacecraft to Mars, and so at that point the mind of the bureaucratic beast lost interest. Lovelock's idea did not die, though, and Gaia has grown into what its proponents say is a comprehensive new theory of Earth biology, one which unifies previously disparate fields of scientific inquiry, like geology, ecology, and the life sciences. It has also resurrected a holistic view of nature that has largely been eclipsed by the triumphant reductionism that has dominated science throughout the late twentieth century.
In essence, Gaia is the superorganism writ large, and for reasons both good and bad it has been a controversial idea. I don't intend to use this chapter as a venue to air the various arguments pro and con. Rather, I wish to consider Gaia in light of the theme of this book: is there a global physiology that is mediated by structural modification of the environment, of which animal-built structures are an example? If you have been persuaded up to now that there is indeed physiology that extends beyond the organism, then you should be willing to entertain the idea that this external physiology could extend to large-scale systems, like communities, ecosystems, perhaps even the biosphere itself. Of course, it is a long reach from a termite mound to Gaia, but I will try to bridge the gap anyway.
The "Physiology" of Global Climate
To start, let us examine one of Gaia's claims—that the biota of the Earth regulates the Earth's climate. One obvious objection would be that the biota—all the flora and fauna collectively—is fairly weak in comparison with other forces that drive climate. Recall the discussion in Chapter 2: only a tiny fraction of the energy streaming into the Earth's atmosphere is captured by green plants for powering the ATP energy economy that all life depends upon. Far more energy is available in the physical energy stream to drive climate. How can the comparatively minuscule engine of the Earth's biota regulate such a powerful force?
It may not have to. Climate may in fact be rather delicately poised and susceptible to small biasing forces, just as a finely balanced beam might be tipped by the movement of a flea. For the past million years or so, climate has shifted between cold periods, called ice ages, and warmer periods, called interglacials, once every 100,000 years or so, almost as if it were being switched between two relatively stable states. This cycle is nicely illustrated by climate records for the past 35,000 years or so (Fig. 12.1), which encompass the latter part of the last ice age and the climb into the
Air temperature (oC) 0
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.