Astronaut Neil Armstrong tells how, once during a mission, he raised his thumb in front of one eye to blot out his view of the Earth. In December 1972, the crew of the Apollo 17 spacecraft took the, now famous, ‘blue marble’ photograph of Earth from a distance of about 45,000 kilometres as they travelled towards the moon on what is still the most recent manned moon mission. Leaving our planet was not just an incredible technological achievement but a turning point - our home revealed for what it really is - an insignificant speck in the vastness of space. Insignificant in some ways perhaps, but a place where life, in all its complexity, has evolved. As yet we don’t know if Earth is a one-off, never to be repeated fluke of unimaginable rarity - a planetary nonpareil - or just one of billions upon billions of rocky planets where living organisms abound. We may never know.
So, what sustains life on Earth? The answer is mud - a mixture of soil and water. These are the fundamental natural resources which nourish and support terrestrial ecosystems and give us the food we need to survive. The trouble is, both these commodities, essential to our continuing existence are in finite supply.
One biologist, tired of the top-billing and research grants given to some of the Earth’s more glamorous habitats, described soil as the poor man’s rain forest on account of the fact that we know so little about what goes on in its dark nooks and crannies. He argued that it contained just as much biodiversity and was probably more important than a rain forest in the greater scheme of things. Beginning with the gradual wearing down of mountains by wind and rain, soil is formed by complex physical and chemical processes and the painfully slow accumulation of organic matter. If the Earth’s crust can be likened to a sheet of paper stuck to the outside of a football, then the soil that covers parts of it is nothing but an insubstantial smear of almost indescribable fragility. For a natural resource that we could never manufacture and that does so much for us we pay it scant attention. Providing anchorage and nutrients for all plant life, ameliorating the effects of pollutants, purifying ground waters and recycling dead organisms - life on land depends on it.
We may however have reached a tipping point where soil is being lost faster than it is being formed. A few years ago, I remember watching a news broadcast where the Mayor of a small French town was lamenting the giant mudslide that had engulfed his home, killing hundreds and leaving many more homeless. The camera panned slowly up to the hills above the village from where the death-dealing deluge had come. “We cannot understand why this has happened.” the Mayor said. But the answer was all too clear. Trees that once clothed the slopes above the town, anchoring the soil and releasing heavy rainfall in gentle streams had been cleared. It has been an often-repeated recipe for disaster ever since cultivation and forest clearance first began. Anywhere that soil is exposed, especially on slopes, it is liable to be washed away either to where it is not wanted or more often, to where it is inaccessible. You can easily measure the rate at which this happens. Take a litre of water from a stream or river and boil it dry. Weigh the solid material that you have left and estimate the flow rate of the river to get an idea of how much soil is going on a one-way trip to the ocean floor.
Today soil erosion leading to desertification is taking place all on every continent. Industrial-scale agriculture, effectively converting natural resources into human bodies, is mostly to blame. Every year more than 80 million more human beings need to be fed but at the same time 25 billion of tonnes of soil are being lost.
The other finite ingredient to our muddy life-support system is of course water. Our planet may look blue but around 97% of all Earth’s water is salty. Of the remaining 3%, which is freshwater, most is currently locked up in the polar ice caps, deep in underground aquifers, wetlands or permafrost, in the atmosphere or already contained in the tissues of living organisms. The actual amount of freshwater in rivers and lakes that you could dip a cup into to slake your thirst (assuming it was clean and safe to drink) is less than 100,000 cubic kilometres. That may sound a lot, but it’s less than half a percent of all the freshwater that exists and not much when you consider the growing demands on it. Seven times more drinking water is needed now than one hundred years ago. Increasing the availability of freshwater by towing icebergs around the planet or the use of giant desalination plants would be prohibitively expensive so we are stuck with what we’ve got. One of the problems with the supply of that freshwater is that it is very unevenly distributed. More than a quarter of the world’s freshwater can be found in the great rivers and lakes of South America and yet the human population there is actually relatively small. Elsewhere the story is very different with multitudes in Asia clamouring for an ever-decreasing supply. Even large rivers can run completely dry before they reach the sea, as more and more water is taken for irrigation. Another problem is that rivers pay no heed to political boundaries as they flow from source to sea and too much taken out upstream will result in a reduction in flow downstream. When this happens, you can be sure of trouble. Already there have been several hundred international disputes over water supplies and they look likely to increase in the future. The human population has more than doubled in my lifetime and it looks like we may be heading towards a population of nine billion…but only if we have enough mud.