Science Curriculum Preview Committee Clarification of Learning Results

Curriculum Organizing Questions	How old is the earth? Has the earth always been the same as it is now? How can we tell? How can scientists measure the age of the earth?
Elaboration	Students have difficulty grasping the span of geologic time, and teachers must take this into account when discussing the age of the earth. At the 5-8 level, discussions of the age of the earth will be descriptive and introductory. Students need to be exposed to the idea of sedimentation, fossils and carbon dating. They should also be introduced to short and long term processes that change landforms such as earthquakes, volcanoes, weathering and erosion.
Specific Ideas	Some changes in the earth's surface are abrupt (such as earthquakes and volcanic eruptions) while other changes happen very slowly (such as uplift and wearing down of mountains). The earth's surface is shaped in part by the motion of water and wind over long times, which acts to level mountain ranges. Benchmarks 4C Thousands of layers of sedimentary rock confirm the long history of the changin surface of the earth and the changing surface of he earth and the changing life forms who remains are found in successive layers. The youngest layers are not always found on tip, because of folding, breaking, and uplift of layers. Benchmarks 4C Geologic time can be estimated by observing rock sequences and using fossils to correlate the sequences at various locations. currrent methods include using the known decay rates of radioactive isotopes present in rocks to measure the time since the rock was formed. NSES 5-8D3b
Developmental & Instructional Implications	Many of the national standards for this concept are 9-12. Teachers of 5-8 should view their teaching of this topic as an introduction. Teachers should also be sensitive to students whose religious beliefs include creationism. Change in the conception of the age of the earth - from a few thousand to many millions of years -- proposed by scientists in the 1800s was dramatic, and for most pople beyond belief. The estimated age wes unimaginably greater than the prevailing beliefs. It was also based on the assumption that the earth's features (mountains, valleys, etc.) had been formed gradually by processes still underway, not in a single, instantaneous creation. People have difficulty imaging time spans that are vastly longer than human experience. In overturning the "sensible' notion that the earth is at most only a few thousand years old, science understandably provoked substantial opposition. The new theory was based on indirect evidence from fossils and rock formations and supported the even less acceptable concept of biologicical evolution. Benchmarks p. 246 It is especially important that students come to understand how sedimentary rock is formed periodically, embedding plant and animal remains and leaving a record of the sequence in which the plants and animals appeared and disappeared. Besides the relative age of the rock layers, the absolute age of those remains is central to the argument that there has been enough time for evolution of species. The process of sedimentation is understandable and observable. But imagining the span of geologic time will be difficult for students. Benchmarks p. 73 Students of all ages may hold the view that the world was always as it is now, or that any changes that have occurred must have been sudden and comprehensive. Moreover, middle-school students taught by traditional means are not able to construct coherent explanatons about he causes of volcanoes and earthquakes. Benchmarks p. 50
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