1] Compare and contrast relative age dating with radiometric dating. What are the strengths and limitations (if any) of each?

Before radiometric dating (also known as carbon dating), relative age dating was used, and it was primarily educated guesswork that did not have a scientific basis and lent itself to individual bias. After using this inaccurate method, scientists began to look at the different archaeological strata or layers of earth and use a comparison type method based on the idea that the earths geological layers are oldest at the bottom and that “an object cannot be older than the materials of which it is composed” (Dating, paragraph 2). The age of objects can then be determined by comparing the object’s relative position in the layers to other known items. Items that are in the same layer will be the same relative age. This method of dating is not always reliable as some materials may not deteriorate at a predicted rate, or may be protected by some situation from usual deterioration with the other objects in the same strata. For example, if something is inside something else that protects the item from natural deterioration there will be inaccuracies.

Radiometric dating, however, uses the scientific method of comparing radioactive isotopes which are found naturally in the rocks to the amount of natural decay in an item to determine the date of a various strata. Scientists have found that these isotopes change, or decay into non-radioactive elements at a constant rate (known as half-life). While these methods are not scientifically testable, they are generally reliable.
2] Volcanoes are generally not preserved in the geologic rock record as they are usually eroded away. However, the various materials erupted from volcanoes are often found preserved in the rock record. From what you have learned about the different types of volcanoes, how could you infer what type of volcano erupted in a given area based on the type of volcanic deposits now found as layers of rock? Give specific examples, and briefly discuss how some materials may be linked to different types of volcanoes

It is of interest to estimate both the type and date of volcanic eruptions. Looking at the layers of younger lava deposits and their characteristics may help to decide the type of volcano which caused the lava flow and holds the remains of plant and/or animal life.

It might be possible to determine dates of lava flow through comparison dating or radiometric dating and therefore determine historically what type of volcanic eruption happened when compared with other geological events occurring at the same time.

Since the most common volcano, the composite or strato volcano is formed by alternating layers of lava and rock fragments (Composite Volcanoes, n.d., paragraph 1) the identity of the type of volcano may be determined by looking at the composition of the lava flow. Strato volcanoes can be determined by “half-half lava and pyroclastic material” (Strato Volcanoes, paragraph 1). The strata are composed of ash layers and lava flow.If the composition of the lava is largely basalt, and not deep, then the volcano may have been a shield volcano.

Scientists may investigate the layers of the youngest deposits as well as the form and structure of any plant life trapped in the lava flows and use comparative dating to determine not only the date, but the type of volcanic activity. If material is trapped inside layers of very thick rock, it is possible to determine type of eruption by the speed of flow.

3]When examining the geology of a region for potential useable aquifers, what characteristics or factors would you consider? Also, taking into account certain natural and human factors, which areas would you avoid?

An aquifer is the name given to“underground soil or rock through which ground water can easily move” (What is Ground Water? n.d., paragraph 5). The amount of ground water that can flow through soil or rock depends on the size of the spaces in the soil or rock and how well the spaces are connected. The amount of spaces is the porosity. Permeability is a measure of how well the spaces are connected. It is desirable to have good porosity and permeability.

It is crucial to know the quality of certain factors of useable aquifers in order to establish the quality and potential of the available potable water in an area. Therefore we would look for environmental factors that would indicate good porosity and permeability. Porosity tells how much water the aquifer can store.

To establish the connection of the pore spaces, it would be necessary to look at the characteristics of the water table. Poor spaces need to be connected (Aquifer Characteristics, n.d.). Slope is an important factor to know how quickly the water will flow downwards. Speedy downward flow is not a good indicator due to the fine sediment that can be carried in this flow.

Permeability tells us if the smaller grains of material will decrease the porosity making the aquifer less permeable and less desirable. The types of rock which make up the sediment are also important as to whether there will be waste (too much sediment on a downward slope).

It is also important to look at the surrounding climate to see what types of weathering exist to breakdown the bedrock. If it is too severe, there will be too much sediment. High rainfall generally leads to better chances for good aquifers.

Unfortunately man has introduced a good deal of ground water contamination, whether it is chemical deposits or animal overuse. Other environmental concerns are avoidance of areas with high evaporation rates or connections to areas with high saline concentration.

