HR: 0800h
AN: ED51A-0007    [Abstracts]
TI: Rodinia, She Do Spin: A (prequal) tribute to the legendary 2001 AGU poster, "Pangaea, She No Spin"
AU: * Stegman, D
EM: dave.stegman@sci.monash.edu.au
AF: Monash Cluster Computing, Schoold of Mathematical Sciences, Monash University, Clayton, VIC 3800 Australia
AU: Knight, K
EM: kbk@uclink.berkeley.edu
AF: Department of Earth and Planetary Science, University of California, Berkeley, McCone Hall, University of California, Berkeley, Berkeley, Ca 94720 United States
AB: On one side of the poster: actual science, real equations, a burning question many scientists are researching by employing the best resources governments can provide; on the other side of the poster: a shameless and ill-fated attempt to conceptualize the problem using rudimentary and commonly available crafts. Unbenownst to passers-by, meticulous, covert record keepers will busily tabulate which of the two presentation styles draws more attention and for what length. Late night television the world over asks such simple questions: Will it float? (David Letterman); What was weak? (Australian Broadcasting Corporation's "Double the Fist" show); etc. Borrowing a page from popular culture we adopt a simple and interesting question: Does it spin? This question has been posed previously in rigorously mathematical terms in relation to true polar wander (TPW) (Ricard et al, 1993), in descriptive terms in relation to paleomagnetic data sets (Evans, 2003), and also in more interesting terms (McDowell, 2001). This poster draws on the success of the latter presentation which described the 2001 experiment thusly, "I wondered what would happen if the configuration were put in high relief on a globe and spun on axis. Then I wondered if the present configuration of land masses would itself balance as a spinning top. So I got two Replogle globes, two boxes of colored modeling clay sticks, and two fat knitting needles, to fit through the capped holes at the poles of the globes. The clay sticks I cut up into 3 mm. (1/8") slices, using a different color for each continent, and applied to the first globe, assuming the extreme exaggeration above the geoid, no matter how crude, would tell the story. Inserting one needle through the globe and securing it, I balanced the globe on the point of the needle and twirled it like a top. Result: Wobbly! Top end of needle gyrated unevenly, and here it was supposed to make a smooth precessional cone. Oh boy. For the second globe, I used a Scotese "free stuff" interpretation of Pangaea, which I had to augment considerably using USGS, DuToit, Irving and other references, fitting it on the globe and applying identical clay color slices to what I judged generally accepted land surfaces. Result: the thing would hardly stand up, let alone spin." We will indeed present new results relavent to the issue of whether Earth experienced an increased amount of rotational instability (i.e. TPW) duing the Proterozoic as a result of the Rodinia supercontinent. We make the assumption that the viscosity structure of the mantle has not changed significantly since the Neoproterozoic, and that the configuration of tectonic plates into a supercontinent (testing multiple plausible reconstructions) and the internal density anomalies resulting from such tectonic patterns will drive changes in the time varying moment of inertia tensor. So basically, we got a really big computer, a really fast mantle convection program written in F77, a few different plate reconstructions, generated a mantle density structure and then calculated the response for changes in the spin axis. We also create an "analog" model using crafts, including but not limited to, elbow macaroni, glitter, popsicle sticks, and felt. Without resorting to conclusion that the Earth must have been a smaller size in the past, we will present our findings because Rodinia, she do spin.
DE: 8159 Rheology--crust and lithosphere
DE: 5450 Orbital and rotational dynamics
DE: 1239 Rotational variations
DE: 1525 Paleomagnetism applied to tectonics (regional, global)
SC: Education and Human Resourcese [ED]
MN: 2004 AGU Fall Meeting