EXAM REVIEW - THE FOURTH DIMENSION ANSWERS

What are the similarities and differences between lava and magma? Place your answer in the space below.
Similarities: Both refer to molten rock. Differences: Lava is seen at the earth's surface. Magma is inferred to be underground.
According to the chart shown below, what percentage of orthoclase does the rock with composition X-Y contain? Place your answer in the space below.
About 17 percent.

What happens to the size, shape, and diversity of sedimentary grains as they are transported? Place your answer in the space below.

They become smaller, more rounded, more well-sorted, and less diverse mineralogically.

Which classes of rocks (igneous, sedientary, metamorphic), if any, can be identified on the basis of mineralogy alone? Place your answer in the space below.

All minerals found in igneous and metamorphic rocks can also occur in sedimentary rocks. Some minerals are unique to sedimentary rocks.

What are the two meanings of the word 'crystalline'? Place your answer in the space below.

With reference to minerals: an orderly arrangement of the atoms.

With refernce to rocks: A texture of intergrown, interlocking grains.

Which classes of rocks can be crystalline? Place your answer in the space below.

Many igneous (e.g., granite), most metamorphic (e.g., marble) and some sedimentary rocks (e.g., evaporites) have crystalline textures.

How are evaporation and cooling rates related to grain size? Place your answer in the space below.

Fast rates produce small grains.

Why are vesicles likely to be associated with glass? Place your answer in the space below.

Vesicles form as gases bubble out of lavas. This happens most easily at the surface of a mass of lava. Since the cooling rate is very rapid at lava surfaces, the lava ends up being glass as atoms don't have the time to link up to form compounds (minerals).

How might oriented texture develop in an igneous rock? Place your answer in the space below.

If, when lava is erupted, the melt contains needle-shaped minerals formed in the magma chamber from which the lava came, these minerals may align themselves parallel to the direction of lava flow.

Why are folds unlikely to form at the earth's surface? Place your answer in the space below.

Folds are the result of plastic deformation. This tpe of deformation is favored by elevated temperatures most likely to be found at some depth beneath the earth's surface.

What effects does metamorphism have upon rock texture? Place your answer in the space below.

Grain size tends to increase, clastic textures to become crystalline, platy minerals to align themselves.

What geologic/geographic features are associated with colliding plates? Place your answer in the space below.

Oceanic trenches, volcanoes, earthquakes, mountain ranges.

In what year did varve layer X form? Refer to the diagram of drill cores shown below. Place your answer in the space below.

1990

After careful analysis, a geochronologist determines that an unweathered, unmetamorphosed mineral sample contains 6 trillion atoms of the radioactive element X and 18 trillion atoms of its decay product element Y. The half life of the X-Y pair is 500 million years. What is the age of the mineral sample? Place your answer in the space below.

two half lives = 1000 million years

Refer to the cross-section shown below. List the events that led to the arrangement of rocks shown in the order of their occurrence. If igneous intrusive A is 200 millions years old, intrusive B is 100 million years old. and lava flow C is 50 million years old, what is the age of layer 10? Place your answers in the space below.

See 'Unfolding The History Of The Earth - Examining a Sample of Earth History'. Layer 10 is older than 200 million years.

What is the Law of Inclusions? Place your answer in the space below.

An object included in a matrix is older than the matrix.

Should the geologist's account of the history of the earth be considered reliable? Place your answer in the space below.

Refer to 'Unfolding The History Of The Earth - Questions and Conclusions' and come to your own decision. Be prepared to provide evidence in support of your position.