The rise of multicellular animals about 540 million years ago was a turning point in the history of life. A group of Finnish scientists suggests a new climate-biosphere interaction mechanism for the underlying processes.
Photo: Antti Samuli
The theory invokes cold, ice-containing climates as a key precursor for
multicellular life. If the model turns out to be correct, one can assume that complex life might exist also around stars which are more massive and short-lived than the Sun. Since remote sensing of highly reflecting glaciers should be possible, this may help designing future astronomical observation programmes for earthlike extrasolar planets.
Multicellular life was preceded by the cold Neoproterozoic climate 600-800 million years ago which at times produced widespread glaciations. According to the new theory, the coldness was due to low carbon dioxide concentration brought about by strong algal growth in the oceans. The algal growth was maintained by the lack of grazing animals and the ability of cold seawater to mix and transport nutrients efficiently. A moderately high seawater oxygen concentration developed as a byproduct of the algal growth. This enabled diffusive breathing of primitive multicellulars which were larger than their
unicellular counterparts. The ability of cold water to contain more dissolved oxygen also helped the multicellulars to thrive.
The diversification of the marine food webs introduced by multicellular
predators as well as the moving and burrowing activity of animals on the seafloor contributed to a more efficient decomposition of the algae-produced organic carbon, which slowed the rate of organic carbon sequestration. This in turn increased the atmospheric carbon dioxide level and ended the severe glaciations and the reign of unicellular algae, initiating the development of a modern-type climate.
Pekka Janhunen, Finnish Meteorological Institute, firstname.lastname@example.org
Hermanni Kaartokallio, Finnish Institute of Marine Research,
Ilona Oksanen, University of Helsinki, email@example.com
Kirsi Lehto, University of Turku, firstname.lastname@example.org
Harry Lehto, University of Turku, email@example.com