A case for an active eukaryotic marine biosphere during the Proterozoic era

Lisa K. Eckford-Soper*, Ken H. Andersen, Trine Frisbæk Hansen, Donald E. Canfield

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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Abstract

The microfossil record demonstrates the presence of eukaryotic organisms in the marine ecosystem by about 1,700 million years ago (Ma). Despite this, steranes, a biomarker indicator of eukaryotic organisms, do not appear in the rock record until about 780 Ma in what is known as the "rise of algae." Before this, it is argued that eukaryotes were minor ecosystem members, with prokaryotes dominating both primary production and ecosystem dynamics. In this view, the rise of algae was possibly sparked by increased nutrient availability supplying the higher nutrient requirements of eukaryotic algae. Here, we challenge this view. We use a size-based ecosystem model to show that the size distribution of preserved eukaryotic microfossils from 1,700 Ma and onward required an active eukaryote ecosystem complete with phototrophy, osmotrophy, phagotrophy, and mixotrophy. Model results suggest that eukaryotes accounted for one-half or more of the living biomass, with eukaryotic algae contributing to about one-half of total marine primary production. These ecosystems lived with deep-water phosphate levels of at least 10% of modern levels. The general lack of steranes in the pre-780-Ma rock record could be a result of poor preservation.
Original languageEnglish
Article numbere2122042119
JournalProceedings of the National Academy of Sciences of the United States of America
Volume119
Issue number41
Number of pages12
ISSN0027-8424
DOIs
Publication statusPublished - 2022

Keywords

  • Eukaryote
  • Evolution
  • Proterozoic
  • Marine
  • Ecosystem modeling

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