China
Africa
Explore chapters and articles related to this topic
Geomagnetic Field Effects on Living Systems
Published in Shoogo Ueno, Tsukasa Shigemitsu, Bioelectromagnetism, 2022
It is conceivable that the cause of the Cambrian explosion could be related to the termination of the “snowball Earth,” which is global glaciation that the whole Earth was frozen during the most severe ice age of Precambrian time. Here, the term “snowball Earth” was coined by a geobiologist, Joseph Kirschvink of the California Institute of Technology (Caltech), in a short paper published in 1992 within a lengthy volume concerning the biology of the Proterozoic Eon (Kirschvink, 1992). The major contributions from his insight were: (1) the recognition that the presence of banded iron formations is consistent with such a global glacial episode, and (2) the introduction of a mechanism by which to escape from a completely ice-covered Earth, specifically, the accumulation of CO2 from volcanic outgassing leading to an ultra-greenhouse effect (Kirschvink, 1992). Moreover, Hoffman et al. (1998) suggested that the snowball Earth ended abruptly when subaerial volcanic outgassing raised atmospheric CO2 to about 350 times the modern level. The rapid termination would have resulted in a warming of the snowball Earth to extreme greenhouse conditions (Hoffman et al., 1998). The CO2 transfer to the ocean would result in the rapid precipitation of calcium carbonate in warm surface waters, producing the cap carbonate rocks observed globally (Hoffman et al., 1998). However, it was supposed that it would be an indirect relationship, if any, because the Cambrian explosion started at least 32 Myr after the end of the snowball Earth (Marshall, 2006). Moreover, the cold periods of the snowball Earth may even have delayed the evolution of large size organisms (Bengtson, 2002).
Geological setting of exceptional geological features of the Flinders Ranges
Published in Australian Journal of Earth Sciences, 2020
Neoproterozoic glaciogenic deposits are widely distributed on all continents except Antarctica but their distribution and mode of occurrence contrast with Phanerozoic analogues (Hoffman & Schrag, 2002). They provide evidence of the most widespread and long-ranging glaciations on Earth. Distinctive ‘cap’ carbonate layers sharply overlie most Neoproterozoic glaciogenic successions without significant hiatus, implying a sudden switch back to a warmer climate. However, in the Adelaide Geosyncline, a significant break, in places with erosion and even tectonic tilting, separates the Sturtian cap carbonate from the underlying glaciogenic sediments. Cap carbonates have unusual sedimentological, geochemical and isotopic characteristics not found in other Neoproterozoic or Phanerozoic carbonates and they occur even in successions otherwise lacking carbonate (Hoffman & Schrag, 2002). At least two major worldwide glacial periods are evident, interspersed with periods of relatively warm climate, with glaciers interpreted to reach sea-level at low paleolatitudes.