Microbial mats

1.3 billion-year old stromatolite. It is formed by
many layers of fossilized microbial mats
As long as microorganisms were the only living beings on earth - for about three billion years, microbial mats were abundant worldwide. Today, one can find them only at places where they are not destroyed by grazers. However, one can find their lithified residues as stromatolites, which means 'pillow stones'.

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