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Material on this page is offered under a Creative Commons license unless otherwise noted below. Teaching Geoscience Online Topical Resources. What would you like to search? Finding Lab Activities Online As many us work on developing online courses we have to ask ourselves how to implement lab activities. General Exploring Earth Investigations by McDougal Littell Publishing - numerous online activities that use animations, interactive graphics, and imagery to help students gather information gleaned from lecture content Geology Lab Videos by Tom Braziunas at North Seattle Community College - students can view short video demonstrations of some of the physical geology lab activities Reynolds, et al.
Exploring Geology, 2nd Edition. The instructor DVD comes equipped with some great Google Earth exercises that would work well for online labs. In addition, it also has investigations at the end of each chapter that could be used for online labs.
Plate Tectonics Plate tectonics laboratory using plate motions 3 exercises by Richard Harwood of Black Hawk College — interactive maps showing movement relative movement of plates, are multiple choice and self-checking. Jules Verne Voyager - This is an interactive map developed by UNAVCO where students can add earthquakes, stress axes, volcanoes, or plate boundaries to the entire world or by country.
For more information on the project as well as instructions on how to use the site: Minerals Online rock and mineral identification kit by Jonathan Evenick of the University of Tennessee — provides photographs and descriptions of various rocks and minerals.
Relative age dating animation
Mineral identification and properties using photographs by Richard Harwood of Black Hawk College — students can identify minerals photographs based on mineral property choices. This site has been taken down. Contact us if you know of a suitable replacement. Searchable mineral database by Amethyst Galleries, Inc.: Students can search for minerals by class or alphabetically. Descriptions of each mineral include physical properties, crystallography information, common uses, and chemical formulas as well as pictures.
Mineral identification by Dave Jessey and Don Tarman through Cal State Pomona — students can use this site as a step-by-step tutorial to identify mineral sample. Igneous Rocks Igneous rock identification using photographs by Richard Harwood of Black Hawk College — students can identify igneous rock photographs based on rock property choices, self-checking.
Igneous rock identification by Dave Jessey and Don Tarman through Cal State Pomona — students can use this site as a step-by-step tutorial to identify igneous rock samples. Let's say we find out, through numerical dating, that the rock layer shown above is 70 million years old. We're not so sure about the next layer down, but the one below it is million years old.
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Can we tell how old this middle layer is? Not exactly, but we do know that it's somewhere between 70 and million years old. Geologists use this type of method all the time to establish relative ages of rocks. What could a geologist say about that section of rock?
Relative Geologic Dating
Following the Principle of Original Horizontality, he could say that whatever forces caused the deformation, like an earthquake, must have occurred after the formation of all the rock strata. Since we assume all the layers were originally horizontal, then anything that made them not horizontal had to have happened after the fact. We follow this same idea, with a few variations, when we talk about cross-cutting relationships in rock. Let's say, in this set of rock strata, that we found a single intrusion of igneous rock punching through the sedimentary layers.
We could assume that this igneous intrusion must have happened after the formation of the strata. If it had happened before the layers had formed, then we wouldn't see it punching through all the layers; we would only see it going through the layers that had existed at the time that it happened.
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The newer layers would have formed a cap overtop. The Principle of Cross-Cutting Relationships states that rock formations that cut across other rocks must be younger than the rocks that they cut across. The same idea applies to fault lines that slide rock layers apart from each other; a fault that cuts across a set of strata must have occurred after the formation of that set.
Geologists find the cross-cutting principle especially useful for establishing the relative ages of faults and igneous intrusions in sedimentary rocks. Sometimes, geologists find strange things inside the strata, like chunks of metamorphic or igneous rock. These items are called inclusions - foreign bodies of rock or mineral enclosed within another rock.
Because the sedimentary rock had to have formed around the object for it to be encased within the layers, geologists can establish relative dates between the inclusions and the surrounding rock. Inclusions are always older than the sedimentary rock within which they are found. Other times, geologists discover patterns in rock layers that give them confusing information. There may be a layer missing in the strata, or a set of sedimentary rock on top of metamorphic rock.
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These interfaces between discontinuous layers of rock are called unconformities. They complicate the task of relative dating, because they don't give an accurate picture of what happened in geologic history. For example, say we have a layer missing from the rock strata. That layer may have eroded away before the next layer was built upon the exposed surface. So, we'll never know what type of rock used to be there or what fossils it may have held.
One famous example of an unconformity is the Great Unconformity of the Grand Canyon. It clearly shows the interface between two types of rock: The sandstones lie horizontally, just as they did when they were originally laid down. But, the shales are all deformed and folded up.
The tops of their folds are completely gone where the sandstones have replaced them. What can we make of this giant unconformity? Can we establish any relative ages between the rock strata or the cause of their formations? Well, following the Principle of Cross-Cutting Relationships, we can tell that whatever deformed the shales - probably an earthquake - must have occurred before any of the upper sandstones were deposited.
In fact, we can put together a timeline.
Finding Lab Activities Online
The shales were deposited first, in a horizontal position, and then there was an earthquake that made them all fold up. Then, the tops were eroded off until the rock was basically flat, and then the sandstones were deposited on top of everything else. With only a few geologic principles, we've established the relative dates of all the phenomena we see in the Great Unconformity. Geologists establish the relative ages of rocks mostly through their understanding of stratigraphic succession. The Principle of Original Horizontality states that all rock layers were originally horizontal.
The Law of Superposition states that younger strata lie on top of older strata. The Principle of Cross-Cutting Relationships states that intrusions and faults that cut across rock are necessarily younger than that rock. Inclusions , or foreign bodies, found inside rock are necessarily older than that rock. And, unconformities show a discontinuity in the strata, which can only be understood by following the principles of stratigraphy. Geologists utilize all of these laws and principles to establish the relative ages of rocks and the relationships between events that occurred throughout geologic time.
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