Researchers Find 2-3-Million-Year-Old Microtektites inside Fossil Clams

Wednesday, July 24, 2019

A microtektite from the shell bed of southwestern Florida. Image credit: Meyer et al, doi: 10.1111/maps.13299.

Fossil clams found in southwestern Florida contain ancient microtektites, tiny (about 200 μm in diameter) glass beads that form when the explosive impact of an extraterrestrial object sends molten debris hurtling into the atmosphere where it cools and recrystallizes before falling back to Earth.

Dr. Mike Meyer, a researcher at Harrisburg University in Pennsylvania, and colleagues found 83 glassy spheres inside fossil clams from a quarry in Sarasota County, Florida.

“We were looking for the shells of single-celled organisms known as benthic foraminifera, when we noticed the translucent glassy balls, smaller than grains of salt,” Dr. Meyer explained.

“They really stood out. Sand grains are kind of lumpy, potato-shaped things. But I kept finding these tiny, perfect spheres.”

The scientists analyzed the elemental makeup and physical features of the spheres and compared them to other microtektites, volcanic rock and byproducts of industrial processes, such as coal ash.

According to the team, these microtektites are between 2 and 3 million years old.

They are likely the remnants of one or more undocumented meteor impacts on or near the Florida Platform, the plateau that undergirds the Florida Peninsula.

“Initial results from an unpublished test suggest the spheres have traces of exotic metals, further evidence they are microtektites,” said Dr. Meyer, lead author of a paper published in the journal Meteoritics & Planetary Science.

“One oddity is that they contain high amounts of sodium, a feature that sets them apart from other impact debris. Salt is highly volatile and generally boils off if thrust into the atmosphere at high speed.”

“This high sodium content is intriguing because it suggests a very close location for the impact.”

“Or at the very least, whatever impact created it likely hit a very large reserve of rock salt or the ocean. A lot of those indicators point to something close to Florida.”

The researchers suspect there are far more microtektites awaiting discovery in Florida and asked amateur fossil collectors to keep an eye out for the tiny spheres.


Mike Meyer et al. A first report of microtektites from the shell beds of southwestern Florida. Meteoritics & Planetary Science, published online May 6, 2019; doi: 10.1111/maps.13299