stromatolite

From Ancient Greek στρώματα (strṓmata) (plural of στρῶμα (strôma, “layer”)) + λίθος (líthos, “stone, rock”).

1(geology) A laminated, columnar, rock-like structure constituting a large share of all fossils from 3.5 to 0.5 billion years ago, with some still being formed at present, some or all of which result from the deposit of minerals by microorganisms such as cyanobacteria.