If several fossils of an extinct population or species are dated, we can estimate how long ago the extinction event took place. In our new paper, we describe CRIWM, a new method to estimate extinction time using times series of fossils whose ages have been measured by radiocarbon dating. And yes, there’s an R package — Rextinct — to go with that!
While the Earth seems to gather all the conditions for life to thrive, over 99.9% of all species that ever lived are extinct today. From a distance, pristine landscapes might look similar today and millennia ago: blue seas with rocky and sandy coasts and grasslands and mountain ranges watered by rivers and lakes and covered in grass, bush and trees.
But zooming in, the picture is quite different because species identities have never stopped changing — with ‘old’ species being slowly replaced by ‘new’ ones. Fortunately, much like the collection of books in the library summarises the history of literature, the fossilised remnants of extinct organisms represent an archive of the kinds of creatures that have ever lived. This fossil record can be used to determine when and why species disappear. In that context, measuring the age of fossils is a useful task for studying the history of biodiversity and its connections to the planet’s present.
In our new paper published in the journal Quaternary Geochronology (1), we describe CRIWM (calibration-resampled inverse-weighted McInerny), a statistical method to estimate extinction time using times series of fossils that have been dated using radiocarbon dating.
Why radiocarbon dating? Easy. It is the most accurate and precise chronometric method to date fossils younger than 50,000 to 55,000 years old (2, 3). This period covers the Holocene (last 11,700 years or so), and the last stretch of the late Pleistocene (~ 130,000 years ago to the Holocene), a crucial window of time witnessing the demise of Quaternary megafauna at a planetary scale (4) (see videos here, here and here), and the global spread of anatomically modern humans (us) ‘out of Africa’ (see here and here).
Why do we need a statistical method? Fossilisation (the process of body remains being preserved in the rock record) is rare and finding a fossil is so improbable that we need maths to control for the incompleteness of the fossil record and how this fossil record relates to the period of survival of an extinct species.
A brief introduction to radiocarbon dating
First, let’s revise the basics of radiocarbon dating (also explained here and here). This chronometric technique measures the age of carbon-rich organic materials — from shells and bones to the plant and animal components used to write an ancient Koran, make a wine vintage and paint La Mona Lisa and Neanderthal caves.
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