These astonishing “magnetofossils” contain invaluable information on the climates of the past

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Researchers at the University of Utah (United States) have developed an innovative technique for detecting giant magnetofossils in marine sediments. These strange fossils are the result of as yet unknown specimens of bacteria called magnetotactics. However, the latter obviously contain valuable information on episodes of rapid warming of the Earth’s past. The results were recently published in the journal PNAS.

Some bacteria have the amazing ability to produce magnetosms. These are organelles that allow organisms possessing them to orient themselves thanks to the lines of the earth’s magnetic field. Discovered in 1975, they bear the name of magnetotactic bacteria. Researchers are studying them extensively nowadays, especially in the context of biotechnology.

The interest of magnetofossils in climatology

However, they are also of interest to climatologists. Indeed, their deposition and then fossilization in marine sediments leave a very specific trace of bacterial iron. These nano-sized magnetic particles are called magnetofossils. However, core samples have shown the presence of giant magnetofossils with exotic shapes at certain remote times, in particular between -56 and -34 million years ago when their size reached more than twenty times that of typical specimens.

Scientists have been able to associate these formations with episodes of sudden climatic warming, responsible for profound environmental disturbances. In fact, the particles would contain valuable information on nutrient availability and ocean stratification of the time. We remind you that bacteria use these kinds of biological compasses to move on the magnetic field lines. This allows them to find a level where the chemical conditions are ideal.

Various captures of magnetofossils seen by electron microscopy. Credits: Robert E. Kopp, 2007.

A non-destructive detection technique

In a new study, researchers have developed a way to identify these magnetofossils without the need to grind the samples into a fine powder by a destructive extraction technique. “ The extraction process can be long and unsuccessful, electron microscopy can be expensive, and destruction of samples means they are no longer useful for most other experiments. ”Says Courtney Wagner, lead author of the study. ” Collecting and storing these samples requires specialized personnel, equipment and planning. So we want to keep as much material as possible for further studies. “.

The new technique is based on high resolution magnetic measurements. Tested on samples from the shores of New Jersey, it showed that giant fossils had a specific magnetic signature. ” The measurements probe the reaction of magnetic particles to externally applied magnetic fields, making it possible to distinguish different types of iron oxide particles without actually seeing them »Explains Ramon Egli, co-author of the paper. Thus, no need to go through an expensive phase of destruction of the fragments.

The ability to quickly find giant magnetofossil assemblages in geological records will help identify the origin of these unusual magnetofossils “, Say the researchers in their study. ” This is important, because no known living organism today forms giant magnetofossils and we still don’t know which organizations have trained them in the past », Recount Courtney Wagner. “ The organisms that produced these giant magnetofossils are totally mysterious, but this leaves exciting avenues for future research. », Adds Ioan Lascu, co-author of the study.

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