Another Cambrian Explosion Theory

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

Authors:

1. M. Santosh (a, b)
2. S. Maruyama (c)
3. Yusuke Sawaki (d)
4. Joseph G. Meert (e)

Affiliations:

a. School of Earth Sciences and Resources, China University of Geosciences, 29 Xueyuan Road, Beijing 100083, China

b. Division of Interdisciplinary Science, Faculty of Science, Kochi University, Kochi 780-8520, Japan

c. Earth Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8551, Japan

d. Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan

e. Department of Geological Sciences, 241 Williamson Hall, University of Florida, Gainesville, FL 32611, USA

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.