Plants and humans have one thing in common: They both consist of a single cell containing a nucleus that serves a specialized function that benefits the entire organism. When life first emerged 4 billion years ago, it consisted of simple cells that lacked a nucleus. ProkaryotesAt least 2 billion years later, a major evolutionary change gave rise to the first cells with nuclei. EukaryotesAlgae and fungi are eukaryotes, as are plants, animals, and some single-celled organisms.
Genomic studies have shown that all eukaryotes share a common ancestor, or RekaHowever, these studies can only provide limited information about LECA's characteristics, so researchers know almost nothing about their abundance, appearance, or where they live. Scientists hope to understand the origins of LECA on Earth and determine how complex life arose on Earth and how it might arise on other planets.
A team of researchers from the Australian National University, the University of Bremen and the Strasbourg Institute of Chemistry sought to trace the oldest evidence of eukaryotes in rocks and determine when eukaryotes diverged from prokaryotes. They found that only eukaryotes Structure and function of cell membranes, It is called Sterols. So to find the oldest traces of eukaryotes, researchers went looking for these molecules in sediments that accumulated beneath the oceans, where many researchers think early eukaryotes evolved.
When cells die, they sink to the ocean floor and over time completely or partially decompose and become buried in marine sediments. When these sediments harden into sedimentary rocks, all the remains of the cells become trapped within them. These researchers believe that sterols and the molecules derived from them are Decomposition productsThese molecules remain in sediments for millions of years after cells die, so the researchers reasoned that the abundance of these molecules in sedimentary rocks should correspond to the number of eukaryotic organisms living in the oceans when the sediments formed.
To find out what sterols break down into, the researchers burned different amounts of sterols found in modern eukaryotes and analyzed the sterol breakdown products using techniques that identify organic molecules. Gas ChromatographyThe researchers compared the sterol breakdown products of modern eukaryotes with organic molecules they measured in rock samples from the Burnie Creek Formation in northern Australia, which contained petroleum that dates back about 1.7 billion years. Their goal was to test whether the rock samples contained the same molecules as the burned sterols, confirming that eukaryotic organisms were present in the oceans at that time.
The researchers found that the rock samples contained only a fraction of the molecules they measured in the burned sterols. The molecules in the rocks were responsible for stabilizing eukaryotic cell membranes against environmental stresses such as high temperatures and high salinity. The researchers explained that sterols help some modern eukaryotes survive such extreme conditions by attaching to cell membranes and making them strong and flexible, preventing cell rupture caused by external stresses.
The researchers propose that the rock sample preserved the remains of early eukaryotes that produced sterols to strengthen membranes to survive in extreme conditions. Although it is unclear whether eukaryotes produced sterols before or after the development of a nucleus, they suggest that sterols may have provided early eukaryotes with a distinct ecological advantage in adapting to extreme environmental stresses, potentially facilitating the evolution of more specialized life forms.
The team suggested that changing atmospheric conditions may also have triggered the formation and adaptation of eukaryotes. They explained that oxygen first accumulated in the atmosphere about 2.3 billion years ago, which represented a chemical stress in the environment that would have been lethal to early cells that were allergic to oxygen. However, the sterols present in the cell membranes of early eukaryotes may have helped them adapt to the changing atmosphere and develop a preference for more oxygen-rich environments.
The researchers concluded that ecological stress can fundamentally change cells, and that certain compounds unique to eukaryotes can be used to find them in ancient rock samples. In the future, the scientists plan to analyze other rock samples from Northern Australia to validate their results and look for other types of molecules that could provide information about LECA.
Post View: 79
Source: sciworthy.com
