Lithosphere

The lithosphere is of prime importance to the geologist and geographer. This, the solid, inorganic, rocky crust portion of the Earth, is composed of rocks and minerals that, in turn, comprise the continental masses and ocean basins. The rocks of the lithosphere are of three basic types: igneous, sedimentary, and metamorphic.

Soil Geology

We use soil for our daily needs, but we do not sufficiently take account of its slow formation and fast loss. Simply, we take soil for granted. It’s always been there—with the implied corollary that it will always be there—right? But where does soil come from?

Of course, soil was formed, and in a never-ending process, it is still being formed. However, as mentioned, soil formation is a slow process—one at work over the course of millennia, as mountains are worn away to dust through bare rock succession. Any activity, human or natural, that exposes rock to air begins the process. Through the agents of physical and chemical weathering, through extremes of heat and cold, through storms and earthquake and entropy, bare rock is gradually worn away. As its exterior structures are exposed and weakened, plant life appears to speed the process along.

Lichens cover the bare rock first, growing on the rock’s surface, etching it with mild acids and collecting a thin film of soil that is trapped against the rock and clings.This changes the conditions of growth so much that the lichens can no longer survive and are replaced by mosses.

The mosses establish themselves in the soil trapped and enriched by the lichensand collect even more soil. They hold moisture to the surface of the rock, setting up another change in environmental conditions. Well-established mosses hold enough soil to allow herbaceous plant seeds to invade the rock. Grasses and small flowering plants move in, sending out fine root systems that hold more soil and moisture, and work their way into minute fissures in the rock’s surface. More and more organisms join the increasingly complex community.

Weedy shrubs are the next invaders, with heavier root systems that find their way into every crevice. Each stage of succession affects the decay of the rock’s surface and adds its own organic material to the mix. Over the course of time, mountains are worn away, eaten away to soil, as time, plants, weather, and extremes of weather work on them.

The parent material, the rock, becomes smaller and weaker as the years, decades, centuries, and millennia go by, creating the rich, varied, and valuable mineral resource we call soil.

Perhaps no term causes more confusion in communication between various groups of average persons, soil geologists, soil scientists, soil engineers, and Earth scientists than the word soil. In simple terms, soil can be defined as the topmost layer of decomposed rock and organic matter that usually contains air, moisture, and nutrients and can therefore support life. Most people would have little difficulty in understanding and accepting this simple definition. Then why are various groups confused on the exact meaning of the word soil? Quite simply, confusion reigns because soil is not simple—it is quite complex. In addition, the term soil has different meanings to different groups (like pollution, the exact definition of soil is a personal judgment call). Let’s take a look at how some of these different groups view soil. 

Average people seldom give soil a first or second thought. Why should they? Soil isn’t that big a dea —that important—it doesn’t impact their lives, pay their bills, or feed their bulldog, right? Not exactly. Not directly.

The average person seldom thinks about soil as soil. He or she may think of soil in terms of dirt but hardly ever as soil. Why is this? Having said the obvious about the confusion between soil and dirt, let’s clear up this confusion.

First of all, soil is not dirt. Dirt is misplaced soil—soil where we don’t want it, contaminating our hands and fingernails, clothes, and automobiles and tracked in on the floor. Dirt is what we try to clean up and to keep out of our living environments. Secondly, soil is too special to be called dirt. Why? Because soil is mysterious and, whether we realize it or not, essential to our existence. Because we think of it as common, we relegate soil to an ignoble position. As our usual course of action, we degrade it, abuse it, throw it away, contaminate it, ignore it—we treat it like dirt, and only feces hold a more lowly status than it does. Soil deserves better.

Why?

Again, because soil is not dirt—how can it be? It is not filth, or grime, or squalor. Instead, soil is clay, air, water, sand, loam, organic detritus of former life-forms (including humans), and most important, the amended fabric of Earth itself; if water is Earth’s blood, and air is Earth’s breath, then soil is its flesh and bone and marrow—simply put, soil is the substance that most life depends on. Soil scientists (or pedologists) are people interested in soils as a medium for plant growth. Their focus is on the upper meter or so beneath the land surface (this is known as the weathering zone, which contains the organic-rich material that supports plant growth) directly above the unconsolidated parent material. Soil scientists have developed a classification system for soils based on the physical, chemical, and biological properties that can be observed and measured in the soil.

Soils engineers are typically soil specialists who look at soil as a medium that can be excavated using tools. Soils engineers are not concerned with the plant-growing potential of a particular soil but rather are concerned with a particular soil’s ability to support a load. They attempt to determine (through examination and testing) a soil’s particle size, particle-size distribution, and the plasticity of the soil.

Earth scientists (or geologists) have a view that typically falls between pedologists and soils engineers—they are interested in soils and the weathering processes as past indicators of climatic conditions, and in relation to the geologic formation of useful materials ranging from clay deposits to metallic ores.

Would you like to gain a new understanding of soil? Take yourself out to a plowed farm field somewhere, anywhere. Reach down and pick a handful of soil, and look at it—really look at it closely. What are you holding in your hand? Look at the two descriptions that follow, and you may gain a better understanding of what soil actually is and why it is critically important to us all.

1. A handful of soil is alive, a delicate living organism—as lively as an army of migrating caribou and as fascinating as a flock of egrets. Literally teeming with life of incomparable forms, soil deserves to be classified as an independent ecosystem or, more correctly stated, as many ecosystems.

2. When we pick up a handful of soil, exposing Earth’s stark bedrock surface, it should remind us (and maybe startle us) to the realization that without its thin, living soil layer, Earth is a planet as lifeless as our own Moon.