Consider soils that have just been born so that no eluviation, leaching, or illuviation has taken place. These are the entisols, the youngest soil order. The word entisol is derived from the word recent. In other words, entisols are recently born soils. Now suppose some eluviation, leaching, and illuviation has taken place so that the soil has horizons, although they are still immature horizons. These are young soils, and six soil orders are in this category: andisols, aridisols, gelisols, histosols, inceptisols, and vertisols. The andisols are the volcanic ashes. The word andisol is derived from the Andes Mountains where there is active vulcanism. The aridisols are soils found in deserts. The word aridisol is derived from the word arid meaning dry. The gelisols are the soils above permafrost. The word gelisol is derived from the Latin root gel- meaning cold. For example, a gelatin dessert is a cold dessert. The rejuvenation of dead gelisols is not primarily due to bioturbation but due primarily to cryoturbation instead, also known as frost churning. During the nighttime season, the gelisols freeze. During the next daytime season, the gelisols thaw. During the next nighttime season, the gelisols freeze again, and during the next daytime season, the gelisols thaw again. This is cryoturbation or frost churning, the mixing and hence rejuvenating of dead gelisols by the seasonal freezing and thawing of the soil. The histosols are organically rich soils found in wetlands (swamps, marshes, and quagmires). The word histosol is derived from the Greek root histo- meaning living tissue. For example, histology is the study of living tissue, and a histologist is someone who studies living tissue. The word inceptisol is derived from the word inception, although note that inceptisols are not quite newly born soils. These soils are called inceptisols not because the soil is newly born but because the horizons within the soil are newly born. Now suppose these young soils are subjected to further eluviation, leaching, and illuviation. The soil thus develops mature horizons, and hence these soils are the most agriculturally productive soils. There are two soil orders in this category: the alfisols and the mollisols. The word alfisol is derived from a combination of the words aluminum and ferrum, the Latin word for iron, since these alfisols have optimum amounts of inorganic minerals in addition to optimum amounts of air, water, and organic materials. The word mollisol is derived from the Latin root moll- meaning soft. For example, to mollify someone is to appease (to soften) their strong emotions, an emollient is a moisturizer that softens skin, and mollusks are invertebrate animals with soft bodies such as squid, octopi, snails, and slugs. The optimum amounts of inorganic minerals, air, water, and organic materials give mollisols a soft texture. These alfisols and mollisols are found abundantly in the midwestern United States, which is one of several reasons why American farmers are able to produce enough food in just a handful of midwestern states to feed the entire world. These soils are so rich that they have a deep black color. We are all strongly urged to take a road trip across the midwestern United States so that we can see these alfisols and mollisols with our own eyes. We will also see with our own eyes that the most abundant crop produced in the United States (and the entire world) is corn, with no other crop being produced anywhere nearly as abundantly. Now suppose these soils are subjected to even more eluviation, leaching, and illuviation. The result is old, dying soils. There are two soil orders in this category: the spodosols and the ultisols. The word ultisol is derived from the word ultimate, although note that ultisols are not quite dead soils. When soil is subjected to a maximum amount of eluviation, leaching, and illuviation, the soil is dead. These are the oxisols, the oldest soil order. These oxisols are found in tropical forests at the equatorial low where there is the most amount of rain in the entire world. The word oxisol is derived from the word oxidation, since the oxygen within the overabundant water has reacted (oxidized) with the soil to result in large amounts of metal oxides within the soil. Since woodlands are just outside of forests, spodosols and ultisols are found in woodlands where the precipitation is high but not as high as in forests. To summarize, the youngest soil order is the entisols, the slightly older but still immature soil orders are andisols, aridisols, gelisols, histosols, inceptisols, and vertisols, the mature soil orders that are best for agriculture are the alfisols and the mollisols, the dying yet still alive soil orders are spodosols and ultisols, and the oldest soil order is the oxisols. The most agriculturally productive soils are the alfisols and the mollisols, while the least agriculturally productive soils are the entisols (since these are newly born soils) and the oxisols (since these are dead soils).