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Commentaire de lecture : Gaïa : a new look at life on Earth

september 2003

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Year of publishing

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Minimum scientific background required
Gaia : a New Look at Life on Earth

James Lovelock


170 (paperback)

10 E


Science college undergraduate ?

NB : I read the book in French.

What characterizes life ? How do we kow that something is alive ? Is it the aptitude to reproduce itself, to eat, or more "technically" to reduce its internal entropy (to the detriment of external entropy, of course) that characterizes life ? Starting from these more or less "acceptable" definition of life, James Lovelock carries us into reflexions that are partly scientific and partly philosophic, to show how, under many aspects, our planet behaves exactely as a "global" living being.

In a living being we will find vital functions, that is able to maintain this state of life, that have the remarquable property of all having their embodied "intelligence", that is regulation mechanisms that allow them to remain at the good level. For example, all the molecules that circulate in the blood and are necessary to the good functionning of an organism - sugars, oxygen, CO2, hormones... - are regulated by mechanisms that prevent they get to widely apart from the "good" values ; the heart pulsations adapt so that the brain always gets the same oxygen no matter what the muscles deduct, etc....

Lovelock, as a "physician of the planet", exposes how the biosphere is regulated, just as our organism, by countless processes that also have a form of intelligence, and for which the adjustment capacity is perfectely dimensionned to the time scales involved. For example, for the past 3 or 4 billion years the average temperature on Earth has never been very different from what it is now, being at most a couple degrees (Celsius) over or under the present value, when the intensity of the sun radiation has increased by 30% or 40% meanwhile.

The "adaptation" mechanism of biosphere has been the diminution of the greenhouse effect, via a decrease of the atmospheric concentration of CO2, resulting from the photosynthesis of the first marine life (that consumed CO2 and rejected oxygen), as the intensity of solar radiation progressively increased. This process led to the indeed remarkable fact that the surface temperature of our planet did not vary much for several billion years.

It is again life that allows to maintain an oxygen share of 21% in the air (with no life on Earth free oxygen - which has a strong "lust" for combining with other elements - would vanish within a couple million years), a proportion which is sufficient to enable fast oxydation everywhere on earth (including fire), but just low enough so that a spontaneous fire does not devastate the whole vegetal cover on Earth (with a proportion of oxygen high enough, rain would not be able to stop forest fires).

Lovelock exposes also how, without regulation mechanisms, the proportion of salt in the ocean would have risen in several tenths million years to unbearable values for marine life (an excessive proportion of salt in sea water would induce an "explosion" of the membranes of cells, under osmotic pressure, because the salinity inside a cell is almost the same for terrestrial life and marine life), or how iodine, indispensable to all superior mammals, can be spread on the continents from the oceans via a gazeous cycle, or how tectonics allow, through volcanism, the long term recycling of elements that get trapped in the sediments at the bottom of the oceans...

Though he takes the precaution to state that it is not the case, one can of course wonder whether Lovelock doesn't see in an inhabited Earth the sign of some divine existence. One canno't prevent oneself to think, discovering this innumerable number of homeostatic functions, so wonderfully calibrated, with so marvelously complementary species, that the fact that such an ensemble advented under the mere effect of chance defies all laws of probabilities.

And, of course, the question that cannot miss to come up is : can we "break the machine" ? In this book, Lovelock's answer is clearly negative. For him, precisely because of its numerous regulation mechanisms, Earth will survive anything man might inflict to it. Humanity is above all a danger to itself, but not to biosphere in general, even if we can, without any doubt, profoundly modify the aspect of our planet. Superior life, the most emblematic for the defense of the environment (except us !), is paradoxally the least necessary to the whole equilibrium.

We should concentrate on protecting us from ourselves, nature can take care of itself, seems to say Lovelock in this book that skillfully avoids the double fault of catastrophism and mysticism (the latter not being easy given the matter). Thinking that Earth is in danger is meaningless : Earth is as it is, and it is possibly us who, at the time horizon of several centuries or millenia, are in danger as the dominant species living a comfortable life !


James LOVELOCK is physician and biologist. He is one of the rare representants of a kind difficult to qualify in the scientific world : a researcher without lab (or an independant researcher, now retired). He notably participated, with various qualifications, to various space programs of the NASA.


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