image: Silica-gel based chromatographic columns show the separation of 1.1 billion-year-old bitumen from Mauritania and highlight the pink color of the geoporphyrins. view more
Credit: PNAS
A study suggests that around 1 billion years ago, photosynthetic primary producers were likely too small to support the development of animal ecosystems. Approximately between 1.8 and 0.8 billion years ago, in the mid-Proterozoic Eon, Earth's oceans contained virtually no animal life. A complex ecosystem requires sufficiently large primary producers, such as phytoplankton and algae, to provide the flow of trophic energy that would support animal life. Researchers have hypothesized that the mid-Proterozoic ocean may have lacked such large producers. Jochen J. Brocks and colleagues examined porphyrins, fossil chemical signatures of the pigment chlorophyll, from 1.1 billion-year-old shales in Mauritania. Analysis of nitrogen isotopes in the porphyrins revealed signatures suggesting that cyanobacteria may have been the dominant form of primary producers. Further evidence from fossil carotenoid pigments suggest that green and purple sulfur bacteria may have also served as primary photosynthetic producers. Although the shales contained eukaryotic microfossils, failure to detect sterane fossil molecules that would indicate eukaryotic contribution to biomass suggests that algae may have played a minimal or insignificant role in the oceans around 1 billion years ago. According to the authors, lack of large primary producers in the mid-Proterozoic oceans, along with low oxygen levels, may have hampered the development of animal life.
Article #18-03866: "1.1-billion-year-old porphyrins establish a marine ecosystem dominated by bacterial primary producers," by Nur Gueneli et al.
MEDIA CONTACT: Jochen J. Brocks, Australian National University, Canberra, AUSTRALIA; tel: +61432470006; e-mail: <jochen.brocks@anu.edu.au>
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