title: Biological feedbacks as cause and demise of the Neoproterozoic icehouse: astrobiological prospects for faster evolution and importance of cold conditions.
abstract: Several severe glaciations occurred during the Neoproterozoic eon, and especially near its end in the Cryogenian period (630-850 Ma). While the glacial periods themselves were probably related to the continental positions being appropriate for glaciation, the general coldness of the Neoproterozoic and Cryogenian as a whole lacks specific explanation. The Cryogenian was immediately followed by the Ediacaran biota and Cambrian Metazoan, thus understanding the climate-biosphere interactions around the Cryogenian period is central to understanding the development of complex multicellular life in general. Here we present a feedback mechanism between growth of eukaryotic algal phytoplankton and climate which explains how the Earth system gradually entered the Cryogenian icehouse from the warm Mesoproterozoic greenhouse. The more abrupt termination of the Cryogenian is explained by the increase in gaseous carbon release caused by the more complex planktonic and benthic foodwebs and enhanced by a diversification of metazoan zooplankton and benthic animals. The increased ecosystem complexity caused a decrease in organic carbon burial rate, breaking the algal-climatic feedback loop of the earlier Neoproterozoic eon. Prior to the Neoproterozoic eon, eukaryotic evolution took place in a slow timescale regulated by interior cooling of the Earth and solar brightening. Evolution could have proceeded faster had these geophysical processes been faster. Thus, complex life could theoretically also be found around stars that are more massive than the Sun and have main sequence life shorter than 10 Ga. We also suggest that snow and glaciers are, in a statistical sense, important markers for conditions that may possibly promote the development of complex life on extrasolar planets.
authors.affiliation: Department of Physical Sciences, University of Helsinki, Helsinki, Finland. pekka.janhunen@fmi.fi
authors.forename: Pekka
authors.initials: P
authors.lastname: Janhunen
authors.forename: Hermanni
authors.initials: H
authors.lastname: Kaartokallio
authors.forename: Ilona
authors.initials: I
authors.lastname: Oksanen
authors.forename: Kirsi
authors.initials: K
authors.lastname: Lehto
authors.forename: Harry
authors.initials: H
authors.lastname: Lehto
mesh_terms: D044822:Biodiversity; D002245:Carbon Dioxide / Q000737:chemistry / Q000378:metabolism; D002247:Carbon Isotopes / Q000032:analysis*; D003081:Cold Climate; D018534:Earth, Planet; D056890:Eukaryota / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D019419:Evolution, Planetary; D018559:Exobiology; D025461:Feedback, Physiological; D017752:Greenhouse Effect; D046448:Ice Cover; D008386:Marine Biology; D000069497:Origin of Life; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D010788:Photosynthesis; D010839:Phytoplankton / Q000502:physiology*; D012623:Seawater / Q000737:chemistry; D016082:Solar System; D012995:Solubility
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D010100:Oxygen