How Do Earth’s Four Spheres Interact?
ENERGY AND MATTER MOVE between the land, water, atmosphere, and biosphere — between the four spheres. There are various expressions of these interactions, many of which we can observe in our daily lives. In addition to natural interactions, human activities, such as the clearing of rain forests, can affect interactions between the spheres. Changes in one component of one sphere can cause impacts that affect components of other spheres.
What Are Some Examples of Energy and Matter Exchanges Between Two Spheres?
The four spheres interact in complex and sometimes unanticipated ways. As you read each example below, think of other interactions — observable in your typical outdoor activities — that occur between each pair of spheres.
The Sun's energy evaporates water from the ocean and other parts of the hydrosphere, moving the water molecules into the atmosphere. The water vapor can remain in the atmosphere or can condense into tiny drops that form most clouds. Under the right conditions, the water returns to the surface as precipitation.
Active volcanoes emit gases into the atmosphere, and major eruptions release huge quantities of steam, sulfur dioxide, carbon dioxide, and volcanic ash. In contrast, weathering of rocks removes gas and moisture from the atmosphere. Precipitation accumulates on the land, where it can form standing water, groundwater, or erosion-causing runoff.
Plants and animals utilize precipitation from the atmosphere, and some plants can extract moisture directly out of the air without precipitation. Large-scale circulation patterns in the atmosphere are a principal factor in determining an area's climate, and the climate directly controls the types of plants and animals that inhabit a region.
Channels within a stream generally bend back and forth as the water flows downhill. The water is faster and more energetic in some parts of the stream than in others, and so erodes into the streambed and riverbank. In less energetic sections, sediment will be deposited on the bed, like the gravel in this photograph. Earth's surface can be uplifted or dropped down, as during an earthquake, and the resulting changes can influence the balance of erosion and deposition.
Oceans contain a diversity of life, from whales to algae, and everything in between. Coral reefs represent an especially life-rich environment, formed when living organisms extract materials dissolved in or carried by seawater, to produce the hard parts of corals, shells, and sponges. At greater ocean depths, where waters are colder, shells and similar biologic materials dissolve, transferring material back to the seawater.
The clearest interaction between the lithosphere and biosphere is the relationship between plants and soils. The type of soil helps determine the type of plants that can grow, and in turn depends on the type of starting materials (rocks and sediment), the geographic setting of the site (e.g., slope versus flat land), climate, and other factors. Plants remove nutrients from the soil but return material back to the soil through roots and annual leaf fall, or plant death and decay.
To What Extent Do Humans Influence Interactions Between the Spheres?
Anyone who has flown in an airplane or spent some time using Google Earth® appreciates the amazing amount of human influence on the landscape. The intent of development is almost always to improve the human condition, but the complex chain reaction of impacts that cascade through the system can cause unintended and often harmful impacts elsewhere in one or more of the four spheres, as illustrated in the examples below. Some consequences of human impacts are not felt immediately but only appear much later, after the activity has continued for many years.
Humans clear forests, a critical part of the biosphere, to provide lumber and grow food. In addition to the loss of habitat for plants and animals, deforestation reduces the amount of CO2 that can be extracted out of the atmosphere and stored in the carbon-rich trunks, branches, and leaves of plants. Removing plant cover also causes increased runoff, which enhances soil erosion and leads to the additional loss of plant cover — an unintended consequence and a positive feedback.
Over 80,000 dams exist in the U.S., providing water supplies, generating electricity, protecting towns from flooding, and providing recreational opportunities. Dams also alter the local water balance by interrupting the normal seasonal variations in flows of water and by capturing silt, sand, wood, and other materials that would normally go downstream. Construction and filling of the reservoir disrupts ecosystems, displaces people, and threatens or destroys plant and animal communities.
Local warming of the atmosphere occurs near cities because of normal urban activities (lighting, heating, etc.) and because many urban materials, like dark asphalt, capture and store more heat than natural open space. Heat is also released from car exhausts and industrial smokestacks. Non-natural drainage systems cause rapid accumulation and channeling of water. Development infringes on natural plant and animal communities, disturbs or covers soil, and alters erosion rates.
Geography in Our Modern World
The science of geography has ancient origins, arising from the need of early civilizations for maps for navigation, planning, and other purposes. The examples above illustrate current societal issues that should also be considered from a spatial perspective — the percentage decrease in the area of rain forests, the outline of areas that will be flooded by construction of a dam, or the patterns of population growth and resulting changes in local temperatures. Understanding location and spatial distributions is as important in our modern world as it was in ancient times, because these factors are crucial in understanding the environment or determining possible sites for any human activity. For example, what spatial factors should be considered when planning a new subdivision or a new business? Geographic advantages can be the difference between success and failure, and an understanding of natural and human environments around the world is as important as ever. The map shown here depicts the average precipitation in the lower 48 states, with purple and blue designating the highest average annual precipitation, red and orange indicating the lowest precipitation, and green and yellow designating intermediate precipitation. How would you describe some of the main patterns? Where are the highest and the lowest precipitation amounts? Why are these wet or dry areas located where they are? What are some implications of the spatial distribution of high-precipitation versus low-precipitation regions? How might these variations in precipitation influence agriculture or the water supplies of the growing desert cities of the U.S. Southwest? Geographers address these and many other types of questions.