STROMATOLITES: OUR SOLAR SYSTEM’S OLDEST FOSSILS

Stromatolites are layered colonial structures formed by cyanobacteria (also referred to as “blue-green bacteria.” They are found in warm, waters, mainly in marginal-marine environments, namely, the supratidal, intertidal, and, shallow subtidal zones. They form squishy, sticky mounds of communal-living microbs that need sunlight. In the process, these microbes produce free oxygen via photosynthesis, and they were extremely important in producing the free oxygen in Earth’s early atmosphere. Today, stromatolites are rare because they fell victim to crazing animals.

They are the oldest fossils known on Earth, where their geologic range is 3.5 billion years ago (Early Archean) to today. Fossil stromatolites about the same age (3.7 billion) have also been found recently in outcrops on the planet Mars, in the Meridiani Planum, by means of explorations associated with the NASA rovers "Opportunity", "Spirt", and "Curiosity" (Rhawn et al. 2020). 

1  Precambrian stromatolite, Asburn Formation, Saint John, New Brunswick, Canada. This rock is about 12 inches in length.

2 Precambrian? stromatolite, eastern California. The orange arrow points to a USA nickel (diameter 2.1 cm) used for scale.

3A-C: Three successive views (oblique top, and side) of the same  2.5-inch “cube” of rock, cut out (and subsequently polished) of a Precambrian stromatolite (locality unknown),

4 : Diagram showing stromatolite environments at Shark Bay, West Australia.

5: A vertical-cross section of a modern-day intertidal stromatolite from Shark Bay, West Australia showing a “cabbage-head”-like, porous internally layered structure. The base of this stromatolite encrusts a rock. Based on studies from this locale, stromatolites grow at a maximum of only 0.3 mm per year.

6: This image shows how the Shark Bay stromatolites and associated boardwalk were severely damaged by strong surge waves generated by the severe tropical cyclone Seoja in April, 2021. (The site is still currently closed to the public until ?). The four domal-shaped structures (located between the two pilings) are the tops of stromatolites (exposed at low tide). It will take thousands and thousands, etc. of years for the stromatolites to redbuild to their previous sizes. Image kindly provided by Matt Ventimiglia, 2023.  

7: Tidepool stromatolites, northern Gulf of Baja California, Mexico, 1974.

Reference Consulted:

Rhawn, J.G. et al. 2020. Oceans, lakes, and stromatolites on Mars. Advances in Astronomy. DOI:10:1155/2020/695932. Open access.