Biosphere

Thanks to the life-giving qualities of air and water, Earth is populated by countless species of plants and animals. This horde of organisms comprises the biosphere. Most of the planet’s life is found from three meters below the ground to thirty meters above it and in the top two hundred meters of the oceans and seas.

In regard to the life-forms that make up the biosphere, have you ever asked what life is? What does it mean to be alive? Have you ever tried to define life? If so, how did you define it? If these questions strike you as odd, consider them for a moment (they are almost as difficult as defining the origin of life). Of course, we all have an intuitive sense of what life is, but if you had difficulty, as is probably the case, with answering these questions, you are not alone. These questions are open to debate and have been from the beginning of time. One thing is certain; life is not a simple concept, and it is impossible to define.

Along with the impossibility of defining life precisely, it is not always an easy thing to tell the difference among living, dead, and nonliving things. Prior to the seventeenth century, many people believed that nonliving things could spontaneously turn into living things. For example, it was believed that piles of straw could turn into mice. Obviously, that is not the case. There are some very general rules to follow when trying to decide if something is living, dead, or nonliving. Scientists have identified seven basic characteristics of life. Keep in mind that, for something to be described as living, that something must display all seven of these characteristics (i.e., ‘‘characteristic’’ is plural). Although many of us have many different opinions about what ‘‘living’’ means, the following characteristics were designated ‘‘characteristics of living things’’ with the consensus of the scientific community.

• Living things are composed of cells: living things exhibit a high level of organization, with multicellular organisms being subdivided into cells, and cells into organelles, and organelles into molecules, and so forth.

• Living things reproduce: all living organisms reproduce, either by sexual or asexual means.

• Living things respond to stimuli: all living things respond to stimuli in their environment.

• Living things maintain homeostasis: all living things maintain a state of internal balance in terms of temperature, pH, water concentrations, and so on.

• Living things require energy: Some view life as a struggle to acquire energy (from sunlight, inorganic chemicals, or another organism) and release it in the process of forming adenosine triphosphate (ATP). The conventional view is that living organisms require energy, usually in the form ATP. They use this energy to carry out energy-requiring activities such as metabolism and locomotion.

• Living things display heredity: living organisms inherit traits from the parent organisms that created them.

• Living things evolve and adapt: All organisms have the ability to adapt or adjust to their surroundings. An example of this is adapting to environmental change resulting in an increased ability to reproduce.

Interesting Point: Again, if something follows one or just a few of the characteristics listed above, it does not necessarily mean that it is living. To be considered alive, an object must exhibit all of the characteristics of living things. A good example of a nonliving object that displays at least one characteristic for living is sugar crystals growing on the bottom of a syrup dispenser. On the other hand, there is a stark exception to the characteristics above. For example, mules cannot reproduce because they are sterile. Another nonliving object that exhibits many of the characteristics of life is a flame. Think about it, a flame:

• respires,

• requires nutrition,

• reproduces,

• excretes,

• grows,

• moves,

• is irritable, and

• is organized.

We all know that a flame is not alive, but how do we prove that to the skeptic? The best argument we can make is as follows:

1. nonliving materials never replicate using DNA and RNA (hereditable materials); and

2. nonliving material cannot carry out anabolic metabolism.

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.

Hydrosphere

The hydrosphere includes all the waters of the oceans, lakes, and rivers, as well as groundwater—which exists within the lithosphere. Approximately forty million cubic miles of water cover or reside within the Earth. The oceans contain about 97 percent of all water on Earth. The other 3 percent is freshwater: (1) snow and ice on the surface of Earth contains about 2.25 percent of the water; (2) usable groundwater is approximately 0.3 percent; and (3) surface freshwater is less than 0.5 percent.

In the United States, for example, average rainfall is approximately 2.6 feet (a volume of 5,900 cubic kilometers). Of this amount, approximately 71 percent evaporates (about 4,200 cubic centimeters), and 29 percent goes to streamflow (about 1,700 cubic kilometers).

Beneficial freshwater uses include manufacturing, food production, domestic and public needs, recreation, hydroelectric power production, and flood control. Streamflow withdrawn annually is about 7.5 percent (440 cubic kilometers). Irrigation and industry use almost half of this amount (3.4 percent or 200 cubic kilometers per year). Municipalities use only about 0.6 percent (35 cubic kilometers per year) of this amount.

