Dating

Whatever your primary association to the heading of this post may be, the main characters in this story are elephants’ teeth and stars. Inspired by Jon Kalb’s book Adventures in the Bone Trade, I will discuss two aspects of the question: how old is this place or thing?

One of the fundamental methods for dating layers of rock is radiocarbon dating. However, out in the field, if you need a first impression of how old a site of interest may be, radiocarbon dating may come a bit unhandy.

Another approach is given by biostratigraphy which uses fossils for dating. The basic ingredient for this methods is the knowledge which species lived through which geological time span.

Kalb explains in his book, how fossilised teeth of different subspecies of Elephas recki, an extinct elephant species, can be used in this vein. The following figure from Nancy E. Todd’s paper African Elephas recki: Time, space and taxonomy shows the age of the earliest and latest fossils found for different subspecies of Elephas recki.

recki_time

image source: Todd, N. E. (2001). African Elephas recki: Time, space and taxonomy. In: Cavarretta, G., Gioia, P., Mussi, M. and M. R. Palombo. The World of Elephants, Proceedings of the 1st International Congress. Consiglio Nazionale delle Ricerche, Rome, pp. 693–697.

Now, with this knowledge at hand, all that is needed is the ability to identify the Elephas recki subspecies from a given fossil. This is wonderfully supported by the different shapes of molars found in different subspecies (see the figure at the beginning of the post). So, if you are searching for fossils of a given age in a region where Elephas recki was sufficiently abundant, all you need is a few fossilised teeth to get an idea whether searching a certain place is worth your effort.

Questions of this kind abound in science. To give another particularly interesting example let us switch to the following question: how old is that star? For a single star, like for an archeological artefact without a context, this is virtually impossible to answer. If, however, a star is part of a suitable context, in particular of a star cluster, there is a tool at hand, the Elephas recki tooth of astronomy, known as the Hertzsprung-Russel diagram.

This diagram is a scatter plot of the spectral class of stars (think colour) and their luminosity (think brightness). During their evolution, stars are represented in different places in the diagram. Most stars start their lives on the so-called main sequence and then branch off to positions among the giants or subgiants as they inflate towards the end of their lives. Now, stars in a cluster share their birth date and an analysis of how many stars have already branched off from the main sequence allows to estimate the age of a cluster.

To conclude, I suggest to go out and ask How old is that? of as many things as possible and find out about the fascinating ways in which things can be dated. Also, this may give you a lot to talk about when you go for dating.

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