What are stromatolites?
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Stromatolites are rock-like structures of multi-layered sheets of microorganisms (microbial mats) that form in limestone. Stromatolites generally form from the trapping and binding of particles by microorganisms e.g. algae and bacteria, and grow upward to get light from photosynthesis. Stromatolites provide scientists with some of the oldest records of early life on earth found from fossil remnants dating back to more than 3.5 billion years ago. Name the organism that forms Stromatolites and how they form them: Cyanobacteria form’s Stromatolites from the Cyanobacteria forming ‘colonies’, trapping sediments with their sticky surface. The sediment, now trapped, reacts with calcium carbonate in the water which creates limestone. The limestone starts to build up slowly; i.e. it can take a Stromatolite, approximately, 100 years to grow five cm until it reaches its full height.
Diagram of Stromatolite formation:
The main features of the environment occupied by Stromalite Cyanobacteria Stromatolite Cyanobacteria, due to being photosynthetic requires the water to be shallow, so they can reach the bottom of the ‘water column’ and to have water currents to provide them with the right amount of silt for the stromatolites to cement the silt with the limestone they get from the water, without being overwhelmed by the silt. Stromatolites can exist in places very few life forms can tolerate. For example, they can be found today in hyper-saline lakes and aquatic environments where the salt level is so high, it stops most other life using them.
The role of Stromatolite bacteria in its environment
Stromatolites are able to make their own food through the process of photosynthesis, using chlorophyll. They absorb carbon dioxide from the atmosphere, using the energy retained to build it into energy containing sugars, while they release oxygen. Millions of years ago, the
photosynthesis carried out by the Stromatolites, managed to consume most of the carbon dioxide present, and release enough oxygen to make permanent changes in the atmosphere.
Diagram of process:
The similarities in the past and present environments for Stromatolite Cyanobacteria Outline whether they live in and support anoxic conditions, or live and support oxic conditions From the beginning of Archean times (approx 3.5 billion years ago), Stromatolites began to range in diversity due to the atmosphere changing from having no oxygen to having oxygen, allowing stromatolites to further diversify. Due to this, there was a transition to marine environments with large continental shelves that provided the Stromatolites with a wider habitat. Studies have shown Cyanobacteria to be the contributing factor to of the atmospheric change from anoxic to oxic conditions. As Stromatolites are photosynthetic, they respire during the day, aerobically, but without light, they can also withstand anaerobic conditions. Stromatolites past living conditons consisted of hostile environments i.e. very salty or acidic waters, and coastal habitats. Today, Stromatolites have been found in a diverse range of conditions and habitats, though are predominantly, still living in extreme environments
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