Astrobiology from early signs of life
Implications for astrobiology from early signs of life preserved in the Pilbara, Western Australia
Speaker: Dr Tara Djokic
The study of early life on Earth provides insights into the potential environments where life may have arisen, informs on life’s earliest metabolisms and habitats, and can guide the search for life in the solar system and beyond. This presentation describes lithofacies and biofacies associated with Earth’s oldest subaerial hot spring deposits from the lower chert-barite sequence of the ca. 3.5 Ga Dresser Formation (DFc1), Pilbara Craton, Western Australia. Stratigraphic, petrographic, morphologic, and geochemical data document a range of microbially inhabited hot spring deposits, which formed on an emerged land surface within a hydrothermally-active, low-eruptive volcanic caldera complex. Detailed mapping and stratigraphic analysis along the entire eastern exposure (~14 km) of DFc1 in the North Pole Dome has defined four members (M1-M4). Lithostratigraphic data is linked with rare earth element and yttrium data (REE+Y) that, together, show a transition upsection from marine (M1) to terrestrial (M2) conditions, and back to marine conditions (M3-M4). These transitions are interpreted to reflect magmatic inflation causing crustal uplift during M1 and M2, followed by deflation causing caldera collapse during M3 and M4. A caldera model is supported by rapid lateral facies changes at a local scale, controlled by active growth faults now occupied by hydrothermal chert+barite veins. Hot spring sinter (geyserite) and possible travertine (terracette+shrub) deposits are associated with a range of microbial biosignatures including stromatolites, shrub-like microbialites, microbial palisade fabric, and bubbles trapped in the mineralised remnants of inferred microbial exopolymeric substance (EPS). Concentrations of boron in deposits associated with hot spring sinters may indicate another composition of hot spring fluids. Dresser hot spring, and related lithofacies and biofacies are texturally and chemically comparable to proximal, middle and distal hot spring facies characteristic of Phanerozoic subaerial geothermal deposits e.g., Yellowstone National Park, USA, New Zealand and the Drummond Basin of Queensland, Australia. The results of this study have significant implications for the origin of life on Earth by expanding our geological perspective on the available environments inhabited by very early life, and may play an important role in the search for life in temporally relevant hot spring systems on Mars.
Dr Tara Djokic recently completed her PhD at the University of New South Wales (UNSW) in Sydney, Australia. Her PhD work was focussed on some of the earliest evidence for life on Earth and its implications for the field of astrobiology. She is also very interested in science communication and science education having produced a geological virtual field trip (VFT) that has, since 2016, been used to teach geological aspects of astrobiology at UNSW. She is currently a researcher in the Palaeontology department at the Australian Museum in Sydney.
AGM of the Hunter Valley Branch, GSA will start after the talk at 6pm
BYO drinks and nibbles from 5.15 pm
Presentation starts at 5.30 pm
AGM after talk at 6 pm