Saturday, 15 August 2015

Living planet: lightning

Image result for lightning lifeDiscounting humans almost all forest fires are caused by lightning, which strikes the planet 100 times a second, or 3 billion times a year.  The lightning also converts atmospheric nitrogen into  a form which can be used by life. Without these strikes it is questionable whether plants and animals would have appeared, or anything that we would recognize as a thriving biosphere.

Apart from joining with thunder  to create awe and wonder in the consciousness of sentient beings witnessing a thunderstorm lightning has physical effects which are, and for millions of years have been, of critical importance to the biosphere.

First, the heat generated in the air (comprising 78% nitrogen)  breaks down the triple bond which holds together  the 2 nitrogen atoms in each molecule of nitrogen so tightly that they cannot be used by the living organisms which need them. Without this bond being broken down there would be no life.  There also has to be rain to dissolve the nitrogen atoms and take them down to the soil where they can be acted upon by bacteria and taken into the cycle of processes by which plants are made. Animals and humans eat the plants, so they depend on the same nitrogen atoms released from the triple bonds. 

(The whole process by which nitrogen is taken from the atmosphere, used by the living world, and returned to the atmosphere is known as the nitrogen cycle. This feedback mechanism has kept the optimum concentration of nitrogen in the air at 78 % over millions of years.)

There is another way in which the triple bonds holding N (nitrogen) atoms together can be broken. This requires the action of bacteria on the tightly bonded molecules to produce ammonia . Ammonia contains 1 N atom and 4 H (hydrogen) atoms but the N is easy to extract from the ammonia for use by living systems.  This  process does not appear to involve lightning but is this really the case? It requires bacteria to produce the ammonia; yet bacteria are living organisms and all organisms require N freed from its triple bond.

I am not a qualified biologist so please pull me up if I am wrong but it does seem to me that without lightning there would have been no bacteria to extract N from the atmosphere for use by other bacteria in the first step of the protein  building process on which plants and, ultimately, animals depend. If this is right then all living systems, from microbes to mammals, depend on lightning strikes, either taking place now or having done so in the remote past.

Image result for lightning life
Some scientists speculate that electrical discharges in the primeval atmosphere, consisting of water vapour, ammonia and carbon dioxide, somehow sparked off a process which led to living organisms. The odds against this are breathtakingly astronomical unless one invokes the quantum realm and this means bringing in agents outside the natural order of objective, directly empirically testable science.

Returning to the present biosphere lightning is the main cause of wildfires, apart from human beings in the geologically very recent past . This is another way in which electrical discharges are an indirect but important agent in  the living world.  Forest fires remove various growth inhibitors and infuse the soil with water-retaining, mineral –rich charcoal. The fires also facilitate the growth of fungi which help produce more nitrogen in the form which is right for life.

Finally, lightning and rain cooperate  to reduce air pollution. The sparks fuse dust and pollen particles together, making them heavier and able to be washed out of the atmosphere. This is why the air is fresher  following  a thunderstorm than after ordinary rain.

John Sears