Are these fossils dead, yet?

Non-living fossils and dead metaphors

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Keith S. Taber

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I was intrigued by some dialogue that was part of one of (physicist) Jim Al-Khalili's interviews for the BBC's 'The Life Scientific' series, where Prof. Al-Khalili "talks to leading scientists about their work, finding out what inspires and motivates them and asking what their discoveries might do for mankind".

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This week he was talking to Dr Judith Bunbury of St. Edmund's College and the Department of Earth Sciences at Cambridge ('Judith Bunbury on the shifting River Nile in the time of the Pharaohs'). It was a fascinating interview, and in particular discussed work showing how the Nile River has repeatedly changed its course over thousands of years. The Nile is considered the longest river in Africa (and possibly the world – the other contender being the Amazon).

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The exchange that especially piqued my interest followed an account of the diverse material recovered in studies that sample the sediments formed by the river. As sediments are laid down over time, a core (collected by an auger) can be understood to have formed on a time-line – with the oldest material at the bottom of the sample.

Within the sediment, researchers find fragments of animal bone, human teeth, pottery, mineral shards from the working of jewels…

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Dr Bunbury was taking about how changing fashions allowed the pottery fragments to be useful in dating material – or as the episode webpage glossed this: "pottery fragments which can be reliably time-stamped to the fashion-conscious consumers in the reign of individual Pharaohs".

This is my transcription of the exchange:

[JAK]: …a bit like fossil hunting
[JB]: well, I mean, we're just treating pottery as a kind of fossil
a kind of fossil, yeah, > no, absolutely >
< and it is a fossil <
yes, well quite, I can see the similarities.

Prof. Jim Al-Khalili interviewing Dr Judith Bunbury

Now Prof. Jim has a very gentle, conversational, interview style, as befits a programme with extended interviews with scientists talking about their lives (unlike, say, a journalist faced with a politician where a more adversarial style might be needed), so this exchange probably comes as close to a disagreement or challenge as 'The Life Scientific' gets. Taking a slight liberty, I might represent this as:

• Al-Khalili: your work is like fossil hunting, the pottery fragments are similar to fossils
• Bunbury: no, they ARE fossils

So, here we have an ontological question: are the pottery fragments recovered in archaeological digs (actually) fossils or not?

Bunbury wants to class the finds as fossils.

Al-Khalili thinks that in this context 'a kind of fossil' and 'like fossil hunting' are similes ("I can see the similarities") – the finds are somewhat like fossils, but are not fossils per se.

Read about science similes

So, who is right?

Metaphorical fossils

The term fossil is commonly used in metaphorical ways. For example, for a person to be described as a fossil is to be characterised as a kind of anachronism that has not kept up with social changes.

The term also seems to have been adopted in some areas of science as a kind of adjective. One place it is used is in relation to evidence of dampened ocean turbulence,

"The term 'fossil turbulence' refers to remnants of turbulence in fluid which is no longer turbulent."

Gibson, 1980, p.221

If that seems like a contradiction, it is explained that

"Small scale fluctuations of temperature, salinity, and vorticity in the ocean occur in isolated patches apparently caused by bursts of active turbulence. After the turbulence has been dampened by stable stratification the fluctuations persist as fossil turbulence."

Gibson, 1980, p.221

So, 'fossil turbulence' is not actually turbulence, but more the afterglow of the turbulence: a bit like the aftermath of a lively party which leaves its traces: the the chaotic pattern of abandoned debris provides signs there has been a party although there is clearly no longer a party going on.

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Another example from astronomy is fossil groups of galaxies, which are apparently "systems with a very luminous X-ray source …and a very optically dominant central galaxy" (Kanagusuku, Díaz-Giménez & Zandivarez, 2016). It seems,

"The true nature of fossil groups in the Universe still puzzles the astronomical community. These peculiar systems are one of the most intriguing places in the Universe where giant elliptical galaxies are hosted [sic]."

Kanagusuku, Díaz-Giménez & Zandivarez, 2016

('Hosted' here also seems metaphorical – who or what could be acting as a host to an elliptical galaxy?)

The term 'fossil group' was introduced for "for an apparently isolated elliptical galaxy surrounded by an X-ray halo, with an X-ray luminosity typical of a group of galaxies" (Zarattini, Biviano, Aguerri, Girardi & D'Onghia, 2012): so, something that looks like a single galaxy, but in other respsects resembles a whole group of galaxies?

Close examination might reveal other galaxies present, yet the 'fossil' group is "distinguished by a large gap between the brightest galaxy and the fainter members" (Dariush, Khosroshahi, Ponman, Pearce, Raychaudhury & Hartley, 2007). Of course, there is normally a 'large gap' between any two galaxies (space contains a lot of, well, space), but presumably this is another metaphor – there is a 'gap' between the magnitude of the luminosity of the brightest galaxy, and the magnitudes of the luminosities of the others.

Read about science metaphors

Dead metaphors

One way in which language changes over time is through the (metaphorical) death of metaphors. Terms that are initially introduced as metaphors sometimes get generally adopted and over time become accepted terminology.

