Something peculiar has been found within the fossilized clams of the Tamiami Formation in Florida: dozens of small glass spheres rich in silica, no more than a few millimeters in size. These pearls are forged with heat and can be created by volcanic or industrial activity, but in this case, there is a big problem.
The Tamiami Formation does not contain volcanic rock, nor is it near a volcanic source. And the fossils it contains date back to the Plio-Pleistocene, between 5 million and 12,000 years ago, long before the industry entered the scene.
So what did these accounts forge? According to the researchers, it is most likely that an ancient meteorite crashed on Earth, reheated and expelled debris into the atmosphere, where it cooled and hardened forming small glass beads called microtektites, before falling back to the ground.
If they are indeed microtektites, as several lines of analysis suggest, these spheres would be the first ones found in Florida, and perhaps even the first ones found somewhere within the shell fossils.
The accounts were a pleasant surprise, discovered by accident. Earth scientist Mike Meyer of the University of Harrisburg, then a graduate of the University of South Florida, was opening the fossils in search of something completely different, namely the shells of microscopic unicellular organisms called benthic foraminifera.
During the search, however, small glass spheres continued to appear, primarily within the quahog shells of the south (Mercenary campechiensis).
"They really stood out," he said. "The grains of sand are a kind of lumps, shaped like potatoes. But I kept finding these tiny and perfect spheres."
In total, he gathered 83 of them, and kept them sitting in a box for more than a decade. Then he got some free time, and decided to take a closer look.
First Meyer had to mount the spheres, which is a difficult process because they are so small. This is usually done by licking a brush to collect the pearls with moisture (you would be surprised why it serves human saliva) and then deposit them in a small portion of glue. "I accidentally ate a couple of them," he said.
He then studied and photographed the physical properties of the spheres using optical microscopy, petrography and scanning electron microscopy (SEM) with secondary electron images. To study its composition, he used backscattered electron images and X-ray spectroscopy.
Then, he compared his results with samples of other materials, such as volcanic rock, by-products of coal ash from industrial processes and microtektites.
While it is not impossible for industrial by-products to be in the region, it is unlikely that they will enter clam fossils. Although the shells remain a little open for a while after the clam has died, they finally close tightly when the sediment on them closes them, enclosing everything that was trapped inside. This would have happened at least thousands of years before humans began the first industrial activities.
In addition, the size, shape and chemical composition were different from the particles of industrial coal ash. Nor was the particle composition likely to be volcanic. The remaining two options were cosmic spherical micrometeorites, tiny space glass balls, or microtektites.
A large abundance of sodium in the balls discarded the micrometeorites, since it is unlikely that much of the mineral survives the heating and evaporation involved in the entrance to the atmosphere.
Everything that left Meyer with the most likely candidate: microtektitas.
Which opens another mystery in turn, because the clams recovered from four different layers in the fossil bed, which means they were from four different time periods. And researchers have not yet discovered any impact site in the region that can help them rebuild history.
"It could be that they are a single tektite bed that was washed for millennia or it could be evidence of numerous impacts on the Florida Platform that we simply do not know," Meyer said.
The abundance of sodium also points to a nearby location for impact: near a rock salt or ocean reservoir, both options compatible with Florida.
Unfortunately, the quarry where clam fossils originated can no longer provide answers; It has become a housing development. Researchers have asked fossil hunters to pay attention to small glass beads.
The research has been published in. Meteorology and planetary science.