2023-12-13 07:00:00
The black chert sedimentary rock from which the mysterious microfossils of Earth’s early history were extracted. Credit: Erica Barlow Stephanie Leonida Meteored United Kingdom 13/12/2023 08:00 6 min
Research carried out by an international team of researchers details microfossil evidence suggesting that complex eukaryotic life appeared on Earth earlier than previously thought.
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Erica Barlow, associate research professor in the Department of Geosciences at Pennsylvania State University, discovered the microfossils in a type of sedimentary rock called black chert. Delving deeper into this ancient snapshot of Earth’s history has led to more questions regarding the evolution of life on Earth. The researchers published their findings in the journal Geobiology.
The Great Oxidation Event
The Great Oxidation Event (GOE) occurred approximately 2.4 million years ago and oxygen levels increased significantly due to the appearance and spread of cyanobacteria. These bacteria produce oxygen as a byproduct through a vital process called photosynthesis.
The Great Oxidation Event (GOE) was a time interval in which Earth’s atmosphere and shallow ocean first experienced an increase in the amount of #oxygen. This occurred approx. 2.4-2.0 Ga (billion years) during the Paleoproterozoic era. pic.twitter.com/0M9gmAnnbL
— Jose Luis Vega (@jlu_vega) December 6, 2021
The buildup of oxygen in the atmosphere has transformed Earth’s geology and biological inhabitants. It caused mineral oxidation on the earth’s surface, resulting in the production of new minerals and the accumulation of iron oxides. One of the geological indicators of GOE is the widespread “oxidation” of iron.
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Although increased atmospheric oxygen has benefited aerobic (oxygen-dependent) creatures, it was likely devastating to the many anaerobic (non-oxygen-dependent) life forms that had previously dominated the planet. This event set the course of Earth’s biosphere, favoring organisms adapted to living in a highly oxygenated environment.
The origin of life on Earth
The general consensus among the scientific community is that prokaryotic life forms (e.g. archaea and bacteria) appeared before more complex eukaryotic life forms.
Compared to modern organisms, #PennState researchers with @GeoscPSU say microfossils more closely resemble a type of algae than simpler prokaryotic life organisms like bacteria, for example that existed before the “Great Oxidation Event”: pic.twitter.com/6XC7WhWUAP
— Penn State Research (@PSUresearch) November 14, 2023
Unlike prokaryotic cells, eukaryotic cells have what is called a true nucleus, an area containing linearly structured DNA enclosed in a nuclear membrane. Eukaryotes (such as fungi, plants, algae and animals) also have membrane-bound organelles, subcellular structures that are responsible for carrying out essential tasks to support proper cellular function.
“A great affirmation”
Researchers examined microfossils and observed that they were indeed larger than other microfossils dating from before the GOE event. The team also observed their spherical aggregate morphology, something that had not previously been seen in the fossil record.
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“I think finding a fossil that is so large and complex, relatively early in the history of life on Earth, makes one wonder: “If we find life elsewhere, it might not just be prokaryotic bacterial life.” Professor Barlow said. “Perhaps there is the possibility that something more complex is preserved; even if it’s still microscopic, it might be something of a slightly higher order.”
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The first major extinction event on earth was known as the great oxidation event and occurred as a result of increased O2 in the atmosphere
(thread) pic.twitter.com/SoG0ihR1Rn
— CK (@photobiogenesis) December 15, 2021
Barlow explains that the microfossils share similarities with modern green algae in the Volvocaceae family. “This suggests that the fossil is possibly a primitive eukaryotic fossil. This is a big statement and something that needs more work, but it raises an interesting question that the community can develop and test.”
Further research is needed to determine whether the microfossils were left behind by eukaryotic species, but the idea has important consequences, experts say. As a result, the known record of eukaryotic microfossils would advance by 750 million years.
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