Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards

Density Studies of the Earth

Convection in Earth’s Mantle, Atmosphere, and Oceans: their Sources and Effects
The outward transfer of earth’s internal heat drives convection circulation in the mantle that propels the plates comprising earth’s surface across the face of the globe.

Heating of earth’s surface and atmosphere by the sun drives convection within the atmosphere and oceans, producing winds and ocean currents.

Further Description:

There are two vastly different kinds of heat transformation systems. In the Earth, the amount of heat on the average is very small relative to that from the sun. The processes inside Earth are also mostly very slow, some requiring thousands to millions of years. Others, like volcanoes and earthquakes, require months to hundreds of years for any given location. The sun’s energy absorbed and reradiated by Earth, which provides heat to interact with the oceans and atmosphere, involves transformations that occur much more rapidly than those inside Earth. Also, the total amount of energy from the sun is far greater.

Energy from the sun powers many of the gigantic cycles found on Earth. One of these is the hydrologic cycle, which provides a continuous exchange of water between the oceans, the atmosphere, and the continents. The energy from the sun also creates pressure and temperature differences on Earth’s surface that, in turn, produce winds. Large-scale global wind patterns are a result of this interaction. These winds provide the energy for the production of surface waves and ocean currents. Small-scale wind patterns such as land and sea breezes are also connected with differential heating and resulting variations in pressure.

Storms such as hurricanes draw on this energy stored in the oceans. A hurricane’s wind patterns and development progress through a series of stages. Winds become more organized in their cyclonic pattern and grow stronger. The hurricane moves across the earth’s surface in response to pressure differences, as latent heat released during condensation drives the storm. The warm ocean provides the water vapor. Once on land a hurricane quickly dissipates because its source of energy is no longer available.

The physical movements of the ocean, such as currents and waves, can be studied to show the connection between the wind and these movements. Buffering of various substances also is affected by changes in the hydrosphere. Evaporation and indirect effects of wind change certain concentrations. Marine life also is affected by these winds, movements, and chemical buffering. Due to their mode of living, organisms are found in certain oceanic habitats.

Seismic waves are the major mechanism by which Earth’s interior can be examined. Such waves can be interpreted in terms of refraction, reflection, wave speed, dispersion, and diffraction. From these wave properties, inferences of seismic disturbances provide a wealth of data about Earth’s interior.

Seismic studies of the interior of the earth support the existence of "plastic" areas that allow convection movements. These plastic areas, although still solid, would be hot enough to flow in the typical circular pattern. Harry Hess (1960s) proposed that these convection cells acted as conveyor belts. Material rising at the ridges moves toward the trenches, carrying the sea floor with it. This model is supported by the relative youthfulness of the oceanic crust at the ridges as compared to its age in the trenches. Paleomagnetism studies further support this hypothesis.

The theory of plate tectonics provides a way to explain the earth’s internal behavior, including patterns of earthquakes, faults and volcanoes on the earth’s surface. Oceanic features such as the ridges, trenches, sea mounts, and rift valleys also are seen to have important functions on the surface. Igneous rocks of various types (FeMg silicates) can be identified and provide clues to the movement and existence of plates.

Concepts Needed:

Grade 9

Convection, speed and wave speed, wavelength, period, frequency, s (transverse) and P (longitudinal) waves, refraction, reflection, sea waves

Grade 10

Convection, subduction, plate boundaries, continent, ocean basin, rift zone, midocean ridge, volcanoes, earthquakes, faults, brittle, plastic, transform, trailing edge, collision edge, continental drift, plate tectonics, barometer, barometric pressure, isobars, temperature, precipitation, climate zones, global wind patterns, humidity, condensation, evaporation, transpiration, air masses, fronts, storms, inclination, rotation

Grade 11

Lithosphere, asthenosphere, Moho discontinuity, basalt, granite, andesite, viscosity, isostacy, paleomagnetism, sediments, subduction, ocean bottom structure

Grade 12

High pressure, low pressure, cyclones, hurricanes, currents, fronts

Empirical Laws or Observed Relationships:

Convection of solids, plasticity of solids, partial melting, conservation of energy, formation of currents, seismic transmission, reflection and refraction, continental drift

Theories or Models:

Theory of hurricane development, plate tectonics, gravity, origin and early history of Earth, models of Earth=s interior structure and composition

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Micro-Unit Description:

Density Studies of the Earth
Students should determine the mass and volume of solids, liquids, and gases and develop the concept of density as a characteristic property. They should distinguish pure substances from mixtures as matter that has a single set of characteristic properties, including boiling point, freezing point, density, solubility, viscosity, and conductivity. (b) Much of the evidence supporting plate tectonics is connected to other areas of science. Some density studies could be conducted in grade nine to support later development of the model of Earth's interior.

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