The Physical Earth

"Piecing Continents Together"...88
"A Mountain"...90
Sulfur plumes off Namibia...93
Four False Color Views of Ocean Surface Height of the Pacific Ocean...95
"Low Ozone Level Found Above Antarctica"...98
"A Semidesert with a Desert Heart"...100
"At Last, the Smoking Gun?"...104
Fires Raging Across Indonesia...107
"The Torino Impact Hazard Scale"...109
Climate Change Impacts on the United States...114
"The New View of Natural Climate Variation"...118
Dust Cloud over Japan...121
Holes in Ozone Layer of Earth...123
Earth Story...125
Water Resources of the United States...128
WMO Statement on the Status of the Global Climate in 2004...130
"Shrinking Glaciers Evidence of Global Warming: Differences Seen by Looking at Photos From 100 Years Ago"...133
The Seasons and the Earth's Orbit...135
"Global Warming: The Culprit? Evidence mounts that human activity is helping fuel these monster hurricanes"...139

The physical Earth refers to all of the features of Earth except those that are living. Often the physical Earth is subdivided into three spheres: the geosphere, the hydrosphere, and the atmosphere. The geosphere includes all of the mineral components of the planet, such as soil, rock, sand, and clay. The hydrosphere refers to all water on the planet, including liquid water (both fresh and saline), water vapor, and ice. The atmosphere is the gaseous material that surrounds the planet.

The physical Earth also refers to the climatological characteristics of the planet. This includes temperature and weather patterns. Because the Earth is a sphere, heat is concentrated near the equator and is more diffuse near the poles. The average temperature varies greatly with latitude (i.e., the distance from the equator).

Precipitation patterns on Earth are also greatly influenced by latitude. Equatorial heating evaporates water, which rises into the atmosphere. There, the air cools and water vapors condense bringing rains to tropical regions. At about 86°F (30°C), warm dry air subsides from the atmosphere, driving the trade winds and creating large swaths of desert regions.

The climate is not a predictable feature, but rather an extremely dynamic process. Seasonal variations in the tilt of Earth as well as Earth's position with respect to the sun contribute to variability in climate. Altitude is another controlling factor. Finally, the atmosphere plays a key role, acting as a thermal insulator and as a heat valve for the planet.

The various components of the physical Earth are often referred to as natural resources by ecologists and environmental scientists. To survive, all organisms depend on the geosphere, the hydrosphere, and the atmosphere. The climate is also of great importance to ecosystems. Since the mid-1900s, the human population of the planet has exploded, making human beings the dominant species on the planet. People's activities place heavy demands on the physical resources of Earth. This strains the natural resources of the planet. Mining and urban development have changed the physical landscape. Pollutants have clogged waterways. The burning of fossil fuels has polluted the atmosphere. Evidence continues to accumulate that increased carbon dioxide in the air has contributed to a rise in global temperatures.

The ecological effects of damaging the physical Earth can be severe. For example, in the 1930s in the American Southwest, domesticated animals were allowed to graze heavily in desert areas. This, in combination with an unusually long drought, converted the physical environment into a dust bowl—a vast wasteland. Dust storms became ubiquitous. The dust bowl was a great economic disaster, displacing hundreds of thousands of farmers. Native species were unable to recolonize the land for several decades.

In the early 2000s in Alaska, photographs document that glaciers are shrinking, most likely due to increased annual average temperatures. This chapter explores the events that contributed to the dust bowl and the shrinking glaciers in the Arctic, as well as other ecological threats to the physical Earth.