Fossils are invaluable archives of the previous. They protect particulars about residing issues from just a few thousand to tons of of hundreds of thousands of years in the past.
Learning fossils might help us perceive the evolution of species over time, and glimpse snapshots of previous environments and climates. Fossils also can reveal the diets or migration patterns of long-gone species – together with our personal ancestors.
However when residing issues flip to rock, discerning these particulars isn’t any simple feat. One widespread approach for finding out fossils is micro-computerised tomography or micro-CT. It’s been used to seek out the earliest proof of bone most cancers in people, to check mind imprints and inside ears in early hominins, and to check the enamel of the oldest human trendy stays outdoors Africa, amongst many different examples.
Nonetheless, our new examine, revealed right this moment in Radiocarbon, exhibits that regardless of being extensively considered non-destructive, micro-CT may very well have an effect on fossil preservation and erase some essential info held inside.
Preserving treasured specimens
Fossils are uncommon and fragile by nature. Scientists are continually evaluating how one can steadiness their influence on fossils with the necessity to examine them.
When palaeontologists and palaeoanthropologists (who work on human fossils) analyse fossils, they need to minimise any potential harm. We need to protect fossils for future generations as a lot as doable – and know-how could be a large assist right here.
Micro-CT works just like the medical CT scans medical doctors use to peek contained in the human physique. Nonetheless, it does so at a a lot smaller scale and at a better decision.
That is excellent for finding out small objects resembling fossils. With micro-CT, scientists can take high-resolution 3D pictures and entry the inside construction of fossils with out the necessity to lower them open.
These scans additionally permit for digital copies of the fossils, which different scientists can then entry from anyplace on the earth. This considerably reduces the danger of harm, for the reason that scanned fossils can safely stay in a museum assortment, for instance.
Micro-CT is widespread and routinely used. The scientific group extensively regards it as “non-destructive” as a result of it doesn’t trigger any visible harm – nevertheless it may nonetheless have an effect on the fossil.
Jaw bone of the human fossil species Homo antecessor from Spain. Left: micro-CT scan with a slicing airplane to visualise the inside buildings, bone and enamel; proper: 3D reconstruction primarily based on the high-resolution micro-CT pictures.
Laura Martín-Francés
How does micro-CT imaging work?
Micro-CT scanning makes use of X-rays and laptop software program to supply high-resolution pictures and reconstruct the fossil specimens intimately. Usually, palaeontologists use business scanners for this, however extra superior investigations might use highly effective X-ray beams generated at a synchrotron.
The X-rays undergo the specimen and are captured by a detector on the opposite finish. This enables for a really fine-grained understanding of the matter they’ve handed by way of – particularly density, which then gives clues concerning the form of the interior buildings, the composition of the tissues, or any contamination.
The scan produces a succession of 2D pictures from all angles. Pc software program is then used to “clean up” these high-resolution pictures and assemble them right into a 3D form – a digital copy of the fossil and its inside buildings.
Instance of micro-CT outcomes on a hominin fossil generally known as Little Foot, from southern Africa.
However X-rays should not innocent
X-rays are a sort of ionising radiation. This implies they’ve a excessive degree of power and might break electrons away from atoms (that is known as ionisation).
In residing tissue, ionising radiation can harm cells and DNA, though the extent of harm will rely upon the length and depth of publicity. X-rays and CT scans utilized in medication usually have a really low danger for the reason that publicity of the human physique is diminished as a lot as doable.
Nonetheless, regardless of what we all know concerning the influence of X-rays on residing cells, the potential influence of X-rays on fossils by way of micro-CT imaging has by no means been deeply investigated.
What did our examine discover?
Utilizing normal settings on a typical micro-CT scanner, we scanned a number of trendy and fossil bones and enamel from animals. We additionally measured their collagen content material earlier than and after scanning.
Collagen is helpful for a lot of analytical functions, resembling discovering out the age of the fossils utilizing radiocarbon relationship, or for steady isotope evaluation – a technique used to deduce the food regimen of the extinct species, for instance. The collagen content material in fossils is normally a lot decrease than in trendy specimens as a result of it slowly breaks down over time.
After evaluating our measurements with unscanned samples taken from the identical specimens, we discovered two issues.
This exhibits micro-CT imaging has a non-negligible influence on fossils that comprise collagen traces. Whereas this was to be anticipated, the influence hasn’t been experimentally confirmed earlier than.
It’s doable some fossil samples received’t have sufficient collagen left after micro-CT scanning. This is able to make them unsuitable for a spread of analytical strategies, together with radiocarbon relationship.
What now?
In a earlier examine, we confirmed micro-CT can artificially “age” fossils later dated with a technique known as electron spin resonance. It’s generally used so far fossils older than 50,000 years – past what the radiocarbon methodology can discern.
This earlier examine and our new work present that micro-CT scanning might considerably and irreversibly change the fossil and the knowledge it holds.
Regardless of inflicting no seen harm to the fossil, we argue that on this context the approach ought to now not be considered non-destructive.
Micro-CT imaging is extremely helpful in palaeontology and palaeoanthropology, little doubt about that. However our outcomes recommend it ought to be used sparingly to minimise how a lot fossils are uncovered to X-rays. There are tips scientists can use to minimise harm. Freely sharing knowledge to keep away from repeated scans of the identical specimen might be useful, too.
