What are acritarchs
Among the oldest micro-organisms, acritarchs are one of them. Acritarchs are organic-walled microfossils that range in size from 20- 80 micrometers. They are widely distributed from the Archean age of 3000 million years to the recent. Acritarchs are the most important microfossils among geologists because of their long geologic history of the existence.
Geologist tries to find the correlation between the first life on the earth with this type of unicellular micro-organism to convey the link between human micro-organisms from the past to the present. Through the study of acritarchs, a scientist can explore the paleoenvironment of the earth.
Acritarchs are the unicellular, organic-walled micro-organism of unknown origin. They usually fall in the group of dinoflagellates. Because they are usually found in the rock along with the dinoflagellates type of microorganisms. They have a spike or ornamentation on their wall. Based on the spike and the shape of the acritarchs scientist can classify the acritarchs. Acritarchs are usually 20- 80 microns in size. So they can not be seen with the naked eye. Acritarchs are the most rigid and undegradable unicellular micro-organisms.
It is a non-carbonate, non-silicious, and non-acid soluble organism. So, in the rock sample, it is a very nicely preserved organism. It is very important for the geologist to explore the paleo-environments of the earth. The acritarchs first appeared in the Proterozoic and reached the maximum in the Early to Middle Paleozoic.
In the Carboniferous and Permian, they are nearly absent and the sudden absence of the acritarchs is called the “Phytoplankton Block Out”. Some scientists they try to reveal the similarity between the acritarch and the phytoplankton. Based on the value of the Carbon 13 of acritarchs and the Phytoplankton they found a similar value. Hence they emphasized that it may be in the phytoplankton type of microorganism. But still, the exact origin of acritarchs is unraveled!
How to Classify the Acritarch?
Based on the ornamentation and the geometrical shape of the vesicle of acritarchs, they can be classified into five different types. In a study from South China, Shangsi, Meishan, and some other section, geologists and paleontologists found a wide variety of acritarchs preserves in the samples. The Micrhystridium, Veryhachium type of acritarchs are very small in size usually 20 micrometers.
The classifications are;
- The Veryhachium cylindricum group: This group represents all the ellipsoidal shapes of the Acritarchs.
- The Veryhachium trispinosum group: This group includes all triangular-shaped vesicles.
- The Veryhachium lairdii group: This Group includes all rectangular forms of the acritarchs.
- The Micrhystridium pentagonale group: This group covers all the pentagonal shapes fo the acritarchs.
- The Micrhystridium breve group: This group includes all the spherical forms of acritarchs.
What is Known So Far About the Unknow-Origin of Acritarchs?
Acritarchs are sometimes called the phytoplankton origin of organisms. So, Phytoplankton and acritarchs may have relationships. But before the final discovery of the exact origin of acritarchs still, there is a huge debate among geologists, paleontologists, and other scientists.
- They are mainly marine phytoplankton or algae or unknown affinities of origin. Grice et al. (2005) state that similar values of stable carbon isotopic composition of the acritarchs derived biomarker (Geochemical fossils) and phytane sourced from chlorophyll a in phytoplankton
- Another potential source was reported in cold-seep carbonate crusts (Pancost et al., 2001).
- A series of linear diphenyl alkanes have been reported in sulfur-rich coals containing biomarkers also derived from Chlorobiaceae (Gorchs et al., 2003).
- Some suggested that it might be derived from an organism that inhabited in a sulfide-rich environment (Grice et al., 2005; Fig. 15).
Though it is still a huge scope for the geologist to discover the exact sources of the acritarch in the Permian rocks or other older rocks to explore the paleo-history of the earth and can be linked up with the great mass extinction of the earth. During the last five mass extinction events, (Ordovician-Silurian, Devonian-carboniferous, Permian Triassic, Triassic Jurassic, and the last Cretaceous Paleogene mass extinction) this micro-organism had been survived and experienced and until today we can find acritarchs in the recent sample.
The distribution of acritarchs in the geologic past:
Acritarchs are a type of microfossil that were present in various ancient sediments. Acritarchs lived in different environments such as island and oceanic waters and served as food for all kinds of organisms.
Different types of acritarchs and their presence were notable in various ancient sediments. The most reliable and widespread acritarchs are known to exist in the Cambrian era. Acritarchs of other types were also present in even more ancient sediments such as the Ordovician and Silurian periods.
The abundance of acritarchs may be associated with the Cambrian period, as it was first recorded during this time. During this period, the presence of acritarchs was prominent in sediments around the world.
Are acritarchs eukaryotes?
What do acritarchs represent?
Is an Acritarch a bacteria?
What is the Acritarch morphology?
Acritarchs are not definitively classified as either eukaryotes or prokaryotes, as they are not complete cells but rather organic-walled microfossils. However, many researchers consider them to be eukaryotic in nature, based on their complex morphologies.
Acritarchs represent the organic-walled remains of a diverse group of unicellular organisms that lived in various aquatic environments in the past. They have been found in rocks that date back to as early as 3 billion years ago and are used by scientists as a tool for dating and correlating rocks of similar age.
Acritarchs are not bacteria. They are thought to be the remains of a diverse group of unicellular organisms that have an uncertain taxonomic affinity, which means they do not clearly belong to any known group of organisms.
The morphology of acritarchs varies widely and can be complex. They can be spherical, elliptical, or spindle-shaped, and can have a variety of surface ornamentations and internal structures. Some acritarchs have distinctive spines, horns, or other projections, while others are smooth and featureless. The wide range of morphologies seen in acritarchs is one of the reasons why they are difficult to classify taxonomically.
|Taxonomy||Uncertain; may represent a diverse group of unicellular eukaryotes|
|Age range||3 billion years ago to present|
|Morphology||Spherical, elliptical, or spindle-shaped; can have surface ornamentations and internal structures; some have spines, horns, or other projections|
|Abundance||Widespread in various ancient sediments|
|Use||Tool for dating and correlating rocks of similar age|
|Environmental||Lived in various aquatic environments such as island and oceanic waters|
|Food source||Served as food for all kinds of organisms|
|Significance||Provides evidence of ancient life; helps to understand the evolution and diversification of eukaryotes|
|Challenges||Difficult to classify taxonomically due to the wide range of morphologies seen in acritarchs|
|Importance||Acritarchs are valuable for studying the evolution and diversification of eukaryotes, as they provide evidence of ancient life|
So, Acritarchs can live in stressful environments and are able to survive the event in the extinction span of time. Hence, we need more work on acritarchs to explore the past based on micro-fossils.