The break-up of Rodinia, birth of Gondwana, true polar wander and the snowball Earth

A major global plate reorganisation occurred between similar to 750 and sim ilar to 550 Ma. Gondwana was assembled following the dispersal of Rodinia, a supercontinent centred on Laurentia in existence since similar to 1050 Ma . The reorganisation began when tectonic elements, later composing East Gon dwana, rotated piecemeal away from the Pacific margin of Laurentia. These e lements swept across the ancestral Pacific (Mozambique) Ocean that lay betw een Laurentia and the combined African cratons of Congo and Kalahari, which were loosely joined after similar to 820 Ma. Simultaneously, the Adamastor (Brasilide) Ocean closed by subduction bordering the West Gondwana cratons , drawing virtually all of Gondwana together by similar to 550 Ma. The fina l assembly of Gondwana occurred contemporaneously with the separation of La urentia from West Gondwana. It has been postulated that the imprint of Rodinia's long-lived existence o n lower mantle convection produced a prolate ellipsoidal geoid figure. This could give rise to episodic inertial-interchange true polar wander (IITPW) , meaning that the entire silicate shell of the Earth (above the core-mantl e boundary) rolled through 90 degrees with respect to the diurnal spin axis in similar to 15 Ma (equivalent to an apparent polar wander velocity of si milar to 66 cm a(-1)). Although empirical arguments for IITPW of Cambrian a ge appear to be flawed, evidence for an ultra-fast ( > 40 cm a(-1)) meridio nal component of apparent polar wander for Laurentia between 564 and 550 Ma suggests that IITPW might have occurred at that time. The break-up of Rodinia increased the continental margin area and preferent ial organic C burial globally, which is reflected by high delta(13)C values in seawater proxies. The consequent drawdown of CO2 is implicated in a suc cession of runaway ice-albedo catastrophes between similar to 750 and simil ar to 570 Ma, during each of which the oceans completely froze over. Each " snowball" Earth event must have lasted for millions of years because their terminations depended on extreme CO2 levels, built up by subaerial volcanic outgassing in the absence of sinks for C. A succession of ice-albedo catas trophes, each terminated under ultra-greenhouse conditions, must have impos ed an intense environmental filter on the evolution of life. They may have triggered the radiation of Ediacaran fauna in the aftermath of the final sn owball event. It is increasingly recognised that the Late Neoproterozoic wa s one of the most remarkable periods in Earth history, and it appears to ex emplify the interplay of tectonics, the environment and biology in deep tim e. (C) 1999 Elsevier Science Limited. All rights reserved.