If every living thing died today, some estimates say that only around 1% would become fossils. Even fewer soft tissue would be preserved , making them even less likely to become fossils. These rare tissue fossils provide crucial clues about biology, evolution, and their formation remains a mystery. For example, why is it that scientists have found fossilized intestines but not a fossilized liver?
Fossils are formed when minerals replace the body parts and get buried in sediments, such as the mixture mud and seawater that covers the ocean floor. The fossil-building mineral calciumphosphate is a favorite of paleontologists because it preserves soft organs in amazing detail, sometimes down to the nuclei. This mineral can only form under certain acidity conditions. Scientists have hypothesized for decades, that the pH levels of decaying organs determine which ones are preserved.
University of Birmingham paleontologist Thomas Clements went to the fishmonger to learn more about how organs change after death. He devised a plan to destroy four delicious seabass. His team inserted pH probes into the internal organs of the fishes and then submerged them in artificial seawater to allow them to rot.
For 70 days the researchers watched the seabass bloat, shed their flesh and disintegrate into piles of bones while the probes monitored the body parts’ changing chemistry. The results, recently published in Paleontology, show that within 24 hours every organ’s acidity reached the right range for calcium phosphate to crystallize, with these conditions lasting up to five days. The team had expected to find stark differences between organs, but instead the whole carcass rotted evenly into a relatively homogeneous soup of decay by-products, held inside by the skin for up to 20 days.
This surprising result prompted researchers to look at other factors that might aid fossilization such as the levels of phosphorus in an organ’s tissues. Clements states that muscles are full of phosphate. “If the phosphate is already present, there’s a high probability that [the organ] will soon be replaced with calcium phosphate .”
” “It would have been interesting to do this also in nonfish organisms,” Victoria McCoy, a paleontologist at the University of Wisconsin-Milwaukee who was not involved with the study, says. She suggests that future research could also monitor the environment within decaying organs for other elements. Researchers could also examine whether tissue’s physical structures influence mineral formation. McCoy states that it raises more questions than if they could find organ-specific pH gradients. “But that’s what makes it so cool.”