A team of scientists from the University of Bristol found that after the cells in which they exist die, organelles continue to thrive, defeating earlier assumptions that organelles break down too quickly to be fossilized.
As described in the journal Sciences Advances, researchers have come out Bristol & # 39; s School of Earth Sciences were able to document the decay process of eukaryotic algal cells and showed that nuclei, chloroplasts and pyrenoids (organelles in chloroplasts) can persist in eukaryotic cells for weeks and months after cell death, long enough to be preserved as fossils.
Emily Carlisle, a PhD student at the Bristol School of Earth Sciences and co-author, was able to characterize the transformation of the organelles into something similar to snot. She said, “I spent several weeks photographing algal cells decaying and checking the condition of the nuclei, chloroplasts and pyrenoids. From this we could see that these organelles do not disintegrate immediately after cell death, but actually take many weeks to disintegrate. "
When life first appeared on earth, it was limited to simple bacteria. Two billion years later, a complex life arose in the form of large eukaryotic cells with membrane-bound organelles such as a nucleus and chloroplasts. The development of fungi, plants and animals followed.
However, it has proven difficult to tell exactly when a complex life arose. Previous genomic studies suggested that eukaryotic cells could have evolved 800 to 1,800 million years ago, an imprecise area that requires fossils to contain.
"The evolution of eukaryotes was an extremely important event in the history of life on Earth, but fossils from these cells are difficult to interpret," said Professor Phil Donoghue, an expert in molecular paleobiology and a co-author of the study. "Some of them have structures that could be organelles, but it has long been believed that organelles cannot be preserved because they disintegrate too quickly."
Although living eukaryotes contain large forms that are easily recognizable, early eukaryotes were predominantly single cells that were difficult to distinguish from bacterial cells.
In the past, large and intricate cell walls were used to identify early eukaryotes, but some bacteria can grow large and cell wall decorations can be lost to the devastation of time and erosion. Organelles such as nuclei and chloroplasts are not found in bacteria and would therefore be a definitive indicator of a complex life. However, it was believed that they disintegrate too quickly to be petrified.
The results of these experiments shed light on the controversial fossils of early complex life, which contain structures within cells. Dr. John Cunningham, a co-author from Bristol, said, “The structures in Shuiyousphaeridium, a fossil dating back 1,700 million years, is very similar to the nucleus. This interpretation was previously rejected because of the assumed rapid decay of the nuclei. Our decay experiments have shown that nuclei can persist for several weeks, i.e. the structures in Shuiyousphaeridium are likely cores. "
By revealing the decay patterns of organelles, the authors of the study can demonstrate the existence of a complex life 1,700 million years ago and thus help to elucidate their evolutionary history more precisely and clearly.
Source: Bristol University