As you prepare for your first exam in Dynamic Earth, remember that most of the questions will be multiple choice format. Questions will either have four or five possible answers from which to choose. And only one choice will be correct, unlike in our warm-ups.

It would be a huge mistake for you to try to prepare by simply memorizing answers. Rather, you should ask yourself lots of questions so that the questions I ask will not be unfamiliar. Use the warm-ups as a guide.

But remember, the warm-ups are meant to get you thinking about the important points in the reading and in the lecture/discussion sessions. They are not meant to provide examples of all the questions you might be asked. The ultimate responsibility for adequate learning and preparation rests with you, the student! So go beyond the specific questions in the warm-ups and read the material in a critical way. Ask yourself plenty of questions, and attempt to answer them by appropriate reasoning.

Generally, there are two types of questions that may be asked. One type of question relies mainly on memory of definitions. These questions will be in the minority! The other requires you to link two or more ideas together in order to reach the best conclusion. When you take the exam, read the questions carefully, then compare each of the possible answers to the question in order to make the best choice. Here are several example of what I mean, taken from the area of ineous rocks.

Question:

A porphyritic texture is

• (a) uniformly finely crystalline
• (b) uniformly coarsely crystalline
• (c) not visible to the naked eye
• (d) made of aphanitic groundmass with easily visible phenocrysts

Notice that this question maily relies on your knowledge of the definition of porphyritic texture. It only requires that you learn that a porphyritic texture consists of an aphanitic groundmass with easily visible phenocrysts. The answer of course is (d).

Question

A porphyritic texture forms when

• (a) a magma cools slowly at great depths beneath the earth's surface
• (b) lava is erupted at the surface, and the entire flow cools very quickly
• (c) a magma cools slowly at depth, then is erupted at the surface and completes its solidification rapidly
• (d) cooling takes place so rapidly that no crystals form, whether visible or invisible

In this question, it is assumed that you know that a porphyritic texture consists of a groundmass of invisible crystals, with phenocrysts of easily visible crystals. The question goes beyond this definition, and also assumes that you understand the reasons why different crystal sizes form from molten material. The questions also requires you to know how the control on texture is related to the place where the magma (or lava) solidifies.

Linking all these things together, the thoughtful student will recognize that cooling rate is a prime control in determining crystal size. And this same student will recognize that slow cooling forms large crystals, rapid cooling forms small crystals or even glass. Finally, the student will recognize that slow cooling takes place at depth, and rapid cooling takes place at the surface. Putting these links of reasoning together, the student will arrive at (c) as the answer.