I wouldn’t have thought you could write 350 pages about “Air” without mentioning what gases make up Earth’s air and in what proportions, but William Logan has done it.
On the other hand, I’d have thought you could write 350 pages about “Air” without scatology, but William Logan hasn’t done that.
This is a very strange book in which we learn more about the untouristy places William Logan has visited than we do about trace gases in the atmosphere. When he does refer to the physical characteristics of air, he doesn’t always get them right; notably when he writes that the mass of the air is 500 trillion tons. That’s only one-eleventh of the accepted value.
Perhaps if he had spent less time on the vaporings of Maritain and Merton and more with reference books, he’d have gotten it right.
“Air” is not without its moments. Though he cannot be bothered to discuss the gaseous constituents of air, he is eloquent about the particles that the air supports, like fungus spores. He writes interestingly about learning to fly an airplane and sail in a hang glider; about weather; and about smells.
He also spends way more pages writing about the sonata form in western music than you’d expect —I’d have expected nothing — but what that has to do with air is not stated. He does point out that the sounds of music travel through air, but they travel also through water and steel.
The failure to discuss the constituents of air and their relative proportions is a very serious thing. Though Logan makes less of a fuss about climate change than I’d have expected, it is clear that he is among those who believe that the air’s share of carbon dioxide is titrated so delicately at three parts per 10,000 that it is ideal for humans, but that 4 parts per 10,000 would be a disaster.
The closest he gets to discussing proportions of gases comes in a discussion of oxygen levels (which, typically, he sets too low), which today are around 21%. He mentions they were very low before the evolution of photosynthesis, but there’s no hint that they seem later to have been very high — perhaps 50% above current levels.
You’d think that a discussion about why they dropped back and have settled, for quite a long time, at a lower level would have been part of a book about “Air.” But, again, you’d be wrong.
He mentions they were very low before the evolution of photosynthesis, but there’s no hint that they seem later to have been very high — perhaps 50% above current levels.
ReplyDeleteAt one time, there were insects absolutely gigantic by todays standards.
The theory being that due to their respiration, the upper limit of insect size was determined by O2 concentration: 30% during allowed dragonflys to have five foot wing spans.
As O2 concentration went down, so did insect size.
Until birds showed up -- now they are the limiting factor.
Anyway, insect size is a hint that O2 levels were at one time much higher than now.
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ReplyDeleteHere is the abstract from the source paper:
ReplyDeleteGiant insects, with wingspans as large as 70 cm, ruled the Carboniferous and Permian skies. Gigantism has been linked to hyperoxic conditions because oxygen concentration is a key physiological control on body size, particularly in groups like flying insects that have high metabolic oxygen demands. Here we show, using a dataset of more than 10,500 fossil insect wing lengths, that size tracked atmospheric oxygen concentrations only for the first 150 Myr of insect evolution. The data are best explained by a model relating maximum size to atmospheric environmental oxygen concentration (pO2) until the end of the Jurassic, and then at constant sizes, independent of oxygen fluctuations, during the Cretaceous and, at a smaller size, the Cenozoic. Maximum insect size decreased even as atmospheric pO2 rose in the Early Cretaceous following the evolution and radiation of early birds, particularly as birds acquired adaptations that allowed more agile flight. A further decrease in maximum size during the Cenozoic may relate to the evolution of bats, the Cretaceous mass extinction, or further specialization of flying birds. The decoupling of insect size and atmospheric pO2 coincident with the radiation of birds suggests that biotic interactions, such as predation and competition, superseded oxygen as the most important constraint on maximum body size of the largest insects.
Interesting.
I knew that. Logan discusses the reason insects are small today; since they don't have lungs, oxygen gets to each cell by diffusing through spiracles. Only so much can diffuse that way.
ReplyDeleteBut that was in a different section of the book. You'd think that in a book about air, that would have come up.
More interesting to me is the fluctuation of oxygen. Most of it is in rocks.
True.
ReplyDeleteBut, to me, it points to contingency. What if higher O2 levels lasted a bit longer?
Maybe bugs would be eating birds.
I wonder if life modulated oxygen, but then it's hard to explain how it got as high as it did. Presumably there's an upper limit at which multicellular life cannot tolerate free oxygen, just as there is a lower limit for carbon dioxide at which vascular plants cannot survive.
ReplyDeleteI think you are right about contingency; it does not appear there is some natural value to which free oxygen reverts.
I have seen suggestions that at some point fire starts to become a problem.
I cannot find it, but some entomologists on my FB feed sometimes post pictures of insects eating birds: praying mantises v. hummingbirds mostly.