The fossilised remains of Keuppia, an extinct genus of octopus alongside an artist's impression of what the animal may have looked like
Credit (left): Jonathan Jackson/NHMUK
Credit (right): Smokeybjb, CC BY-SA 3.0, via Wikimedia.
Credit (right): Smokeybjb, CC BY-SA 3.0, via Wikimedia.
As anyone who frequents social media Creationism vs Science groups will be familiar, Creationists love fossilised 'soft' tissue, which they claim shows Earth is just a few thousand years old because soft tissue would have rotted away before now if Earth really is billions of years old, like scientists say. Some Creationists will even try to pad out their soft tissue 'argument' with the lie that such fossils have been subjected to carbon 14 dating and found to be just a few thousand years old, forgetting for the moment that Creationist dogma requires that all radiometric dating techniques must be dismissed as fake because "radiometric (read C14) dating is a flawed concept, because it doesn’t work for anything older than 50,000 years".
It is, of course, nonsense, because what these so-called soft-tissue fossils are not, is soft. They are hard fossils of what had been soft tissue just as hard-tissue fossils are hard fossils of what had been hard tissue. The question for science was not why they are still soft, but how soft tissues, in certain rare conditions, remained intact and with such detail preserved for long enough to be replaced by minerals. In particular, why do some internal organs fare better than others in that process?
Now a team of scientists from Leicester University, UK, believe they have answered that by following the process of decay in a fish. The answer is to do with the pH of the tissue as it decays, which affects how readily it can be replaced with calcium phosphate, or apatite. As the news release from Leicester University explains:
Researchers in Leicester’s Centre for Palaeobiology developed an experiment to study the chemistry inside a decaying fish and map the pH levels of its internal organs over the course of the carcass decaying for two-and-a-half months.
Their findings, published today (Monday [08 August 2022]) in Palaeontology, show that each organ’s specific tissue chemistry governs its likelihood to be replaced by minerals.One of the best ways that soft tissue can turn into rock is when they are replaced by a mineral called calcium phosphate (sometimes called apatite). Scientists have been studying calcium phosphate for decades trying to understand how this process happens - but one question we just don’t understand is why some internal organs seem more likely to be preserved than others.
We designed an experiment observing rotting fish which was disgusting and smelly, but we made an interesting discovery.
The organs don’t generate special microenvironments – they all rot in a kind of ‘soup’ together. This means that it is the specific tissue chemistry of the organs that governs their likelihood to turn into fossils.
Dr Thomas Clements, Senior author
Formerly PhD candidate, Leicester University, UK Now with University of Birmingham, UK
This result explains why some tissues are more easily turned into the calcium phosphate fossils which capture high-resolution detail of a creature’s most fragile material, while other organs are seemingly lost to time.
The fossilised remains of Keuppia, an extinct genus of octopus, held in the Natural History Museum's collections.
Credit: Jonathan Jackson/NHMUK.Dr Thomas Clements, now of the University of Birmingham, led the study during his time as a PhD researcher at Leicester.Watching and recording (and smelling) how a fish rots may not be most people’s idea of science, but for palaeontologists understanding the process of decay is crucial to revealing which anatomical features of an animal are likely to become a fossil, and what they will look like.
We were really pleased with the results because we can now explain, for example, why fossils often preserve an animal’s gut but never preserve their liver.
Professor Sarah Gabbott, co-author Professor of Palaeobiology
Centre for Palaeobiology & Biosphere Evolution
School of Geography, Geology and the Environment
University of Leicester, Leicester, UK
In order for a tissue to phosphatize, its pH must fall below about pH 6.4. At this acidity, if the fossil is buried quickly, calcium phosphate and other minerals can begin the fossilisation process which preserves the exquisite detail of some soft tissues.
One of the finest examples of such fossils includes a Cretaceous-era octopus of the extinct genus Keuppia unearthed in Lebanon, estimated to be at least 94 million years old.
AbstractIt would be nice now not to have to keep refuting the Creationist 'soft tissue' lie, but to a Creationist, having a lie refuted is never regarded as a good reason not to try to get away with it in a different group. There is no commitment to truth in Creationism.
Replacement of soft tissues by calcium phosphate can yield spectacular fossils. However, in the fossil record, the phosphatization of internal organs is highly selective; some internal organs, such as muscles, stomachs, and intestines, appear to preferentially phosphatize while other organs seldom phosphatize. The reasons for this are unclear but one hypothesis is that, during decay, organs create distinct chemical microenvironments and only some fall below the critical pH threshold for mineralization to occur (i.e. below the carbonic acid dissociation constant: pH 6.38). Here, we present a novel investigation using microelectrodes that record dynamic spatial and temporal pH gradients inside organs within a fish carcass in real time. Our experiments demonstrate that within a decaying fish carcass, organ-specific microenvironments are not generated. Rather, a pervasive pH environment forms within the body cavity which persists until integumentary failure. With no evidence to support the development of organ-specific microenvironments during decay our data suggest other factors must control differential organ phosphatization. We propose, that when conditions are amenable, it is tissue biochemistry that plays an important role in selective phosphatization. Tissues with high phosphate content (and those rich in collagen) are most likely to phosphatize. Internal organs that typically have lower tissue-bound phosphate, including the integuments of the stomach and intestine, may require other sources of phosphate such as ingested phosphate-rich organic matter. If tissue biochemistry is the driver behind selective phosphatization, this may provide insights into other highly selective modes of soft-tissue preservation (e.g. pyritization).
Clements, T., Purnell, M.A. and Gabbott, S. (2022)
Experimental analysis of organ decay and pH gradients within a carcass and the implications for phosphatization of soft tissues.
Palaeontology, 65: e12617. DOI: 10.1111/pala.12617
Copyright: © 2022 The authors.
Published by John Wiley & Sons, Inc. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
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