The New Dictionary of Cultural Literacy, Third Edition. 2002.
Earth Sciences
The central problem of the Earth sciences is to understand how our planet works and how it came to be the way it is. The essential fact emerging from these sciences is that the Earth can be pictured as a set of three separate but interconnected cycles.
The geological cycle governs the formation and disappearance of solid land. The science of geology contains two central insights. The first of these, arrived at in the eighteenth century, is that the Earth is very old and that its history can be read in the rocks on its surface. The second insight, gained in the late 1960s, is that the Earth has evolved and continues to do so. The continents have not always been where they are now, nor have they always had their present shape. Instead, the surface of the Earth has changed constantly, and the continents have moved about, sometimes breaking up into pieces, sometimes coming together again. This picture of the Earth, called plate tectonics, replaced the old idea of a static and unchanging planet. The study of the rocks and their history is the subject of geology, whereas the study of the forces that drive the activity on the surface is part of the newer field of geophysics.
At the same time that the continents are moving, a smaller-scale geological cycle, involving the formation of rocks and their erosion into sediments and soil, goes on. In river deltas and the eruption of volcanoes, new land surface is added to the Earth. At the same time, the inexorable forces of weather and time break down the mountains.
On the stage set by motion of the continents, the atmospheric cycle operates. Powered by heat from the sun and the Earth’s rotation, winds move across the surface, carrying weather systems. Rainfall, temperatures, and other day-to-day aspects of our environment change in response to the prevailing winds and the jet streams. These weather patterns and their causes are the subject of the science of meteorology.
Over longer time periods, changes in the Earth’s orbit or movement of the continents alter the patterns followed by the winds and the temperatures on the Earth. Such changes in climate, of which the recurring ice ages are a good example, have had a profound effect on the development of the human race. Understanding long-term climate development is one of the major research fields in the Earth sciences.
Intermediate between the slow, majestic changes in the continents and the daily changes in the weather is the third great cycle—the hydrologic cycle, the cycle of the Earth’s water, or hydrosphere. Water evaporates from the surface and returns as rain or snow. Some water is locked up in the polar ice caps, but most resides in the oceans. Perhaps the most poorly understood part of our planet, the oceans act as a great reservoir for many natural and artificial substances. Their currents help equalize temperatures on the globe, while at the same time they spawn the major storm systems that have such an important effect on human activities.
The entries in this section were chosen according to slightly different criteria from those used in the humanities and social sciences sections. They were chosen not because the majority of educated readers are expected to be familiar with them, but because most scientists would agree that they are essential to a knowledge of the Earth sciences. Some of these words might be used without explanation in the New York Times, but many would not. Nevertheless, if you are familiar with these terms and the concepts they represent, you should know enough about the study of the Earth, the oceans, and the weather to follow their progress as it is presented in the popular press.
