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Ethereal & # 39; beads & # 39; in fossil shells testify to an ancient meteorite that hits the earth



Something special was found in fossil shellfish from the Tamiami Formation in Florida: dozens of tiny, silica-rich glass spheres no larger than a few millimeters in diameter. Such beads are forged by heat and may be caused by volcanic or industrial activities – but in this case there is a big problem.

The Tamiami Formation contains neither volcanic rock nor is it near a volcanic source. And the fossils it contains come from the Plio-Pleistocene, which was between 5 million and 12,000 years old – long before the industry came on the scene.

So, what did these pearls forge? According to the researchers, it was most likely an ancient meteorite that hit the earth, heated itself and threw debris into the atmosphere where it cooled and hardened into tiny glass beads, the so-called microtectites, before falling back to the ground.

Microtectites, as several analyzes show, would make these bullets the first to be found in Florida, and perhaps even the first ever found in mussel fossils.

The pearls were a delightful surprise that was discovered by accident. Harrisburg University geoscientist Mike Meyer ̵

1; then a student at the University of South Florida – praised the fossils in search of something completely different, namely the shells of microscopic single-celled organisms, the benthic foraminifera.

Small glass spheres appeared again and again, mostly in southern quahog shells ( Mercenaria campechiensis .

 other microtectites (Meyer et al., Meteoritics and Planetary Science, 2019)

"They really stood out," he said, "grains of sand are kind of lumpy, potato-shaped things, but I've always found those tiny, perfect orbs."

Overall He collected 83 of them and left them lying in a box for more than a decade, then had some free time and decided to take a closer look.

First, Meyer had to assemble the balls, which is a difficult process because they did This is usually done by licking a brush to pick up the beads with moisture (you would be surprised what human saliva is good for), and then apply glue to a small patch of glue. "I accidentally ate some," he said.

He then studied and photographed the physical properties of the spheres using light microscopy, petrography and scanning electron microscopy (SEM) with secondary electron imaging. To study their composition, he used REM backscattered electron imaging and X-ray spectroscopy.

 Microtektite (Meyer et al., Meteoritics and Planetary Science, 2019)

Then he compared his findings to samples of other materials, including volcanic rock, industrial coal residue Processes and microtectites.

While it is not impossible that industrial residues could be present in the region, they are unlikely to work their way into the shell fossils. Even if the shells remain slightly open for some time after the shell's death, they finally close while sediment above them crushes them and locks in everything that was trapped inside. This would have happened at least a thousand years before humans began their first industrial activities.

In addition, size, shape and chemical composition were different from those of industrial carbonaceous particles. Nor was it likely that the composition of the particles was volcanic. The two remaining options were micrometeorites with cosmic beads – tiny glass spheres from space – or microtectites.

High levels of sodium in the spheres ruled out micrometeorites as it was unlikely that much of the mineral survived the warming and evaporation of atmospheric entry.

All that Meyer left behind with the most likely candidate: microtectites.

Which, in turn, solves another puzzle because the shells of four different layers were recovered in the fossil bed, meaning that they came from four different periods. And researchers have not yet discovered any impact points in the region that could help them put the story together.

"It could be that they come from a single tctit bed that has been washed out for millennia, or it could be evidence of numerous impacts on the Florida platform of which we know very little," Meyer said.

Unfortunately, the quarry from which the shell fossils originate can no longer provide answers; It was turned into a housing estate. Researchers have asked fossil hunters to look for tiny glass beads.

The research was published in Meteoritics and Planetary Science .


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