Hovering in the back of my mind for some time now has been a quietly monumental idea that I read in Isaac Asimov's 1962 book Fact And Fancy. In the book's first essay, "Life's Bottleneck", Asimov lays out an astounding but logical notion: that the ultimate limiting factor for the amount of life on Earth is phosphorus, and that our supply is rapidly diminishing, thus constantly lowering the ceiling on the amount of life that the world can sustain.

In a nutshell, phosphorus is one of the most critical elements in the biological building blocks and processes in all life, and the amount required for plant & animal life to exist vs. the concentration of usable phosphorus in water and soil is the limiting factor in life's development on earth.

The issue that we face is the availability of that usable phosphorus. Asimov explains that, in effect, the world's phosphorus is steadily falling down to the bottom of the sea, where it is no longer usable and is not being recovered at a rate to balance out its loss.

The reason for this is that the movement of phosphorus is largely one-way. Asimov explains the example of phosphorus in soil:

The rain comes down, dissolves tiny quantities of soil, and on this solution, plants grow until all the phosphorus they can grab has been incorporated into their substance. Animals eat the plants and, in the process of living, excrete phosphorus-containing wastes upon which plant life can feed, grow, and replace the amount of itself which animals have eaten...

And just as there is a drizzle out of the euphotic zone of the ocean, so there is a drizzle out of the land. Some of the dissolved materials in the soil inevitably escape the waiting rootlets and are carried by the seeping soil water to brooks and rivers and eventually to the sea.

That might not sound like a dramatic process, but Asimov continues:

...it is estimated that 3,500,000 tons of phosphorus are washed from the land into the sea by the rivers each year. Since phosphorus makes up roughly 1 per cent of living matter, that means that the potential maximum amount of land-based protoplasm decreases each year by 350,000,000 tons.

Phosphorus is steadily being transferred from land to sea (through transmission into rivers, which in turn carry it to the sea), and from the upper parts of the ocean to the ocean floor. Once it reaches the ocean floor, which is already saturated with more phosphorus than can be used by the life present at that depth, it is essentially out of the reach of land-based life.

A point made by Asimov, and again this past week on the Treehugger web site, is that humans are literally flushing away vast amounts of phosphorus every day, through our modern plumbing and sewage systems. In the quote above, Asimov points out the natural flow of phosphorus from the soil through plant life to animal life and back to the soil. But our modern sewage systems take the phosphorus present in our own waste matter and send it directly into the sea--in essence, pouring our world's capacity for life on land literally down the drain.

What must be done about this and what can be done about this is a topic for another time (and some suggestions are noted in the previous paragraph's link). But the gravity of this idea is worth pondering--what other fundamental aspects of life on Earth are we affecting, completely unawares, through simple scale and seemingly unconnected behaviors?

Labels: Environment