Their soft outer skeletons typically do not retain well – except in a few extraordinary places around the world. There is a remarkable place in the south of France where fossils of spiders that last spun a web 22.5 million years ago have been discovered.
Scientists said they have found out why so many soft creatures like spiders, insects and fish are buried and preserved so detailed by this particular rock formation in Aix-en-Provence. The very favorable conditions involve a substance produced by microalgae, which would have coated the spider and promoted a protective chemical change.
“Most life does not become a fossil,” Alison Olcott, associate professor of geology and director of the Center for Undergraduate Research at the University of Kansas, said in a news release.
“It’s hard to become a fossil. You have to die under very specific circumstances, and one of the easiest ways to become a fossil is to have hard parts like bones, horns and teeth. So, our record of soft body life and terrestrial life, like spiders, are spotted, “said Olcott, lead author of the study, published in the journal Communications Earth & Environment.
“But we have these periods of exceptional conservation, where all circumstances were harmonious for conservation to happen.”
Fluorescence gives traces
The discovery was made thanks to a decision to examine the spider fossil under a fluorescent microscope, Olcott said in the release. This type of observation is not part of the standard protocol for the study of fossils, but the research team thought it could help them distinguish more details about the fossilized spiders that mingled in the surrounding rock. Different elements in the rock absorb the energy from the UV light in the microscope and remit light at different wavelengths.
“To our surprise, they glowed, and therefore we became very interested in what the chemistry of these fossils was that made them glow. If you just look at the fossil on the rock, they can hardly be distinguished from the rock itself, but they glowed another color under the fluorescent scope. ”
Not all geological samples are autofluorescent and light – but when they are, it can be spectacular and provide a lot of information, Olcott said. The microscopic aquatic algae detected by fluorescent microscopes are known as diatoms fossils, and when alive, they secrete sulfur-rich substances that form algae mats.
“These microalgae make the sticky, viscous gloop – that’s how they stick together,” she said.
The authors suggested that this substance covered the spiders and improved a process called sulfur formation, which stabilized and preserved the fragile bodies of the spiders.
“Basically, the chemistry of microalgae and the chemistry of spiders work together to make this unique conservation happen,” she said.
Olcott said the discovery could help geologists identify other unusual fossil sites from this time period in other parts of the globe.
“If diatomaceous earth mats really help to evoke this exquisite fossil conservation, then we should be able to further explore diatoms units, the diatoms-rich rocks found globally at this time, to look for more of these deposits.