AboutC. Robert Reszka, Jr. Expertise I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.
Experience I have been working for the State of Michigan for 24 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.
Organizations Michigan Basin Geological Society
Publications Decade of North American Geology.
Bedrock Geology of Michigan
I have taken courses in geology but have always had a problem visualizing "polar wandering." Do you have a simple way of explaining it? Looking at maps with polar wandering trails is confusing.
Answer Hi Joe,
“Polar wandering” is kind of a misnomer, well, at least it was until about the year 2000. Let me explain. You know about continental drift. Do you know that magnetic minerals will align with the Earth's magnetic lines when they are floating in a magma? So….we have molten rock with magnetic minerals in it. The magnetic minerals float around freely and respond to the magnetic force of the Earth; think iron filings and a bar magnet. The magma cools and hardens, freezing the magnetic minerals into the position they were pushed into by the magnetic fields. Ok….so now we have rocks with minerals, whose magnetic orientation we can measure. We look at lots of these minerals within the rock and figure out their orientation.
Many times they are not oriented in the same direction as the current magnetic field of the Earth. When the rocks lithified the minerals were aligned with the magnetic field. Now they are not. That can only mean that something has moved. Plate tectonics tells us that the continental plates moved over geologic time. That movement caused a misalignment of the minerals.
So…it's not really that the poles moved it's that the continents did. We can study the orientation of the minerals and infer where the poles were when the rock was lithified. We can then run time back, moving the continents at the same time, and deduce where they were, at least in that location, when the rock hardened.
Saying “polar wandering” is kind of like saying “the sun is rising”. The sun doesn't “rise”, it just looks like it. The more proper term should be “apparent polar wandering”.
This is not an easy concept and the various maps don't make it easy. Some maps have curves that indicate how the continents moved through time. Others show a meridian and a circle that's meant to show the location of the pole in relation to the equator. Neither is intuitive. The best help I can give is to start thinking of the plates as moving, all in relation to each other. Don't try to figure the correct motions yet. Just feel that they are in motion and tie that motion to the north magnetic pole. Not easy I know but it helps me to mentally draw a line from the point in question to the pole and swing it around. Just takes practice.
Ok, there's a problem here though. This was accepted until 2000 when a paper was published in “Science” that showed that about 84 million years ago the pole actually did move. The mechanism is not known, lots of speculation though. This adds a little mud to the not so clear water but most of the maps you will see are drawn to show the movement of tectonic plates in relation to a stationary pole. On the whole they are correct since it appears the poles moved only that one time. We can't ignore that movement but we can assume most “apparent polar wandering” is due to the movement of the continental land masses.
Here are a couple of sites that you might find interesting:
