Discredited hypotheses for the Cambrian explosion
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As our understanding of the events of the Cambrian becomes clearer, data has accumulated to make some postulated causes for the Cambrian explosion look improbable. Some examples are the evolution of herbivory, vast changes in plate tectonic rates or orbital motion, or different evolutionary mechanisms in force.
The appearance of herbivorous organisms
Stanley (1973) suggested that the appearance about 700 million years ago of protists (single-celled eukaryotes) that "cropped" microbial mats greatly expanded food chains and thus allowed rapid diversification, which led to the Cambrian explosion.[1] But it is now thought that "cropping" arose before 1 billion years ago, as stromatolites began to decline about 1.25 billion years ago.[2]
Changes in orbital parameters
References
- ^ Stanley, S.M. (May 1973). "An Ecological Theory for the Sudden Origin of Multicellular Life in the Late Precambrian". Proc Natl Acad Sci U S A. 70 (5): 1486–1489. doi:10.1073/pnas.70.5.1486.
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