Fossil evidence suggests the existence of cells similar to current cells in two different locations.
Introduction
It cannot be overstated that the most significant event in Earth’s history is the evolution of photosynthesis. The ability to extract energy from light freed life from the need to search for energy in its environment. With this new capability, life grew in complexity and spread into new environments, ultimately reshaping the Earth.
What are Thylakoids?
This study focuses on identifying structures called thylakoid membranes. These are groups of disk-shaped membranes that increase the surface area within the cell that can host photosynthetic protein complexes. Not all current cyanobacteria possess thylakoid membranes, but they are present in chloroplasts within plant cells.
Fossil Evidence
In search of thylakoids, researchers obtained small cell-like structures from sedimentary rocks at several sites. They made ultra-thin sections of these rocks and then conducted electron microscopy to analyze some details inside the cells. This allowed them to observe features only tens of nanometers wide.
The study found the presence of cells at two sites containing a multi-layered internal membrane characteristic of thylakoids: the Mackerdon Formation in Australia and the Grassy Bay Formation in Arctic Canada. The latter dates back over a billion years, significantly older than any previous evidence of thylakoids. However, the Mackerdon Formation dates back over 1.7 billion years, indicating that fossil evidence for these structures now stretches back 1.2 billion years earlier.
At the same time, there is no evidence of thylakoid membranes in a cyanobacterial fossil in the Democratic Republic of the Congo that dates back a billion years. As is known, there are still some types of cyanobacteria today that lack these structures, indicating that these lineages may have been separated for a long time.
Returning to the Past
Despite its particular significance, the findings are considered important mainly because of their implications. Molecular data suggest that the split between the two groups of cyanobacteria – those with thylakoids and those with internal membranes – dates back to an earlier period. There are also some suggestions that the evolution of thylakoid membranes provided the necessary boost for photosynthesis to trigger the Great Oxygenation Event, a time when oxygen levels in the atmosphere rose significantly for the first time.
By demonstrating the ability to detect thylakoid membranes despite the immense age, the researchers behind this work provide a strong impetus to verify their presence during periods of major evolutionary events. Fossil evidence may eventually catch up with genetic and chemical evidence when it comes to the evolution of photosynthesis.
Source: Nature, 2024. DOI: 10.1038/s41586-023-06896-7
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John Timmer
John is the science editor at Ars Technica. He holds a Bachelor’s degree in Biochemistry from Columbia University and a Ph.D. in Molecular and Cellular Biology from the University of California, Berkeley. When he steps away from the keyboard, he tends to look for a bicycle or a beautiful natural site to connect with his natural surroundings.
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