geology

Explain the differences between : a disconformity and a paraconformity (b) a nonconformity and an angular unconformity

(a) At both disconformities and paraconformities the beds above and below are parallel, but at a disconformity there is clear evidence of an erosion surface (the lower layers have been eroded). (b) A nonconformity is a boundary between sedimentary rocks above and non-sedimentary rocks below while an angular unconformity is a boundary between sedimentary rocks above and tilted and eroded and sedimentary layers below.

How were mountains thought to be formed (a) by contractionists and (b) by permanentists

(a0 Contractionists assumed that mountains formed because as the Earth contracted the crust wrinkled into mountains. (b) Permanentists assumed that mountains formed by the geosynclinal process.

What are the features of a useful index fossil?

A useful index fossil must have survived for a relatively short period (e.g., around a million years), and also should have a wide distribution so that it can be used to correlate rocks from different regions.

What is an aftershock and what is the relationship between aftershocks and stress transfer?

An aftershock is any earthquake that is considered to have been caused by a previous earthquake as a result of the transfer of stress from the original earthquake.

Define the term earthquake

An earthquake is the shaking caused by the release of energy that takes place when rocks under stress within Earth break and then the two sides slide past each other.

What types of plate boundries are most likely to contribute to (a) compression, b. Extension, c. shearing

Convergent plate boundaries are the most likely to contribute to compression, divergent boundaries to extension, and transform boundaries to shearing, however all of these stress regimes can exist at any one of these boundaries.

How does elastic rebound theory help to explain how earthquakes happen?

Rocks under stress will deform elastically until they reach the point where the stored elastic energy exceeds the rock strength. At that point the rock breaks and an earthquake is produced.

3. List some of the factors that influence whether a rock will deform (in either an elastic or plastic manner) or break when placed under stress

Stronger rocks are more likely than weaker ones to deform elastically. Rock that is hot is more likely to deform plastically. Clay-bearing rocks are more likely to deform plastically when they are wet. If stress is applied quickly, the rock is more likely to break than if it is applied slowly.

List some of the evidence used by Wegener to support his idea of moving continents.

The evidence used by Wegener to support his idea of moving continents included matching continental shapes and geological features on either side of the Atlantic; common terrestrial fossils in South America, Africa, Australia, and India; and data on the rate of separation between Greenland and Europe.

What was the primary technical weakness with wegener's continental drift theory?

The primary technical weakness of Wegener's theory was that he had no realistic mechanism for making continents move.

What is a rupture surface, and how does the area of a rupture surface relate to earthquake magnitude?

The rupture surface is the surface over which there is displacement of rock during an earthquake. The magnitude of an earthquake is proportional to the area of the rupture surface and the average amount of displacement over that surface.

Explain the difference between elastic strain and plastic strain

When elastic strain takes place the rock can rebound to its original shape. When there is plastic strain the rock will be permanently deformed.

How did William Smith apply the principle of faunal succession to determine the relative ages of the sedimentary rocks of England and Wales?

William Smith was familiar with the different diagnostic fossils of the rocks of England and Wales and was able to use them to identify rocks of different ages.

A granitic rock contains inclusions (xenoliths) of basalt. What can you say about the relative ages of the granite and the basalt?

Xenoliths of basalt within a granite must be older than the granite according to the principle of inclusions.