We interviewed Toby Tyrrell about his new book “On Gaia” last week. This week, we’re proud to link to this article in which he details some of the research that led him to view the Gaia Hypothesis with a critical eye:
Nitrogen is exceptionally abundant in the environment, it makes up 78 per cent of air, as dinitrogen (N2). N2 is also much more plentiful in seawater than other dissolved forms of nitrogen. The problem is that only organisms possessing the enzyme nitrogenase (organisms known as nitrogen-fixers) can actually use N2, and there aren’t very many of them. This is obviously a less than ideal arrangement for most living things. It is also unnecessary. Nitrogen starvation wouldn’t happen if just a small fraction of the nitrogen locked up in N2 was available in other forms that can be used by all organisms; yet biological processes taking place in the sea keep nearly all that nitrogen as N2. If you think about what is best for life on Earth and what that life can theoretically accomplish, nitrogen starvation is wholly preventable.
This realisation led me to wonder what other aspects of the Earth environment might be less than perfect for life. What about temperature? We know that ice forming inside cells causes them to burst and that icy landscapes, although exquisite to the eye, are relatively devoid of life. We can also see that ice ages – the predominant climate state of the last few million years – are rather unfortunate for life as a whole. Much more land was covered by ice sheets, permafrost and tundra, all biologically impoverished habitats, during the ice ages, while the area of productive shelf seas was only about a quarter of what it is today. Global surveys of fossil pollen, leaves and other plant remains clearly show that vegetation and soil carbon more than doubled when the last ice age came to an end, primarily due to a great increase in the area covered by forests.
Although the cycle of ice ages and interglacials is beyond life’s control, the average temperature of our planet – and hence the coldness of the ice ages – is primarily determined by the amount of CO2 in the atmosphere. As this is potentially under biological control it looks like another example of a less than perfect outcome of the interactions between life on Earth and its environment.
Look further and you find still more examples. The scarcity of light at ground level in rainforests inhibits growth of all but the most shade-tolerant plants. There’s only really enough light for most plants at canopy height, often 20 to 40 metres up, or below temporary gaps in the canopy. The intensity of direct sunlight does not increase the higher you go, so having the bulk of photosynthesis taking place at such heights brings no great advantage to the forest as a whole. Rather the contrary, trees are forced to invest large amounts of resources in building tall enough trunks to have the chance of a place in the sun. This arrangement is hard to understand if you expect the environment to be arranged for biological convenience, but is easily understood as an outcome of plants competing for resources.
Source: “Not Quite Perfect”, Planet Earth Online: http://planetearth.nerc.ac.uk/features/story.aspx?id=1492&cookieConsent=A