Historically, in the United States, water usage is increasing (as might be expected). For example, in 1975, 40 billion gallons of freshwater were used. In 1990, the total increased to 455 billion gallons. Projected use in 2002 is about 725 billion gallons. The primary sources of freshwater include the following:

1. captured and stored rainfall in cisterns and water jars;

2. groundwater from springs, artesian wells, and drilled or dug wells;

3. surface water from lakes, rivers, and streams;

4. desalinized seawater or brackish groundwater; and

5. reclaimed wastewater.

Atmosphere

The atmosphere is the body of air that surrounds our planet. But what is air? Air is a mixture of gases that constitutes the Earth’s atmosphere. What is the Earth’s atmosphere? The atmosphere is that thin shell, veil, or envelope of gases that surrounds Earth like the skin of an apple—thin, very thin—but very, very vital. The approximate composition of dry air is, by volume at sea level, nitrogen, 78 percent; oxygen, 21 percent (necessary for life as we know it); argon, 0.93 percent; and carbon dioxide, 0.03 percent, together with very small amounts of numerous other constituents (see table ). The water vapor content is highly variable and depends on atmospheric conditions. Air is said to be pure when none of the minor constituents is present in sufficient concentration to be injurious to the health of human beings or animals, to damage vegetation, or to cause loss of amenity (e.g., through the presence of dirt, dust, or odors or by diminution of sunshine).

Where does air come from? Genesis 1:2 states that God separated the water environment into the atmosphere and surface waters on the second day of creation. Many scientists state that 4.6 billion years ago a cloud of dust and gases forged the Earth and also created a dense molten core enveloped in cosmic gases. This was the protoatmosphere or proto-air, composed mainly of carbon dioxide, hydrogen, ammonia, and carbon monoxide, but did not last long before it was stripped away by a tremendous outburst of charged particles from the Sun. As the outer crust of Earth began to solidify, a new atmosphere began to form from the gases outpouring from gigantic hot springs and volcanoes. This created an atmosphere of air composed of carbon dioxide, nitrogen oxides, hydrogen, sulfur dioxide, and water vapor. As the Earth cooled, water vapor condensed into highly acidic rainfall, which collected to form oceans and lakes.

For much of Earth’s early existence (the first half ), only trace amounts of free oxygen were present. But then green plants evolved in the oceans, and they began to add oxygen to the atmosphere as a waste gas, and later oxygen increased to about 1 percent of the atmosphere and with time to its present 21 percent. How do we know for sure about the evolution of air on Earth? Are we guessing, using ‘‘voodoo’’ science? There is no guessing or voodoo involved with the historical geological record. Consider, for example, geological formations that are dated to two billion years ago. In these early sediments, there is a clear and extensive band of red sediment (‘‘red bed’’ sediments)—sands colored with oxidized (ferric) iron. Previously, ferrous formations had been laid down showing no oxidation. But there is more evidence. We can look at the time frame of 4.5 billion years ago, when carbon dioxide in the atmosphere was beginning to be lost in sediments. The vast amount of carbon deposited in limestone, oil, and coal indicate that carbon dioxide concentrations must once have been many times greater than today, which stands at only 0.03 percent. 

The first carbonated deposits appeared about 1.7 billion years ago, the first sulfate deposits about 1 billion years ago. The decreasing carbon dioxide was balanced by an increase in the nitrogen content of the air. The forms of respiration practiced advanced from fermentation 4 billion years ago to anaerobic photosynthesis 3 billion years ago to aerobic photosynthesis 1.5 billion years ago. The aerobic respiration that is so familiar today only began to appear about five hundred million years ago. The atmosphere itself continues to evolve, but human activities—with their highly polluting effects—have now overtaken nature in determining the changes. And, when you get right down to it, that is one of the overriding themes of this text—human beings and their affect on planet Earth. The atmosphere is an important geologic agent and is responsible for the processes of weathering that are continually at work on the Earth’s surface.

Gas Chemical     Symbol       Volume (%)

nitrogen                N2               78.08

oxygen                 O2                20.94

carbon dioxide     CO2               0.03

argon                   Ar                  0.093

neon                    Ne                  0.0018

helium                 He                 0.0005

krypton                Kr                 trace

xenon                  Xe                  trace

ozone                   O3               0.00006

hydrogen             H2               0.00005

Landforms

Based on personal experience, when introducing students to the geological and geographical aspects of environmental science initially, there is some confusion as to the exact difference between geology and geography. This is partially the case because, while there are several differences between the two sciences, they are also wed in many respects. To save on time and to avoid confusion, the best way to differentiate between the two sciences is to simply point out that for the purpose of this book geology is defined as the science that deals with the natural structure of Earth and geography deals with the human-drawn or human-made national borders and lines on Earth.

