Donald Canfield: The evolution of Eukaryote ecosystems

Professor in biology at University of Southern Denmark and director of the Nordic Centre for Earth Evolution.

Donald CanfieldHis research include studies of geological-biological interactions, including development of the oxygen abundance in Earth’s atmosphere through geological times and during Earth’s great oxidation event, the relation between oceanic sulfur concentration, carbon cycles and animal evolution.

Further information: Donald Canfield on Wikipedia

Abstract: The fossil record suggests that eukaryotes were part of the marine ecosystem by about 1700 million years ago. However, the accepted biomarker record of steranes, derived from eukaryotic sterols, do not appear in the rock record until about 780 Ma in what is known the “Rise of Algae”. To explain this time gap, it is variably argued that either eukaryotes were minor shadow members of marine ecosystems for almost 1 billion years after they first appeared, or that the early fossils represent “stem group” organisms that first evolved into “crown group” eukaryotes capable of “modern”-style sterol production around 800 million ago. In this view, complex eukaryote ecosystems with both photosynthesis and grazing also emerged with this relatively late evolution of crown group organisms. We challenge these views. First, using high temperature pyrolysis techniques, we find “modern” steranes in rocks from 1400 and 1000 million years ago, demonstrating that crown-group Eukaryotes evolved before 1400 million years ago. Next, we use a size-based ecosystem model to show that the size distribution of preserved eukaryotic microfossils from 1700 Ma and onwards required an active and complex eukaryote ecosystem complete with photosynthesis and grazing. This result is robust over a wide range of nutrient concentrations. Furthermore, our model results suggest that these ancient eukaryote ecosystems could have provided from one third to one half of the marine primary production. Thus, complex eukaryote ecosystems were likely active from 1700 million years ago and onwards. In this view, the general lack of steranes in the pre-780 Ma rock record could be a result of poor preservation.