There are long-standing controversies about recognizing microbialites in the fossil record. To some extent this revolves around definitions. Some researchers think the term stromatolite should only be used for structures undisputedly built by microorganisms, while others use it as a descriptive term applied to laminated structures regardless of how they were produced. There are also disputes about the extent to which organisms participated in the formation of stromatolite-like structures. In some structures microbial activity may play a major role in shaping the structure, whereas in others, precipitation, sedimentation, and environmental influences may be more important.
PHOTO: Structures of undoubted biogenic origin: Living thrombolites (unlaminated stromatolites) at Lake Clifton, near Mandurah, Western Australia
- Comparisons between fossil structures and undoubted living microbialites (like those at Shark Bay and Lake Clifton) are crucial in such debates.
- Rare fossil stromatolites have been found that contain preserved microbial remains showing that ancient stromatolites formed in much the same way as modern ones.
- Archean stromatolites (>2.5 billion years old) are usually highly controversial. Debate ranges around criteria such as their age, evidence for biogenicity, exclusion of contamination, conformity to expected evolutionary pathways, and the mechanisms by which the organisms lived and grew (paleobiology).
