1986

We realize an Earth science program such as we describe does not exist except in this paper and in the minds of Earth science teachers who strive to develop an exemplary Earth science program, we cannot ignore fundamental components. Therefore, our paper includes discussions on the major unifying themes of Earth science, the recognition of recent advances in Earth science disciplines, and the traditional goals of Earth science education. Unifying Themes While many themes underlie the study of Earth science, some play a more unifying role than others. Our intention is to suggest major areas that encompass the concepts and processes essential to any Earth science program. Change Understanding the dimensions, processes, and rates and directions of past and predicted change is basic to education in the Earth sciences. Cycles Understanding the dimensions, processes, and rates and directions of past and predicted change is basic to education in the Earth sciences. Cycles The cyclic nature of some changes is an extension of change as a major theme. Examples include the concepts and processes of the rock cycle and hydrologic cycle. Equilibrium Earth systems tend to change, use, or dissipate energy toward a state of equilibrium or balance. This theme applies to such diverse studies as temperature changes, erosion, and weather. Energy Changes and cycles occur through the redistribution of energy. The origin, use, and dissipation (en:ropy) of energy in Earth systems is a theme that unites diverse disciplines of Earth science. Conservation The total amount of matter and energy in Earth, solar, and universal systems remains essentially constant. Interactions among Earth and solar systems may change and redistribute matter and energy, but the total amount of each does not change. Scale Any aspect of Earth science requires students comprehend dimensions of space and time. Events, changes, and cycles in Earth systems occur along a continuum of very short (microseconds) to very long (geological eras) time spans, and of very small (atomic molecules to very large (continents) sizes. Study in Earth science should in student comprehension of the scale of events in space and time. Resource Finiteness The Earth's useful resources are finite and unevenly distributed. Recognition of these limitations means decisions relative to resource use must be made. The theme of finiteness stands as an important new unifying theme in the Earth sciences. Interdisciplinary Nature In order to understand nature and the many problems confronting humanity it is necessary to understand and analyze the Earth from an interdisciplinary perspective. Although Earth science is, by definition, already an interdisciplinary study, this theme must become more important in coming decades. Process Uniformity Fundamental physical, chemical, and biological processes operating today are the same as those References Barney, C.

1996

The mid-ocean spreading centers that host the hydrothermal vents and chemosynthetic organisms consist of a continuous string of volcanoes that encircle the globe . This mid-ocean ridge system produces new sea floor when the volcanoes erupt. Lava pours onto the sea floor, cools and spreads away from the ridge crest to become the conveyor belt upon which the continents ride, hence the name seafloor spreading. This process forms new ocean floor, then moves this new lava away from the mountain crest as ever newer lava replaces it.

In the Geological studies there are several field maps that are available to know the ground features and various geological parameters, but if the tectonic stress directions are measured at various available places and marked globally on a world map then it is called World Stress Map (WSM). These stress directions are helpful not only for academic research but also for compiling the vast data on a global scale to know the geodynamics and plate movement. The world stress map shows the orientations of Maximum Principal Horizontal Stress Direction measured at various places in different countries. There are two types of stresses available based on the regional and local scales. Regional stresses are also called first order estimates which are based on the measurements of earth quake focal mechanism studies at the particular site globally or regionally. But the second order stresses are completely local parameters generally carried out for specific engineering purpose. To prepare the world stress map the first order stresses are very important and generally incorporated in the world stress map and the less importance is given for second order stress, since these measurements are most of the times determined at shallow depths and are not reliable indicators to include in the stress map. However the first and second order stress directions are mapped on the world stress map to know the possible global phenomenon like plate dynamics. The world stress map is being prepared and updated periodically by WSM project. The 1992 version of the World Stress Map was derived mainly from geological observations on earthquake focal mechanisms, volcanic alignments and fault slip interpretations. Less than 5% of the data was based upon hydraulic fracturing or overcoring measurements of the type commonly used in mining and civil engineering projects. The 2005 version of world stress map shows the huge number of data collected from hydrofracturing, overcoring, borehole breakout etc.

The fast development of a network of permanent stations as well as the enhancement of capabilities and resolution of portable GPS receivers facilitates the accumulation of information on earth's surface displacement and opens up new possibilities for modeling geodynamic processes based on geodesic data.

These same ancient shallow seas sometimes allowed large areas to become isolated and begin drying up. In that setting, as the seawater grows more concentrated, minerals begin to come out of solution (precipitate), starting with calcite, then gypsum, then halite. The resulting rocks are certain limestones or dolomites, gypsum rock, and rock salt respectively. These rocks, called the evaporite sequence, are also part of the sedimentary clan. In some cases chert can also form by precipitation. This usually happens below the sediment surface, where different fluids can circulate and interact chemically.