Evidence of eukaryotes during the Paleoproterozoic rise in atmospheric oxygen

Event type: 
21 November 2019

Pioneer Theatre, AGSM

Erica Barlow

From the fossil record, we know that life inhabiting the early Earth (>2.5 bya) consisted only of small, microscopic cells, which commonly grouped together in colonies and formed layered structures called stromatolites. We also know that at some point during the proceeding couple of billion years, life developed in both size and complexity, eventually forming macroscopic animals some 540 million years ago (aka the ‘Cambrian Explosion’). Yet, the exact timing of the transition from simple, prokaryotic life to more complex, eukaryotic life remains elusive, with the oldest unambiguous eukaryotic microfossil being from ~1.6 byo rocks.

It is recognised that environmental pressure can drive evolutionary change. Thus, it has been suggested that the significant increase in atmospheric oxygen at ~2.45-2.3 bya, known as the Great Oxidation Event (GOE), may have triggered the development of more complex, eukaryotic life. However, a lack of fossiliferous rocks of this age worldwide has meant that it has not, so far, been possible to test this idea.

During the course of my PhD, I described several different microfossils from a new deposit in Western Australia that dates from this ~2.4 byo time period. These microfossils inhabited both shallow- and deeper-water settings, giving insight into a marine ecosystem during the rise of atmospheric oxygen.

One microfossil type, in particular, displays tantalising similarities to modern eukaryotic coenobial algae, which suggests it could represent the oldest eukaryotic microfossil in the geological record. If so, this would push the record of eukaryotic microfossils back by as much as 800 million years, and provide support for the theory of eukaryotes arising in response to the GOE.

Erica is a PhD candidate within the Australian Centre for Astrobiology, PANGEA, and BEES. She submitted her thesis in September of this year.