Lecture 7
Today we tried to cover geology
The Earth is a layered planet with a crust, mantle, outer core and inner core. We can access only the outermost portions of the crust (the deepest commercial oil and gas wells are about 10 km deep, whereas the crust is 5-50 km thick). We’re able to figure out what the composition of these deeper portions of the Earth are by using geophysical measurements of density and the velocity of seismic (earthquake and nuclear test) waves.
The bulk of the crust is made up of about 8 different elements with Si and O being the most abundant. Its not surprising therefore that most of the crust comprises minerals made from these two elements.
You should remember the definitions of mineral, rock, and the various rock types. In particular you should know that sedimentary rocks form from the lithification (the conversion of loose mineral material into rock) of particles transported by air, water or ice, or particles that have been chemically or biochemically precipitated from water.
Although we didn’t discuss them in detail, we referred to some of the Principles of Stratigraphy (the study of rocks as layered bodies). Among these are the law of Original Horizontality, Superposition,and Lateral Continuity. We looked at some examples of layered rocks and looked at examples of tilted sedimentary rocks. We looked at faults (normal, reverse, thrust, right-lateral, and left-lateral). You should know how to identify various types of faults.
One of the important things that we considered today was the fact that global sea-level has changed significantly over the last 600 million years. (Although the Earth is 4.5 billion years old, the last 600 million years is when most of the action occurs in terms of fossil fuel formation. When we discuss uranium resources we will find that the older rocks are quite important as well.) Just to illustrate the point I’ve added a geologic map of Nebraska and a geologic time scale for the state that I obtained from the NE State Geological Survey. You see that Nebraska was pretty much under water from the Cambrian through the Permian, exposed during the Mesozoic but submerged again in the Cretaceous. The seas receded in the latter part of the Cretaceous. Thus all continents have sedimentary rock deposited on them.
The last thing that we did was to discuss the theory of plate tectonics. The Cal-Berkeley Museum of Paleontology has a two great websites. One summarizes the Theory of Plate Tectonics and includes some excellent animations. The second covers geologic time.
Check ‘em out.
Posted: September 13th, 2009 under Study Guide, Study Guide Exam 1, Uncategorized.