EARTH SYSTEM SCIENCE
WRITING ASSIGNMENT #7 - RECONSTRUCTING PLATE MOTIONS
Geologists have been able to reconstruct the motions of Earth's tectonic plates through history using the remnant magnetism of volcanic rocks extruded on the continents and (especially) along the mid-ocean ridges (divergent plate boundaries). The paper you read by Muller et al. provides a very brief (and somewhat technical) description of the method used to do this.
Beginning with speculative thoughts of Harry Hess in the1960's, marine geologists realized that the mid-ocean ridge system was the primary source of new crustal material and that these materials emanated sequentially from the ridge crests all over the world. This created a novel type of geology on the Earth's ocean floors - namely that rocks became progressively older with increasing distance from the ridges! In addition, by determining the age of samples of seafloor rocks and by measuring the remnant magnetism of the seafloor, geologists have been able to create detailed maps of the age-structure of the world's oceans. On this map, the "hot" (red) colors represent young rocks (note they are close to the ridge crests) while the "cold" (blue) colors are found at the margins of the ocean basins.
In order to reconstruct plate motions, all one needs to do is back-track across the ocean basin by progressively removing young rocks, then replotting the continental positions with respect to the poles of rotation of the individual plates (ok, that's not easy, but it can be done). This process is carried out repeatedly until the continents are joined into a single land mass - this event occurred about 260 million years ago. Speculation that the continents had once been joined was first represented on maps by Antonio Snider-Pellegrini. Later, the German Meteorologist, Alfred Wegener, named the supposed supercontinent Pangea. Of course, Snider-Pelligrini and Wegener had no idea how the process actually worked, but their speculations were moving them in the right direction.
YOUR ASSIGNMENT FOR THIS WEEK:
Your task this week is to create an animated visualization of continental drift and evolution of the Atlantic Ocean basin using your Windows Movie Maker software and images in the papers "Digital Isochrons of the World's Ocean Floor" by Muller et al. and "A Global Isochron Chart" by Royer et al. The method we will use is simple - just follow the instructions below:
Here's what to do:
1. Click on the button below to access the paper by Royer et al. at the Geological Survey of Canada server to find out how this was done.
2. Click on the "Color images of plate reconstruction with isochrons" link to see the raw images I used to create the images below.
3. Download each of the 17 images showing plate reconstructions through the last 180 million years from the collection below.
a. Click on the link for each image.
b. When the image is displayed, click the right mouse button and "Save Image As".
c. Save the image in .BMP format to your computer.
4. Start up Windows Movie Maker. Drag and drop each image in chronological order onto the film strip. Determine an appropriate timing for each image, and create a movie showing the break-up of Pangea.
5. Save the movie on your desktop as "PangeaMovie.wmv" so Mr. Sharif and I can review your work.
A Global Isochron Chart
RETURN TO EARTH SYSTEM SCIENCE HOME PAGE