Many words in current use today were originally coined in this way, and often people are quite unaware of their origins. References to the hands of a clock or watch will these days be taken as simply a technical term (or perhaps for those who only familiar with digital clocks, a complete mystery?) In time, this may happen to 'fossil turbulence' or 'fossil galaxy groups'.

What counts as a fossil?

But it seems reasonable to suggest that, currently at least, these are still metaphors, implying that in some sense the ocean fluctuations or the galactic groups are somewhat like fossils. But these are not actual fossils, just as tin-pot dictators are not actually fabricated from tin.

So, what are actual fossils. The 'classic' fossil takes the form of an ancient, often extinct, living organism, or a part thereof, but composed of rock which has over time replaced the original organic material. In this sense, Prof. Al-Khalili seems correct in suggesting bits of pottery are only akin to fossils, and not actually fossils. But is that how the experts use the term?

According to the British Geological Survey (BGS):

Fossils are the preserved remains of plants and animals whose bodies were buried in sediments, such as sand and mud, under ancient seas, lakes and rivers. Fossils also include any preserved trace of life that is typically more than 10 000 years old. 

https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/fossils/ ¹

Now, pottery is not the preserved remains of plants or animals or other living organisms, but the site goes on to explain,

Preserved evidence of the body parts of ancient animals, plants and other life forms are called 'body fossils'. 'Trace fossils' are the evidence left by organisms in sediment, such as footprints, burrows and plant roots.

https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/fossils ¹

So, footprints, burrows, [evidence of] plant roots ²…or shards of pottery…can be trace fossils? After all, unearthed pottery is indirect evidence of living human creatures having been present in the environment, and, as the BGS also points out "the word fossil is derived from the Latin fossilis meaning 'unearthed'."

However, if the term originally simply meant something unearthed, then although the bits of pot would count as fossils – based on that argument so would potatoes growing in farmers' fields. So, clearly the English word 'fossil' has a more specific meaning in common use than its Latin ancestor.

But going by the BGS definition, Dr Bunbury's unearthed samples of pottery are certainly evidence of organisms left in sediment, so might be considered fossils. These fossils are not the remains of dead organisms, but neither is 'fossil' here simply a metaphor (not even a dead metaphor).

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Work cited:

• Dariush, A, Khosroshahi, H. G., Ponman, T. J., Pearce, F., Raychaudhury, S. & Hartley, W. (2007), The mass assembly of fossil groups of galaxies in the Millennium simulation, Monthly Notices of the Royal Astronomical Society, Volume 382, Issue 1, 21 November 2007, Pages 433-442, https://doi.org/10.1111/j.1365-2966.2007.12385.x
• Gibson, Carl H. (1980) Fossil Temperature, Salinity, and Vorticity Turbulence in the Ocean. In Jacques C.J. Nihoul (Ed.) Marine Turbulence, Elsevier, pp. 221-257.
• Kanagusuku, María José, Díaz-Giménez, Eugenia & Zandivarez, Ariel (2016) Fossil groups in the Millennium simulation – From the brightest to the faintest galaxies during the past 8 Gyr, Astronomy & Astrophysics, 586 (2016) A40, https://doi.org/10.1051/0004-6361/201527269.
• Romero, I. C., Nuñez Otaño, N. B., Gibson, M. E., Spears, T. M., Fairchild, C. J., Tarlton, L., . . . O'Keefe, J. M. K. (2021). First Record of Fungal Diversity in the Tropical and Warm-Temperate Middle Miocene Climate Optimum Forests of Eurasia [Original Research]. Frontiers in Forests and Global Change, 4. https://doi.org/10.3389/ffgc.2021.768405
• Zarattini, S., Biviano, A., Aguerri, J. A. L., Girardi, M. & D'Onghia, E. (2012) Fossil group origins – XI. The dependence of galaxy orbits on the magnitude gap, Astronomy & Astrophysics, 655 (2021) A103, DOI: https://doi.org/10.1051/0004-6361/202038722.

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Notes:

¹ "Fossils are the preserved remains of plants and animals whose bodies …". But this suggests that fungi do not form fossils. The same site points out that "We tend to think of fungi, such as mushrooms and toadstools, as being plants — but they are not. They neither grow from embryos nor photosynthesise and are put in a separate kingdom" (https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/plants-2/) – yet does not seem to mention any examples of fungi that have been fossilised (so the comment could be read to be meant to suggest that fossil fungi are found as well as fossil plants; but could equally well be read to mean that as fungi are not plants they do not fossilise).

The second quote here is more inclusive: "Preserved evidence of the body parts of ancient animals, plants and other life forms…" The site does also specify that "Remains can include microscopically small fossils, such as single-celled foraminifera…" (https://www.bgs.ac.uk/discovering-geology/fossils-and-geological-time/fossils/).

So, just to be clear, fossil fungi have been found.

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² If the roots were themselves fossilised then these would surely be body fossils as roots are parts of plant. Presumably this is meant to refer to the channels in soil when the roots grow through the soil.

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