Western Australia is considered one of the most important research areas on the origin and evolution of early life on Earth. Key evidence in these studies is the significant microbialite sites distributed throughout the State. ‘Living’ fossil sites can be found in Western Australin rocks that are over 539 million years old.
What are microbialites?
‘Microbialite’ is the name given to structures built by a community of microbes. These microbes regularly build flat carpet-like structures, called microbial mats. The word ‘microbialite’ is usually reserved for features that rise above the sediment surface, in the form of mounds or groups of mounds.
Microbialites are categorised based on their internal structure, those with:
- internal laminae or layering known as stromatolites (like some in Shark Bay)
- structures with a clotted or ‘cauliflower’ fabric called thrombolites (like at Lake Clifton)
Many of these microbes and the structures they build were very common during the Proterozoic Eon (2.5 billion to 538.8 million years ago). Living microbialites are mostly found in environments that other organisms cannot tolerate like salt lakes, sea bays with restricted water circulation, and hot springs.
Examples of living microbialites can be seen at:
- Hamelin Pool in Shark Bay
- Lake Clifton near Mandurah
- Lake Thetis near Cervantes
- Lake Richmond, near Rockingham
Microbialites in Western Australia
For the past 40 years, the Geological Survey of Western Australia (GSWA) has been documenting sites in the eastern Pilbara that contain some of the world’s oldest fossils and studying microbialites in many of Western Australia’s Proterozoic basins.
We have organised excursions to these areas so that visiting geologists, palaeobiologists and astrobiologists can examine these important fossils in their geological context. The sites have also featured in popular science and the media.
Highlights of microbialites found in our State include:
- Some of the world’s oldest known fossil examples (3.45 billion years old), found near Marble Bar in the Pilbara.
- one of the most continuous and best-studied records of fossil microbialites, with examples from a broad range of geological periods.
- some of the best examples of living microbialites at Hamelin Pool and various lakes — these are ‘living laboratories’ where the structures, the environments in which they form, and the processes that form them, can be studied. The results can be applied to the interpretation of comparable structures in the geological record.
How microbialites form
Microbialites are built by a community of microbes, with modern examples commonly including photosynthetic cyanobacteria as the dominant component.
Characteristics of microbialite formation include the following:
- within the mat, microbes will either trap and bind sediments or precipitate minerals forming alternating layers of organic-rich filaments and sediments.
- microbes will then slowly move up through deposited layers to reach light or an energy source, thereby progressively forming new layers on the outer surface. Trapped or precipitated sediments in the older layers within the structure will then harden into rock (lithify).
- over long periods of time, these layers of sediments and microbes build up to form stratiform, domical, columnar, conical, or complex branching structures.
- many microbes are photosynthetic and produce oxygen because of their metabolic activities. In the Proterozoic, such organisms converted Earth's atmosphere from one dominated by greenhouse gases to one with breathable oxygen.
The importance of studying microbialites
Like other fossil groups in younger rocks, we use microbialites for biostratigraphic correlation in Proterozoic basins. The presence of the same types of microbialites in geographically different areas can indicate that the rocks formed during the same period of geological time.
Microbialites are used to better interpret the method or environment of formation for the rocks they are found within. Western Australia has become a world leader in the geological interpretation of these fossils.
Astrobiologists are interested in microbialites because of the search for life on Mars. Earth and Mars probably shared similar early histories. Exploration of the surface of Mars has uncovered considerable evidence that Mars once had environments suitable for microbialite growth. The Pilbara provides many significant examples of early life fossils that have been used to inform the exploration for Martian fossils.
Mineral and petroleum explorers are also interested in understanding where and how microbialites and other early fossils form, as the basins they form in are often endowed with precious resources.
There are worldwide examples of mineral deposits forming in and around microbialites. Mineral-rich waters can flow through the spaces within the structures and deposit ore minerals. The spaces in the microbialites can also trap and store hydrocarbons like gas and oil. The organisms that form microbialites are a known source of petroleum, making them interesting targets for petroleum exploration.
Protecting Western Australia’s oldest fossils
The oldest known structures thought to have been formed by microbes are found within Buick Reserve, near the historic North Pole mining area. Slightly younger and more certainly stromatolitic examples are located further south within the Trendall Reserve, which was discovered in 1984 by former GSWA Director Dr Alec Trendall.
Trendall Reserve contains some of the most convincing evidence for the formation of these ancient microbialites by microbes, as opposed to features formed purely by inorganic (non-living) processes. These include large cone-shaped stromatolites that grow up to 1m high, smaller cone-shaped structures that look like egg cartons, and dome-shaped forms that branch into columns.
These sites and four others (Awramik, Lowe, Schopf, and Hickman) have been declared State Geoheritage Reserves to protect vital field evidence. Permission is needed to visit or carry out activities like sampling within these Reserves.
The ‘Dawn of Life Trail’ site is located 60km south of Marble Bar and 1km west of the Marble Bar on Nullagine Road. Here you can see fossils like those at the remote scientific sites. Visitors are asked to refrain from collecting and to treat the fossils at the site with respect, so that future generations may also enjoy them.
Many of the fossils discussed here, including the Trendall ‘egg carton’ stromatolites, can be seen in the WA Museum Boola Bardip’s Origins gallery.
Do your part to protect Western Australia’s fossils by staying up to date with the restrictions and responsibilities related to fossils and State geoheritage, following all laws and regulations, following all laws and regulations, and spreading the word to others (including tourists).
