The Cambrian explosion: Plume-driven birth of the second ecosystem on Earth

Abstract

The birth of modern life on Earth can be linked to the adequate supply of nutrients into the oceans. In this paper, we evaluate the relative supply of nutrients into the ocean. These nutrients entered the ocean through myriad passageways, but primarily through accelerated erosion due to uplift. In the 'second ecosystem', uplift is associated with plume-generation during the breakup of the Rodinia supercontinent. Although the evidence is somewhat cryptic, it appears that the second ecosystem included the demospongia back into the Cryogenian (~. 750. Ma). During the Ediacaran-Cambrian interval, convergent margin magmatism, arc volcanism and the closure of ocean basins provided a second pulse of nutrient delivery into the marine environment. A major radiation of life forms begins around 580. Ma and is represented by the diverse and somewhat enigmatic Ediacaran fauna followed by the Cambrian Explosion of modern phyla during the 540-520. Ma interval. Tectonically, the Ediacaran-Cambrian time interval is dominated by the formation of ultra-high pressure (UHP), high pressure (HP) and ultra-high temperature (UHT) orogenic belts during Gondwana orogenesis. Erosion of this extensive mountainous region delivered vast nutrients into the ocean and enhanced the explosiveness of the Cambrian radiation. The timing of final collisional orogeny and construction of the mountain belts in many of the Gondwana-forming orogens, particularly some of those in the central and eastern belts, post-date the first appearance of modern life forms. We therefore postulate that a more effective nutrient supply for the Cambrian radiation was facilitated by plume-driven uplift of TTG crust, subsequent rifting, and subduction-related nutrient systems prior to the assembly of Gondwana. In the outlined scenario, we propose that the birth of the 'second ecosystem' on our planet is plume-driven. © 2013 International Association for Gondwana Research.