Apparent Polar Wandering?

Buffy · 09-12-2005

Quote:

Originally Posted by Turtle

This is not the case as I understand it. The theory which has a large body striking Earth & forming the Moon, also allows for the impact altering Earth's axis in relation to the Sun (curently approx. 23 1/2 degrees).

Well you're quite right Turtle. I should have said, "since we last got whacked with a moon/mars size object"... Since then of course there's been lotso shifting of continents and occasional bobbles due to minor impacts (like the ones 250mya and 65mya) that have had a bit of a shift, but I'll tell ya, changing the angular momentum of a mass the size of the Earth is really hard!

You-say-you-want-a-revolution,
Buffy

kingwinner · 09-16-2005

I found out from the web that there are 3 types of polar wander: apparent polar wander, magnetic polar wander, true polar wander. And the true polar wander means the migration of the geographic poles.
Magnetic polar wander is the accurate movement of the magnetic poles with respect to the geographic poles (when the geographic poles are considered stationary)

kingwinner · 09-16-2005

"In the past, the geologists examining ancient rocks (paleomagnetism) assumed the continents did not move so the magnetic north pole APPEARED to be moved, hence this is called apparent polar wander.
When the continents are considered to be moving (RATHER THAN THE POLE), the PATHWAYS correspond."

When they considered the continents move instead of the pole moving, the pathways correspond, ie Fitting the continents back together results in a single path............but the last sentence in the quote confuses me. It says that scientists consider that the continents are moving instead of the magnetic pole (ie consider the change in position and orientation of the continents), and this gives a perfect match of the apparent polar wander paths for different continents (North America and Europe, for example), but as they consider that the magnetic pole is not moving, why are there still pathways of polar wander? Is this the real MAGNETIC polar wander--the movement of the magnetic pole with respect to the geographic pole, which is considered stationary at most times?)

Edit: Ha...I have found a nice figure that claries what I mean...the following is the kind of thing I am saying, the paths of the bottom figure, are they the true magnetic polar wander throughout the earth's history?

kingwinner · 09-17-2005

What type of polar wandering is the single pathway in figure B of my picture?
If is the real magnetic polar wander throughout these 500 million of years, it looks strange to me as the path is moving very slow (it is a 500 million years path) comparing to today's magnetic pole moving rate. And also, for a long time the position of the magnetic pole should be averaged near the geogrpahic pole...the path in figure B just looks really strange to me because it's path does not average near the geogrpahic pole.....can someone please explain? I am puzzled...

Turtle · 09-18-2005

Quote:

Originally Posted by kingwinner

What type of polar wandering is the single pathway in figure B of my picture?
If is the real magnetic polar wander throughout these 500 million of years, it looks strange to me as the path is moving very slow (it is a 500 million years path) comparing to today's magnetic pole moving rate. And also, for a long time the position of the magnetic pole should be averaged near the geogrpahic pole...the path in figure B just looks really strange to me because it's path does not average near the geogrpahic pole.....can someone please explain? I am puzzled...

___It isn't clear to me how your sources use these terms. The Earth's magnetic poles do move around in relation to the geographic poles & even change their polarity (exchange North for South). I have to look for some timescales, but these movements have come to light through rock cores principally from undersea. As succesive flows of lava emerge from the spreading centers & cool, the iron elements lock into the alignment set by Earth's magnetic field. Presumably the scientists correct for plate drift as your attachted diagram implies.
___I saw a study recently wich used ship's compass records from as far back as the 18th century to plot the recent changing position of the Magnetic North Pole. Give a holler if this needs further clarification.

kingwinner · 09-19-2005

Some information about Apparent Polar Wander:
"Because the continents were moving ,there was an apparent polar wandering. Rocks in North America will have a magnetic alignment that points towards where the North Magnetic Pole was at that time. The continent then moves, so when we check its magnetic alignment today we find it pointing in an unexpected direction. And when the apparent polar wander paths of North America and Europe are compared, they are found to be different..."

But why in figure B, the 2 pathways are matched?

Turtle · 09-19-2005

Quote:

Originally Posted by kingwinner

But why in figure B, the 2 pathways are matched?

___It looks like they mean to show the "apparent" differences in the paths match when you put the continents back together.
___Funny though, when I visualize rotating the continents back together as illustrated in the diagram, I see the 2 paths diverging, not coinciding.