Salt in Soil and the Mystery of Life

[chris]

A few weeks ago I was thinking about iboga extraction. I had developed the extraction using vinegar and ammonia because it seemed to work fine, and the waste stream was safe and effective for use as fertilizer since it would fully biodegrade. When I recently tried the extraction with hydrochloric acid, that worked better, but I was concerned with how the chloride from the hydrochloric acid would be dealt with by the environment, since putting salt in soil is well known to prevent plants from growing in it. But it also seems obvious that the ability of salt to prevent plant growth should depend on the amount of rainfall the soil is exposed to, since nothing prevents the salt, once dissolved, from being completely leached from the soil into the ground water. Washing salt into the ground water would not be a problem except for the eventual salinification of the ground water, which itself would not be a problem if the ground water were not pumped back to the surface at wells for human use.

What puzzles me though is how essential ions, like sodium and potassium for example, which are almost impossible to render insoluble, prevent being completely leached from soil and made unavailable to life on it. Back when salt was more precious than gold, why was it only humans that were having a hard time surviving on the salt in their diet, having to trek to the nearest ocean to supplement it? What did humans do before they knew to find salt in the ocean? The mineral composition of blood has been compared to that of sea water, as if to imply that life evolved in the oceans until finding a way to carry a bit of the ocean inside each creature. I suppose eating enough meat would pass on the salt therein, but where does it enter the system? Each urination, each creature that dies uneaten, allows salt to leach into ground water irreversibly forever. How do plants and insects, the beginning of the food chain, obtain salt far inland? The rain cycle is like an enormous Soxhlet extractor, removing soluble ions from the surface of the Earth and accumulating them in lakes, ground water and the ocean. Given enough time - and it shouldn't take much - all water soluble ions should be separated, leaving any life dependent on them impossible, unless it happens to have access to lakes, ground water or the ocean. Yet life persists. The only explanation I can think of is that some salt may enter the air as particulates - salt spray. I've never heard of this, and it seems unlikely, but I don't know how else to explain that life is still here.

[chris]

Talking with my wife, the Environmental Scientist, about this brought the suggestion that the essential elements like sodium, potassium, chloride and iodide are released from rock as it degrades and this is what keeps terrestrial life alive. The frightening implication is that it also makes terrestrial life unsustainable, since the amount of these elements in top soil rock is quite finite, and the "time left" could be easily calculated from average rock composition and the RDA for soluble minerals. Actually, this would be the upper limit of time left, since the amount of elements released would likely usually be more than need3ed for survival, most of which would be incorporated into inedible plant parts and lost (as in the case of the potassium in potash), and since mammals require many of these elements to survive, they would perish once any of them drops below the level needed for survival. Amazing we've made it this far!

[Matt S]

You know when I first read this a while back I was reminded of places like hotsprings where salty water arises from deep within the earth. The Earth remakes itself over time with volcanic activity and tectonic plate activity. Why would there be a limited amount of time left?

[chris]

There are places, like the shore, where essential minerals are always available, forever dissolved in the ocean. But most of the land, except as irrigated by man, is not exposed to any water except for rain water, which contains no minerals. Rocks tend to contain elements like silicon, calcium, aluminum, etc., which can form salts which dissolve very poorly in water. This allows the rocks to not dissolve when it rains. There may be a tiny amount of sodium, potassium, etc., in rocks, but it can only leach out once and then be washed into the ground water, never to return to the topsoil. I've always wondered what makes desert "infertile" and I suspect it is this. I'm not sure how long it takes for continents to be churned back into the ocean or mountains and volcanoes to form these days, or how much of the crust is still affected. This is just a curiosity, really. Mainly I'm just surprised that life is as widespread as it is, rather than having mostly desert on the land except for some rings around the coasts, lakes and rivers. I just like to understand.