The Earth’s supply of natural resources is limited. This is obvious and yet everyone not from a farm thinks you can just start farming wherever there is some dirt. However, farmers go to where there is good dirt, and they do so rather quickly and fill up the land. This is shown graphically with the chart below of the history of the California farm land. When gold was discovered in California in 1849 there was a terrific migration from all over the world; they came for the opportunity to get rich. What turned out to be the really big money maker was the land itself, and a country which was almost exclusively Spanish cattle ranches exporting cattle hides up until that date suddenly with the coming of the Americans came under agriculture. In 30 years the land under cultivation grew from near zero in 1849 to 3,800,000 acres by 1879. It continued to grow at that spectacular rate for another twenty years and by 1899 there were 7,100,000 acres being cultivated but then in another eighty years it grew to 9,000,000 acres and then fell back to what looks like 8,500,000. A quick look at the chart below shows essentially no new farmland for 50 years and very little for 100 years. Furthermore as cities and highways grow, as they currently are, they tend to consume the very best of the farmland and cities are growing rapidly.
Source: Creating abundance: biological innovation and American agricultural development by Alan L. Olmstead, Paul W. Rhode. p. 225
California was one of the last places on Earth to come under intensive cultivation. When this land filled up the population of the Earth was about 1.650 billion; it is now about 6.8 billion, and just in case you weren’t counting that is 4.1 times as many people and essentially no new dirt upon which to grow the food to feed those extra people. Our farmers and their technology are now able to wring that extra food out of the same amount of soil as their great grandfathers were tilling. However, this increase can’t go on forever because of several problems, such as when soil is irrigated the salt in the fresh water stays in the soil. That isn’t a problem for several years but there comes a time when it becomes so severe that the crops that were grown successfully for a hundred years will no longer produce. A second problem is that the nutrients in the soil get used up by the crops and need to be replenished with fertilizers which requires lots of petroleum, and the farms must be cultivated with machinery which also requires petroleum for fuel. There is still plenty of petroleum available for farming, but not an infinite amount, and it may only be economical to farm this way for another hundred years, probably much less.
At the moment everything is wonderful, and getting better, but it cannot last forever, and when the world supply of cheap oil power comes to an end, and food becomes more expensive, there will come a time when food itself comes into short supply and there will have to be a change in the way things are done. Now is the time to prepare for that eventuality while there is still plenty of surplus time, energy and money. Oh, yes there is plenty of money for the tiny Earth Ark projects, but there isn’t plenty of time.