RESEARCH.
Current research: Fossilisation processes (taphonomy). This is an exciting interdisciplinary field that integrates palaeontological, geological, and geochemical analysis to reconstruct the past depositional conditions (environment) and mechanisms of preservation in fossil deposits. Investigations rely on multidisciplinary approaches, including geological mapping, trace/rare earth element geochemistry, mineralogy, and palaeobiology (the biology of past life). It also relies upon investigations of active modern environments to understand past processes (the present is the key to the past!—Charles Lyell/James Hutton).
Taphonomy: The study of fossilisation processes — “how organisms die, decay, become buried, and fossilise/preserve in the fossil record. Or study of the grave!
Taphos [Greek] — grave or tomb.
Characterising past life on Earth offers significant insights into evolutionary and planetary processes. Discovering new fossil sites and understanding their formation furthers our knowledge of the relationships between our planet and its biosphere. This understanding not only sheds light on Earth’s past but also guides our predictions and preparations for its future.
GRADUATE RESEARCH.
The video below takes you on a journey to one of my favourite places on Earth, the rugged red landscape of the Pilbara region in Western Australia. The term ‘Pilbara’ derives from ‘bilybara’, meaning “dry country” in some languages of traditional custodians of the region, including the Nyamal and Banyjima. Pilbara rocks whisper tales of some of Earths oldest forms of fossilised life, stromatolites. These wrinkly old rocks were built by communities of simple, single-celled microorganisms. They help us understand the potential origins and evolution of life on Earth, and guide us in the search for life on Mars. I was lucky enough to have studied these Pilbara fossils for almost a decade – below is that story and the science born from it.
Doctor of Philosophy (PhD) | 2020
Geology
School of Biological, Earth & Environmental Sciences
The University of New South Wales
Supervisors: Prof. Martin Van Kranendonk | Prof. Carol Oliver
Thesis title | Scientific: Lithofacies and Biofacies analysis of Earth’s oldest subaerial hot spring deposits from the ca. 3.5 Ga Dresser Formation, Pilbara Craton, Western Australia
Thesis title | Plain English: Investigating all the rock types and all the fossil types (i.e., different layered rock structures built by microbes) that existed in 3.5-billion-year-old active hot water springs at an ancient volcano, which is now a desert we call the Pilbara of Western Australia.
Djokic, T., 2020 | PhD Thesis | Download
Abstract | Scientific
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 thesis provides detailed analysis of 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 are presented that 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 (Ml) 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.
Master of Philosophy (PhD) | 2015
Geology
School of Biological, Earth & Environmental Sciences
The University of New South Wales
Supervisors: Prof. Martin Van Kranendonk | Emeritus Prof. Malcolm Walter
Thesis title | Scientific: Assessing the link between Earth’s oldest convincing stromatolites and hydrothermal fluids: The c. 3.5 Ga Dresser Formation, North Pole Dome, Pilbara Craton, Western Australia
Thesis title | Plain English: Was there a link (or not) between some of Earth’s oldest known life (microbial) and hot water spring systems that existed 3.5-billion-years-ago?: Evidence from rocks and fossils in the Pilbara, Western Australia
Djokic, T., 2015 | MPhil Thesis | Download
Abstract | Scientific
Extensive mapping, petrological data and geochemical analyses shed new light on the environment of deposition of cherty sedimentary rocks that contain Earth’s oldest stromatolites in the c. 3.5 Ga Dresser Formation, North Pole Dome, Western Australia. Rapid lateral facies variations and diverse depositional settings, as well as multiple newly discovered eruptive layers of felsic volcaniclastic material, support a volcanic caldera setting. Importantly, the first discoveries of geyserite and tourmaline-bearing ferruginous laminates interpreted as radiogenic, B-rich hot spring crusts are documented, providing the first direct evidence of the emergence of inhabited volcanic land surface.
Abstract | Plain English
I walked a lot, across wrinkly old *rocks that stretch about 14 km. For one month. Documenting the rock layers and patterns. Sketching the rocks. Photographing the rocks. Collecting some rocks too. We sliced the rocks into thin slabs, glued them to glass slides and ground them extremely thin (0.03 mm). Looked at the rocks under a microscope. Identified their minerals and microscopic textures (Petrography). Looked at the rocks under a much more powerful microscope and identified the elements contained inside (geochemistry). All of this allowed us to identify the rock types (e.g., sandstone, mudstone etc) and put the geological puzzle together. We think that ancient life (represented by stromatolites = rock structures formed by bacteria) once lived in bubbling hot water springs in a volcanic landscape (like Yellowstone National Park, USA) 3.5 billion years ago!!! This work has extended our record of life living on land back by 3 billion years(!!). Could life have originated on land rather than in the ocean?
*Geological address —
Street: 3.5 billion year old Dresser Formation
Suburb: North Pole Dome
Town: Pilbara Craton
State: Western Australia
Tara Djokic (c) 2024
In the spirit of reconciliation, I acknowledge the Traditional Custodians of Country throughout Australia and their connections to land, sea and community. I pay respects to their Elders past and present and extend that respect to all Aboriginal and Torres Strait Islander peoples today.