Lesson+Quiz+Week+1

=Thank You For Filling Out This Form= Below is what you submitted to dl@pisgahforestinstitute.org on Sunday, February 24, 2008 at 19:13:15


 * Name:** Kim Collazo
 * E-mail:** kscollazo@gmail.com
 * Question 1:** The epoch is the more specific geologic time.
 * Question 2 :** The significant geologic event that divides the Cretaceous and Tertiary is the mass extinction of the dinosaurs (excluding birds).
 * Question 3:** A half-life is the quantity of time it takes an isotope to decay to half of its initial value. It is used in dating rocks by following these steps: 1. Find the ratio of parent to daughter isotope in the rock you are trying to date. 2. Know the 1/2 life value of the parent isotope (ie. Carbon-14 = 5730y). 3. Calculate the number of 1/2 lives that have occurred. 4. Multiply the number of 1/2 lives by the number of years per 1/2 life. This process is known as radiometric dating.
 * Question 4:** The law of cross-cutting relationships refers to the idea that a rock is older than any rock that cuts across it. This is due to magma that may have intruded into older rock, and created new rock. These are known as igneous intrusions and are always younger than the surrounding rock. This could also be caused by igneous extrusions in which lava on the surface forms rock that is younger than the rock it covers.
 * Question 5:** A trace fossil is evidence of an organisms existence in an area. It may not include actual elements of the organism, but provides evidence that the organism was there.
 * Question 6:** The current theory regarding plate movement involves the convection currents that flow through the lower semi-solid mantle (asthenosphere). It is believed that this slow flowing material heats due to the heat of Earth's core, rises, cools, and sinks continually. This motion causes the floating plates above to move.
 * Question 7:** Divergent plate boundaries are mainly found under the oceans where two plates are moving away from each other due to the motion of the convection currents under them. The most impressive divergent boundary is that of the Mid-Atlantic Ridge in which sea floor spreading can be dramatically studied. Although not all divergence is occurring under the ocean as demonstrated across the land of Iceland.
 * Question 8:** The Hawaiian Islands were formed as the thin ocean crust they were born from "floated" over what is known as a hot spot. Although not located near any plate boundaries, the heat of the magma below this weak crust, caused cracks and openings to emerge through which the molten material was able to ooze through creating the islands of Hawaii.
 * Question 9:** The Earth's polarity has not always been the same. This has been proven through "magnetic striping". Rocks can be grouped as having normal polarity (having the same polarity as Earth's present magnetic field) or reversed polarity (alignment opposite of present Earth). During seafloor mapping stripes of rock running parallel to ridge crests were found to have alternating polarity, suggesting that Earth's magnetic field has flip-flopped many times throughout history.
 * Question 10:** Continental plates seem to "float" better than oceanic plates because they are composed mainly of granite (quartz and feldspar) which are relatively lightweight compared to the much denser and heavier basalt which makes up the oceanic crust.
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