Scientists have discovered relatively large accumulations of magnetic iron particles, presumably associated with ancient bacteria, in sedimentary deposits of the Eocene epoch for the first time. Previously, it was possible to find only single magnetic nanoparticles of organic origin.
Some bacteria create tiny magnetic particles in their bodies that, when assembled in a chain inside the cell, act as an internal nanoscale compass. These magnetotactic bacteria orient themselves along the lines of force of the Earth’s magnetic field and this helps them efficiently find their way to areas with optimal levels of nutrients and oxygen.
Magneto-fossils are microscopic accumulations of such bacterial iron nanoparticles in sedimentary rocks. Since magnetotactic bacteria actively develop during periods of rapid temperature rise, magnetic fossils serve as indicators of global warming of the Earth’s climate in the past.
Usually, to detect a fossil’s magnetic particles, geologists are forced to grind large samples of ancient marine rocks, and then study the resulting powder using electron microscopy. This method is very laborious and expensive and does not always give results. In addition, this approach leads not only to the complete destruction of rock samples but also to the fossils that they could potentially contain. In other words, scientists have been looking for a new method for years.
Researchers from the United States and Austria discovered Middle Eocene sediments aged 56-34 million years for the first time. These are the remains of “giant” biological magnets in the form of needles or cylinders, the dimensions of which are about 20 times larger than typical magnetic fossils.
Quick note: Here is how magnetic fossils are distinguished in types. The conventional type includes the smallest ones which are about one-thousandth the width of a single hair, formed by bacteria. The giant magnetic fossils, like the newly discovered examples, are one-hundredth the width of a single hair and originate from living beings.
The authors have developed a new way of detecting “giant” magnetic fossils in the rock without destroying the samples, keeping the latter for other types of analyzes. The method, which they called FORC (first order reversal curve), includes finding magnetic signatures of ancient fossils using high-resolution magnetic measurements.
To date, none of the known living organisms could form such large accumulations of magnetic particles, and the authors admit that they do not yet know what organisms formed them in the past. They hope that this completely new method for identifying magnetic fossils will make it possible to find an answer to this question in the future and also completely change the methodology for similar studies.
The fossil accumulations of magnetic microorganisms found by scientists in time belong to the Paleocene-Eocene thermal maximum – a sharp global warming that occurred about 55 million years ago. This, one of the most dramatic climate changes in geological history, lasted only a few thousand years. Perhaps it was during this period that giant magnetic bacteria appeared on Earth for the first time.
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• Eisenstadt, A. (2021, February 1). New Way to Study Magnetic Fossils Could Help Unearth Their Origins.
• University of Utah. (2021, February 1). Mysterious magnetic fossils offer past climate clues.
• Wagner, C., Egli, R., Lascu, I., Lippert, P., Livi, K., & Sears, H. (2021, February 09). In situ magnetic identification of giant, needle-shaped magnetofossils in Paleocene–Eocene Thermal Maximum sediments.
• Yarlagadda, T. (2021, February 01). Massive magnetic fossils are a climate-crisis time machine.