What are Stromatolites?

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What are Stromatolites? Blog Image


Scientists recently unearthed living stromatolites—ancient geological structures made from algae—on Sheybarah Island, nestled on the northeastern shelf of the Red Sea in Saudi Arabia.

About Stromatolites:

  • Stromatolites, or stromatoliths, are layered accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary grains by biofilms of microorganisms, especially cyanobacteria (commonly known as blue-green algae).
    • As sediment layered in shallow water, bacteria grew over it, binding the sedimentary particles and building layer upon millimetre layer until the layers became mounds.
  • These structures are usually characterized by thin, alternating light and dark layers that may be flat, hummocky, or dome-shaped. 
  • Stromatolites were common in Precambrian time (i.e., more than 542 million years ago).
  • Most stromatolites are marine, but some forms from Proterozoic strata more than 2 ½ billion years old are interpreted as inhabiting intertidal areas and freshwater ponds and lakes.
  • Living stromatolites are found in only a few salty lagoons or bays on Earth.
  • Western Australia is internationally significant for its variety of stromatolite sites, both living and fossilised.
    • Shark Bay in Western Australia is one of only two places in the world where living marine stromatolites exist.
  • Importance:
    • Stromatolites provide some of the most ancient records of life on Earth by fossil remains which date back more than 3.5 billion years ago.
    • Further, these biotic structures were instrumental in the Great Oxygenation Event over two billion years ago, introducing oxygen into the atmosphere and transforming the planet's habitability.
  • Being photosynthetic, cyanobacteria produce oxygen as a by-product. Photosynthesis is the only major source of free oxygen gas in the atmosphere.
  • As stromatolites became more common 2.5 billion years ago, they gradually changed the Earth's atmospherefrom a carbon dioxide-rich mixture to the present-day oxygen-rich atmosphere.
  • This major change paved the way for the next evolutionary step, the appearance of life based on the eukaryotic cell (cell with a nucleus).

Q1: What is cyanobacteria?

These are also called blue-green algae, microscopic organisms found naturally in all types of water. These single-celled organisms live in fresh, brackish (combined salt and freshwater), and marine water. These organisms use sunlight to make their own food. In warm, nutrient-rich (high in phosphorus and nitrogen) environments, cyanobacteria can multiply quickly, creating blooms that spread across the water’s surface.

Source: The first life forms on Earth might have come from Saudi Arabia, scientists find new proof