No, don’t be ridiculous
Everybody remembers the lines by Wordsworth: “I wandered lonely as a cloud/That floats on high o’er vales and hills”. Granted his poem is about the eternal significance of daffodils, but a world without clouds would be like Los Angeles, very dull indeed. No towering cumulo-nimbus above English watermeadows, nor the majesty of vast anvil-thunderheads at sunset. So too, no membranous cirrus stretching far beyond reach, not even the calm of a mackerel sky as the evening crows fly home past the church tower that was old at the time of Agincourt. In the hands of painters like John Constable and Samuel Palmer clouds come alive, but they themselves are mere water vapour and ice-crystals, as dead as a diamond.
Yes, of course
Consider now these lines: “I am the daughter of Earth and Water,/And the nursling of the Sky;/I pass through the pores of the ocean and shores;/I change, but I cannot die.” Well, unlike Wordsworth, Shelley is writing specifically about clouds but he is not providing us with high-rhetoric meterology, but once again touching on much deeper matters. Maybe there is also more to a cloud itself than first meets the eye? Yes, clouds are water vapour and ice-crystals, but so too they carry a freight of bacteria and other microbes. But are these microorganisms accidental passengers or can they make the clouds their home? There is a simple test. If the microbes are metabolically active then this will register in the changing chemistry of the clouds. Thus, carbon compounds will be degraded and free radicals (such as hydrogen peroxide) – that otherwise would be dangerous to any microbe – should be mopped up. So too nitrogen will be transformed into nitrates. Given they are a key agricultural fertilizer then perhaps clouds are more fertile than we thought?
When Shelley began The Cloud with the line “I bring fresh showers for the thirsting flowers”, he not only made the point that goodness could rain from the heavens but what goes up must come down. Now here’s a simple question. What is the freezing point of water? Well done, zero Celsius is the answer. Why then is that drop of water at minus twenty Celsius and still stubbornly remaining in liquid form? In the trade it is known as supercooled water. The reason is that unless the temperatures are really perishing (say -30oC), ice will only readily form if it can nucleate on to something. Let’s imagine you are a gardener and a sharp frost has just ruined your potatoes. Who’s to blame? Look carefully at the surface of the leaves; they are crowded with bacteria. Some have the neat trick of synthesizing a protein that includes an array of amino-acids which are so arranged as to form a template on which ice can nucleate. Why do the bacteria do this: do they plan to go skating? No, the growth of the ice-crystals serves to break through the tough cell walls of the plant giving access to delicious interior. Now suppose that such bacteria are swept high into the air. This readily happens, and once in the clouds the knack these bacteria show of nucleating ice-crystals will find immediate service.
It all depends on the question
But it gets better. So far the emphasis has been on microbes, but fungi can join in the fun. As flying mushrooms? Not quite; it is myriads of minute spores that are wafted high in the air. Just as their release from the fruiting body depends on a clever use of tiny water droplets (and a resultant acceleration that would do credit to a rocket), so high in the atmosphere water vapour readily recondenses on the spore and one is well on one’s way to making a raindrop. So there is a perpetual cycle of tiny organisms carried aloft to clouds that then return in the rain, but they also need to find new homes, new resources. This, however, leads to some potentially tricky territory. It revolves around the following question: Is life on this planet just a passenger, albeit seeking homes as diverse as hot-springs, oceans, and those clouds? Or does it engineer the system for its own benefit, as James Lovelock’s Gaia hypothesis would argue? In this context consider the molecule DMS, short for dimethyl sulphide ((CH3)2S).
Its distinctive odour explains why cooking cabbage can smell so horrible, but DMS is also released by marine plankton. It sounds far fetched that the DMS could assist in the airborne dispersal of marine microorganisms by increasing wind speeds. Or is it? The idea is less daft when we realize that when the DMS is oxidized a net result is the formation of minute droplets or aerosols. When they condense latent heat is released into the atmosphere, thus providing enough energy to generate a stiff breeze. In this manner the microbes can be wafted to far destinations. Biological activity does not proceed to the background of an uncaring world but actually is intimately related to things like clouds and winds. Seeing clouds as alive offers us new perspectives on both the interconnectedness of the biosphere and the complex epicycles of existence. These exchanges may not only be vital to the economy of the planet, but explain the origin of vitality itself.
In the beginning there was an Earth and its oceans, but despite an abundance of organic molecules, no life. Consider how aerosols might be lofted from the ocean, not as just minute water droplets but coated by surfactants (the key ingredient of detergents, such as palmitic or stearic acid) that make the surface water-repellent (hydrophobic). These aerosols would enclose a tiny aqueous laboratory, a location for organic synthesis. Climbing in their uncounted trillions into the sky, ultra-violet radiation from the Sun would power chemical pathways generating more complex compounds, while opportune freezing could preserve fragile molecules until the rain returns these micro-laboratories to the ocean. And so it would go on. No longer do we have to wait nervously at the edge of that warm, little Darwinian Pond, hoping that a few throws of the dice will come up trumps and provide us with the first cell. In this very different scenario immense numbers of aerosols cycle ceaseless across vast eons of time. So large is the number of “experiments” (one calculation suggests about 1032 attempts) that the question of the origin of life moves from one of fantastic improbability to almost inevitable. If so will not the same process occur on any Earth-like planet? Strewn across the Galaxy will there not be biospheres beyond count?
Text copyright © 2015 Simon Conway Morris. All rights reserved.
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