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Natural Science - Year II

Unit 40: Basic Geology

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Science Web Assignment for Unit 40

This Unit's Homework Page History Lecture Science Lecture Lab Parents' Notes

Science Lecture for Unit 40: Basic Geological Principles of Formation and Erosion

For Class


Rocks and minerals

The first thing you notice about rocks is that there is an enormous variety, making them hard to hard to identify. Modern rock classification puts chunks of solid not-just-dirt clod stuff into two groups: minerals, which are usually single elements or simple molecules in pure form, and rocks, which are mixtures of minerals. Rocks themselves are divided into three groups, based on the processes that formed them. Can you determine to which class each of the rocks below belongs?

Rock Collection


Sandstone. Notice the stratification. This specimen has been "polished" by tumbling in a river, but remains a good example of sedimentary rock. /td>

Copper Ore


Copper ore. The blue-green streaks are characteristic of copper oxides, like malachite, the result of recombination of materials under extreme pressure and heat — the result of metamorphic changes.



Pumice. Full of holes and light enough to float on water, this is the result of a volcanic eruption — igneous rock.

Forces building up the earth

The classification system points out the contrary forces at work on the surface of the earth. Vulcanism and sedimentation build up the surface; weathering by wind and water pulls it down (so both the Vulcanists and Neptunists were right in a way). Let's first consider the "building up" forces:

Examples of geological events

Four Cascade Volcanoes

Read through the description of sea-floor spreading and plate movement at the USGS site on the North Cascades. Be sure to click on the animations (there are two).

  • What phenomena are used to map the movement of different parts of the ocean floor?
  • Why would horizontal stripes of reversing polarity on the ocean floor map to vertical layers on land?
  • What is lithosphere?
  • How does upwelling in seafloor spreading form new crust material?
  • What is a transform boundary?
  • Why is the earth considered "geologically active"?

Forces of Erosion: weather

In contrast to the building forces coming from the earth's interior, weathering tears down the mountains and erodes the plains. While wind can carve interesting shapes, it is water which does the most sculpting, as rivers cut through plains, oceans eat away at the coastlines, and ice breaks apart rocks bit by bit each winter or, as glaciers, carves whole valleys out.

Read the brief outline on the forces and effects of erosion at the Georgia Perimeter College Earth Science site.

  • What are the major forces of erosion? Do you think this list is complete?
  • How does water both build up and tear down the earth's surface?
  • How does wind both build up and tear down the earth's surface?
  • What is "mass wasting"? How does it build up and tear down the earth's surface?

Study/Discussion Questions

Further Study On your Own (Optional)