Meeting this challenge would also help address the problem of world hunger because if we are to feed the developing world, we must abandon the intuitive, but naive, idea that producing cheap food will eliminate hunger. We've already made food cheap and there are still plenty of hungry people on the planet. A different approach-one that might actually work-is to promote the prosperity of small farms in developing countries. We need to enable peasant farmers to feed themselves, and generate an income capable of lifting them out of poverty while making them stewards of the land through access to knowledge, the right tools, and enough land to both feed themselves and grow a marketable surplus.

As much as climate change, the demand for food will be a major driver of global environmental change throughout the coming decades. Over the past century, the effects of long-term soil erosion were masked by bringing new land under cultivation and developing fertilizers, pesticides, and crop varieties that compensate for declining soil productivity. However, the greatest benefits of such technological advances accrue in applications to deep, organic-rich topsoil. Agrotech fixes become progressively more difficult to maintain as soil thins because crop yields decline exponentially with soil loss. Coupled with the inevitable end of fossil-fuel-derived fertilizers, the ongoing loss of cropland and soil poses the problem of feeding a growing population from a shrinking land base. Whereas the effects of soil erosion can be temporarily offset with fertilizers and in some cases irrigation, the long-term productivity of the land cannot be maintained in the face of reduced soil organic matter, depleted soil biota, and thinning soil that so far have characterized industrial agriculture.

Many factors may contribute to ending a civilization, but an adequate supply of fertile soil is necessary to sustain one. Using up the soil and moving on to new land will not be a viable option for future generations. Will modern soil conservation efforts prove too little and too late, like those of ancient societies? Or will we relearn how to preserve agricultural soils as we use them even more intensively? Extending the life span of our civilization will require reshaping agriculture to respect the soil not as an input to an industrial process, but as the living foundation for material wealth. As odd as it may sound, civilization's survival depends on treating soil as an investment, as a valuable inheritance rather than a commodity-as something other than dirt.

2. SKIN OF THE EARTH.

i. Darwin 1881, 4.

2. Darwin 1881, 313.

3. RIVERS OF LIFE.

I. Wallace 1883, 15.

2. Helms 1984, 133.

3. Lowdermilk 1926, 127, 129.

4. GRAVEYARD OF EMPIRES.

i. Xenophon Oeconomicus 16.3.

2. Plato Critics 3.111.

3. Varro De re rustica 1.3.

4. Varro De re rustica 1.2.6.

5. Columella De re rustica 1.7.6.

6. Tacitus Annals 3.54.

7. Tertullian De anima 30.

8. Simkhovitch 1816, 2og.

9. Tacitus Annals 2.59.

io. Marsh 1864, 9, 42.

11. Lowdermilk 1953, 16.

12. On fields, Exodus 23:Io-H; and on compost, Isaiah 25:10.

13. Lowdermilk 1953, 38.

14. Cook 1949, 42.

5. LET THEM EAT COLONIES.

I. Simkhovitch 1913, 400.

2. Markham 1631, 1, 3.

3. Evelyn 1679, 288-89, 295.

4. Evelyn 1679, 298, 315.

5. Mortimer 1708, 12.

6. Mortimer 1708, 14.

7. Mortimer 1708, 79.

8. Surell 1870, 135.

9. Surell 1870, 219.

10. Marsh 1864, 201.

ii. Brown 1876, Io.

12. Melvin 1887, 472.

13. Hutton 1795, 205.

14. Playfair 1802, 99.

15. Playfair 1802, Io6-7.

16. G.o.dwin 1793, 2:861.

17. Marx 1867, 638.

6. WESTWARD HOE.

I. Craven 1925, 19.

2. Beer 19o8, 243.

3. Craven 1925, 41.

4. Hartwell, Blair, and Chilton 1727, 6, 7.

5. Phillips 1909, 1:282.

6. Eliot 1934, 223-24- 7. Hewatt 1779, 2:305, 306.

8. Brissot de Warville 1794, 1:378.

9. Craven 1833, 150.

Io. Toulmin 1948, 71.

ii. Washington 1803, 6.

12. Washington 1892, 13:328-29.

13. Jefferson 1894, 3:190.

14. Washington 1803, 103-4*

15. Jefferson 1813, 509.

16. Taylor 1814, 11, 15, 10.

17. de Beaujour 1814, 85-86.

18. Lorain 1825, 240.

19. Phillips 1909, 1:284-85.

20. Craven 1925, 81.

21. Letter from Alabama 1833*

22. Ruffin 1832, 15.

23. C. Lyell 1849, 2:24.

24. C. Lyell 1849, 2:36.

25. C. Lyell 1849, 2:72.

26. U.S. Senate 1850, 7-8.

27. U.S. Senate 1850, 9.

28. White 1910, 40, 45*

29. Glenn 1911, 11, 19.

30. Hall 1937, 1.

7. DUST BLOW.

i. Johnson 1902, 638, 653.

2. Shaler 1905, 122-24, 128.

3. Shaler 1891, 330.

4. Shaler 1891, 332.

5. Davis 1914, 207, 213.

6. Davis 1914, 216-17- 7. Throckmorton and Compton 1938, 19-20.

8. Great Plains Committee 1936, 4.

9. Sampson 1981, 17.

1o. Lowdermilk 1953, 26.

IL Schickele, Himmel, and Hurd 1935, 231.

12. National Research Council ig8g, 9.

13. Ponting 1993, 261-62.

8. DIRTY BUSINESS.

i. Liebig 1843, 63.

2. Hilgard ,86o, 361.

3. Jenny 1961, 9-10.

4. Whitney 1909, 66.

5. van Hise 1916, 321-22.

6. USDA 1901, 31.

7. Whitney 1925, 12, 39.

8. Crookes 1900, 6, 7.

9. Smil 2001, 139.

Io. Howard 1940, 4.

11. Howard 1940, 219-20.