Living Time Capsules From a 3-Billion-Year-Old Earth
Living stromatolites growing in water saltier than the Dead Sea - modern analogs for 3-billion-year-old fossils, just meters from a highway. Here you can see what dominated Earth for its first 2 billion years.
Early Earth
In the shallow, ephemeral lakes adjacent to the main Coorong lagoon, a collection of dome-shaped leathery structures forms in the hypersaline water. These are living microbialites, specifically stromatolites, created by vast communities of microorganisms. They are modern examples of one of the most ancient life forms known, with fossilized stromatolites providing some of the earliest evidence of life on Earth, dating back over 3.5 billion years. For two billion years, these microbial structures were the dominant form of life on the planet.
The water chemistry in these satellite lakes is extreme. Salinity in the South Lagoon of the Coorong can exceed four times that of seawater, creating an environment where few other organisms can survive. This hypersalinity, caused by low freshwater input and high evaporation, allows the slow-growing microbial communities to thrive without competition from grazing animals. The water is also alkaline, with pH levels fluctuating between 8.2 and 9.9, and full of carbonate minerals like hydromagnesite and aragonite, which the microbes precipitate to build their stony homes.
These structures are formed by cyanobacteria and other microbes that trap and bind sedimentary grains, creating layered mats. Photosynthetic cyanobacteria, such as Microcoleus chthonoplastes, cement sand, cementing sand and other particles into distinctive layers. This process of building mineralized mats, layer by layer, results in the stromatolite structures. A single meter-high structure can take thousands of years to form.
A laboratory for planetary science
The Coorong stromatolites are a significant site for microbialite research. Because they are living, they are a analog to the ancient fossilized stromatolites that are so difficult to interpret. By studying the Coorong's microbial communities and the specific environmental conditions that allow them to form these structures, researchers learn about the ecosystems of the Precambrian world.
The various lakes in the Coorong system, such as North Stromatolite Lake and Halite Lake, display different mineralogies, from dolomite-magnesite to gypsum-aragonite, depending on their connection to marine or continental groundwater sources. This provides a natural laboratory for understanding how different water chemistries affect microbialite formation. The organisms here are part of a complex food web, with studies identifying a predominance of Proteobacteria, Cyanobacteria, and Bacteroidetes within the mats.
These modern examples help scientists understand the biological and environmental factors that controlled the shape and growth of ancient stromatolites. This knowledge is for understanding Earth's past. The conditions that support these life forms—highly saline mineral-rich water—may resemble environments that existed on other planets, like Mars. Studying the Coorong microbialites helps astrobiologists refine their search for signs of extraterrestrial life.
💡Fun Facts
The term stromatolite is Greek for 'layered rock'.
The South Lagoon of the Coorong can reach salinities of over 100 grams per liter, while the Dead Sea's salinity is around 34%.
Photosynthesizing stromatolites were responsible for the Great Oxygenation Event, which dramatically increased the oxygen in Earth's atmosphere about 2.4 billion years ago.
The oldest stromatolite fossils, found in Western Australia, are approximately 3.5 billion years old.
Coorong National Park is open daily, though it may close on days of Catastrophic or Extreme Fire Danger.
Admission
Vehicle entry fees apply. Camping fees are separate. Bookings should be made online.
Accessibility
Access to specific stromatolite sites may require 4WD vehicles or walking over sand dunes and salt flats. Some campgrounds are accessible by conventional vehicles.