The secret ingredient for fossil preservation at a well-known French web site wouldn’t be present in a Julia Child cookbook. It was a sticky goo made by microalgae, researchers recommend.
An evaluation of roughly 22-million-year-old spider fossils from a fossil-rich rock formation in Aix-en-Provence, France, reveals that the arachnids’ our bodies have been coated with a tarry black substance. That substance, a form of biopolymer, was in all probability secreted by tiny algae known as diatoms that lived within the lake or lagoon waters on the historical web site, scientists report April 21 in Communications Earth & Environment.
The biopolymer didn’t simply coat the spiders’ our bodies — it pickled them. By chemically reacting with the spiders’ carbon-rich exoskeletons, the goo helped protect the our bodies from decomposition, permitting them to extra simply change into fossils, the workforce hypothesizes.
A clue that this coating may play a task in fossilization got here when the researchers, on a whim, positioned a spider fossil below a fluorescence microscope. To their shock, the substance glowed a vivid yellow-orange. “It was amazing!” says geologist Alison Olcott of the University of Kansas in Lawrence.
The fluorescent imaging painted a vivid, colourful palette onto what was in any other case a reasonably faint spider fossil, Olcott says. In the unique, she may barely inform the spider aside from the background rock. But below fluorescence, she says, the spider fossil glowed in a single coloration, the background in one other and the biopolymer in a 3rd.
That discovery — together with an abrupt halt in early 2020 to any extra fossil-collecting plans as a result of COVID-19 pandemic — swiftly shifted the main target of the workforce’s work. “Had it been normal times, this would have been a side note in a taxonomy study” classifying historical spiders, Olcott says. Instead, “I really had to explore what I had,” she provides. “It was me and these images.”
The researchers subsequent sought to determine the chemical make-up of the mysterious substance. The orange-yellow glow, the workforce discovered, comes from plentiful carbon and sulfur within the coating. “That got me thinking about sulfurization,” Olcott says.
Sulfurization is the response of natural carbon with sulfur, which kinds sturdy chemical bonds with the carbon, making it extra proof against degradation and breakdown — much like how tire producers harden rubber to make it extra sturdy. The course of requires a prepared provide of sulfur out there for bonding.
In fashionable instances, such a provide comes from the sulfur-rich gooey secretions of diatoms, microalgae discovered floating in lots of waters around the globe. When these secretions meet carbon-laden marine particles headed for the underside of the ocean, this sulfurization course of helps lock the carbon in place and probably preserve it buried within the seafloor.
Similarly, sulfurization may assist to protect delicate carbon-rich fossils, serving to them to face up to the take a look at of hundreds of thousands of years of geologic time. Olcott says. Scientists have usually famous diatoms within the fossil-bearing rock formations of Aix-en-Provence, in addition to at many comparable fossil-rich websites, she provides. “Everyone’s seeing diatoms everywhere. Thinking about that and the chemistry, I was like, ‘Wait a minute. All the pieces are here to make this chemistry happen.’”
The arachnids’ preservation may need gone like this: A lifeless spider, floating within the water column, grew to become coated within the diatoms’ sticky goo. The goo chemically reacted with the spider’s chitin exoskeleton, roughly pickling it and retaining the exoskeleton largely intact and prepared for fossilization.
That situation “makes sense based on what we know about organic sulfur cycling in modern environments so far,” says Morgan Raven, an natural geochemist on the University of California, Santa Barbara. Scientists nonetheless have rather a lot to be taught in regards to the situations that permit supplies like chitin to sulfurize, Raven says. “But this study highlights why that matters.”
For instance, if sulfurization selectively helps protect some sorts of natural matter — similar to soft-bodied fossils — that “could be a crucial filter on our fossil record, influencing what we do and don’t know about plant and animal evolution,” she provides.
This strategy of diatom-assisted sulfurization might have been at work in different fossil-rich websites throughout the Cenozoic Era, Olcott says. That span of time started 66 million years in the past, after an asteroid ended the Age of Dinosaurs, and continues to the current day. Before that period, diatoms weren’t widespread. That didn’t occur till silica-bearing grasses sprouted around the globe throughout the Cenozoic, providing a prepared supply of silica for the tiny creatures to construct their delicate our bodies (SN: 5/1/19).
It’s unknown if different biopolymer-producing algae may need helped fossilize soft-bodied creatures from even earlier, similar to throughout the flourishing of Cambrian Period life-forms starting round 541 million years in the past, Olcott says (SN: 4/24/19). “But it would be really interesting to expand this further out.”