One thing is certain: certain aspects of geology, such as Earth’s internal forces involved in the building and development of mountains, continental plains, and coastal basins, are relevant to physical geography. Moreover, rock type and structure are important as variables that influence the effectiveness of rain, wind, and weathering processes on landforms.

We have all seen the photographs of the Earth taken from outer space; they show the surface of the Earth as being far from uniform. Earth’s surface is covered with natural features called landforms. These features are classified by type in order to describe them—mountains, valleys, plains, and so forth. The features’ names help us to locate specific places. Along with classification by type, landforms can also be classified and organized by the genetic processes that create them.

Genetic Landforming Processes

Genetic landforming processes work across the globe’s seven large landmasses, the continents. These processes include Aeolian landforms, coastal and oceanic landforms, erosion landforms, fluvial landforms, mountain and glacial landforms, slope landforms, and volcanic landforms. Genetic landforming processes and individual landforms are described in the following text; many of the individual landforms are described in greater detail later in the text. Keep in mind that many of the landforms listed and described below are produced by more than one landforming process. For example, landforms produced by erosion and weathering usually occur in both coastal and fluvial environments. However, to eliminate redundancy, each landform is only listed and described once under a specific process.

Volcanic Landforms

A volcanic landform is characterized by the type of material it is made of. Later processes modify the original landform to other forms. Volcanic landforms include the following:

• caldera—very large, cauldronlike depression that is usually formed by the collapse of land following a volcanic eruption. Calderas are enclosed depressions that collect rainwater and snowmelt, and thus lakes often form within a caldera.

• geyser—a hot spring characterized by intermittent discharge of water ejected turbulently and accompanied by steam.

• lava—molten rock.

• lava spine—an upright cylindrical mass of lava caused by the upward squeezing of pasty lava inside a volcanic vent.

• lava tube—a natural conduit through which lava travels beneath the surface of a lava flow, expelled by a volcano during an eruption.

• maar—a broad, low-relief volcanic crater that is caused by an explosion caused by groundwater coming into contact with hot magma.

• malpais—a landform characterized by eroded rocks of volcanic origin in an arid environment.

• mamelon—a hill formed by eruption of stiff lava.

• mid-ocean ridge—an underwater mountain range, typically having a valley known as a rift running along its spine, formed by plate tectonics.

• oceanic trench—narrow topographic depressions of the sea floor.

• pit crater—a depression formed by a sinking of the ground surface lying above a void or empty chamber.

• pseudocrater—a volcanic landform that resembles a true volcanic crater but differs in that it is not an actual vent from which lava has erupted.

• subglacial mound—a type of subglacial volcano that forms when lava erupts beneath a thick glacier or ice sheet.

• tuya—a distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet.

• volcanic dam—a natural dam produced by volcanic activity.

• volcanic field—a spot of the Earth’s crust that is prone to localized volcanic activity.

• volcanic plateau—a plateau produced by volcanic activity.

• volcanic plug—a volcanic landform created when magma hardens within a vent on an active volcano.

Slope Landforms

Generally, when discussing slope, we are primarily concerned with hillslopes—that is, the slopes connecting hilltops with river channels in valley bottoms. Slopes include slopes created by river sediments, rainwash, and rockfall (talus). Although discussed in detail later in the text, it should be pointed out that slope has a great influence on mass movement and wasting. Slope not only influences the evolution of landforms but also gives geologists important information about the formation of landforms. Slope landforms include the following:

• alas—a steep-sided depression formed by the melting of permafrost; it may contain a lake.

• defile—a narrow pass or gorge between mountains or hills.

• dell—a small wooded valley.

• escarpment—a transition zone between different provinces that involves a sharp, steep elevation differential, characterized by a cliff or steep slope.

• glen—a valley, typically one that is long, deep, and often glacially U-shaped.

• gully—a landform created by running water eroding sharply into soil, typically on a hillside.

• hill—a landform that extends above the surrounding terrain, in a limited area.

• knoll—a small, natural hill.

• mountain pass—a saddle point in between two areas of higher elevation.

• ravine—a very small valley, which is often the product of stream-cutting erosion.

• ridge—a geological feature that consists of a continuous, elevational crest for some distance.

• rock shelter—a shallow cavelike opening at the base of a bluff or cliff.

• scree—an accumulation of broken rock fragments at the base of mountain cliffs.

• vale—a wide river valley, with a particularly wide floodplain or flat valley bottom.