4]Wind is included along with gravity, water, and ice as an agent of erosion. In many areas of natural beauty, statements are often made that credit wind as having sculpted the landscape. Briefly discuss the importance of wind as an agent of erosion, and explain why such statements are probably inaccurate.

Wind power seems to be an obvious explanation for the erosion of rock eventually forming a sculpted landscape. However, even wind forces as great as a hurricane or tornado do not re-form the landscape. Wind is an erosive agent in flat areas such as grassland or the deserts because the soil is loose or sandy and can be easily blown away to form sand type sculptures. As the wind blows away the topsoil, a new layer of topsoil is revealed, even poorer than the previous one, and easier to “sculpt” by the wind or other erosive agents. Hard packed dirt or rock formations are not easily changed by wind forces but also need temperature changes to alter their shape or some type of abrasive force such as particles of dirt which can do the sculpting. Without the particles within the wind, the wind is actually quite smooth and has very little erosion power. Wind has little power to attack solid rock (Dutch, 2009). One exception would be if a rock formation had some layers which were softer than others. The wind can erode the softer part of the rock and leave behind the more resistant part of the rock.

Water, in various states is much more effective in changing the face of the landscape. When frozen water lodges in the cracks of rocks, pieces can break off changing the shape of a rock formation.

5]How are faults, foci (plural of focus), and epicenters related? Faults that are experiencing no active creep (relatively consistent yet minor movements) may be considered “safe.” Rebut or defend this statement with what you have learned so far about faults.

Faults are fractures in the earth’s crust. Typically earthquakes occur along known fault lines. A focus for an earthquake event is where the earthquake begins. There may be more than one focus, in which case they are called foci. The earthquake’s fracturing must begin at a focus. An earthquake occurs when there is a release of energy which occurs at the focus point.

Both fault lines and the foci are inside the earth’s crust and not on top of the surface. In order to pinpoint or visualize where a focus has occurred, we use a point directly above the fault’s focus point on the surface of the earth. This is called an epicenter and helps humans to locate where the beginning of the earthquake was.

Active creep does not indicate either safety or danger for faults which cause earthquakes. A fault creep happens when there is constant stress over a prolonged period of time. The stress causes the rocks to begin to slowly move. As the rock movement progresses, slippage occurs and there may be a small earthquake. An active creep zone may just mean that a large number of displacements have occurred, but they do not develop into earthquakes.This does not always occur, and slippage may not bring any event on. Conversely, a lack of or weakness in activerock creep does not mean there won’t be an earthquake.

6]How were earthquake intensities measured before the advent of the Richter scale? What were the problems with that scale, and how is the Richter scale far superior?

Before the Richter scale, a scale called the Mercalli Intensity Scale was used which measured the shaking of an earthquake on a scale from 1 to 12. Prior to that the Rossi-Forel scale was used. The Mercalli scale measured the effects of the intensity of an earthquake through observation. It did not measure the amount of energy involved, and it did not measure accurately depending on depth or distance of the earthquake. Thus earthquakes which had similar distances from epicenters were given the same rating even if one had expended a greater amount of energy. Another lack of scientific accuracy was that it is possible for two earthquakes of similar magnitude can occur but because they were located at different depths exhibiting different visual effects they would be given different Mercalli numbers.

The Richter scale uses instruments to measure the energy of an earthquake. It was found that simple visual observations of ground shaking do not give a great deal of scientific information with regard to the more important measurable circumstance of energy release nor is it accurate. Destructive power based on personal observation is more dramatic, but less descriptive for scientific purposes.

The energy released is more important in correlating the destructive power. This is a more scientific approach.

The Richter Scale uses powers of 10 to measuremagnitude which allows for a greater range of descriptive terms for the energy release. In this way, for example, a 5 magnitude earthquake is 100 times (of 102) stronger than a 3 magnitude earthquake.

References

Aquifer Characteristics, (n.d.). Retrieved February 2013 from

Composite Volcanoes, (n.d.). Retrieved March 2013 from

Dating: Relative Dating, (n.d.). Retrieved March 2013 from

Dutch, Steven, Wind Erosion, (December 14, 2009). Retrieved February 2013 from

Strato volcanoes, (n.d.). Retrieved March 2013 from

What is Ground Water? (n.d.). Retrieved March 2013 from