Scientists have long puzzled over the exceptional preservation of certain fossils of Cenozoic-era biota, including plants, fish, amphibians, spiders, and other insects. The secret: The presence of mats comprised of single-celled microalgae (diatoms) created an anaerobic environment for fossilization and chemically reacted with the spiders’ organic polymers to turn them into thin carbon-rich films. The process is similar to a common industrial treatment to preserve rubber, according to a recent paper published in the journal Communications Earth & Environment.
Most fossils are basically mineralized body parts: shells, bones, and teeth. But softer tissues are far more likely to decay than fossilize, including chitinous exoskeletons, skin, and feathers. Soft-tissue organisms tend to be under-represented among fossils, except for unusual deposits (called Fossil-Lagerstätten) that boast rich arrays of such fossils in remarkable preservation.
“Most life doesn’t become a fossil,” said Alison Olcott, a geologist at the University of Kansas. “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, is spotty—but we have these periods of exceptional preservation when all circumstances were harmonious for preservation to happen.”
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