Everything about Acritarch totally explained
Acritarchs are small organic structures found as
fossils. In general, any small, non-
acid soluble (for example non
carbonate, non-
siliceous) organic structure that can not otherwise be accounted for is an acritarch. Most acritarchs are likely the remains of single-celled organisms, especially the planktonic algae. They are found in sedimentary rocks from the present back into the
Precambrian. They are typically isolated from siliciclastic sedimentary rocks using
hydrofluoric acid but are occasionally extracted from carbonate-rich rocks. They are excellent candidates for index fossils used for dating rock formations in the
Paleozoic Era and when other fossils are not available. Because most acritarchs are thought to be marine, they're also useful for palaeoenvironmental interpretation. Acritarchs include the remains of a wide range of quite different kinds of organisms - ranging from the egg cases of small metazoans to resting cysts of many different kinds of chlorophyta (green algae). It is likely that some acritarch species represent the resting stages (cysts) of algae that were ancestral to the
dinoflagellates. The nature of the organisms associated with older acritarchs is generally not clear, though many are probably related to unicellular marine
algae. In theory, when the biological source (taxon) of an acritarch does become known, that particular microfossil is removed from the acritarchs and classified with its proper group.
Acritarchs are known from, and had achieved considerable diversity 100 million years later. Diversity crashed during the
Sturtian-Varanger glacial event around . Diversity increased again during the
Ediacaran period. Diversity declined suddenly at the end of the
Precambrian. The acritarchs show their greatest diversity during the
Cambrian,
Ordovician,
Silurian and
Devonian. The nature of some acritarchs can be identified by their structure. A few can be tentatively identified by the presence of specific chemicals associated with the fossils.
Whilst the
classification of acritarchs into
form genera is entirely artificial, it isn't without merit, as the form taxa show similar traits to genuine
taxa - for example an '
explosion' in the
Cambrian and a
mass extinction at the
end of the
Permian.
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