Friday mystery object #65 answer

On Friday I gave you this bit of geology to identify:

I used this because I had it to hand on Thursday afternoon after doing a behind the scenes tour of the Horniman’s store for some of the attendees of TAM London. I also used it so I would have the chance to tell the story behind this innocuous looking, if pretty, bit of stone.

Before I get started on the story I must congratulate Steven D. Garber, PhD on spotting that one of the main components of this is serpentine (the other being calcite) and I have to hand a big dose of kudos to Dave Godfrey who got the answer spot-on when he suggested that this was a sample of Eozoön canadenese – this one is from Petite-Nation, Quebec.

The reason this piece of rock is of interest is mostly down to the history of its interpretation. We now know that it’s a piece of metamorphosed limestone (= marble) with banding of green serpentine and white calcite. This piece is around 1.1 billion years old, but younger pieces have been found associated with volcanoes – it’s not restricted in occurrence by age, but by the opportunity for formation. What makes it interesting – and explains the reason for it having a name formulated like something biological (“Dawn animal of Canada“) – is that it was interpreted as being a giant Foraminiferan a couple of years after it was found in 1863.

This was big news. It followed the publication of Origin of Species and Darwin’s acknowledgement of a weakness that he perceived in his theory of evolution through Natural Selection – the lack of fossils from Precambrian sediments (about which there is a useful review by Schopf, 2000). In the opinion of eminent geologist John William Dawson this geological structure represented a form of life far more advanced than could be accounted for by Darwin’s theory, in which species originating by gradual adaptation from more simple forms. Darwin acknowledged this discovery in the fourth edition of Origin, but other geologists gave the discovery short shrift and were rapidly reassessing the interpretations of Dawson and preferring a mineralogical explanation for the structures. Unsurprisingly, a heated debate arose.

For most scientists this issue was convincingly and finally resolved in 1894, when blocks of young limestone with the same serpentine structures were found in ejecta from Mount Vesuvius. However, Dawson refused to acknowledge this evidence and held on to his belief in Eozoön being biological (and thus evidence against evolution) until his death in 1899. So what Dawson considered “one of the brightest gems in the scientific crown of the Geological Survey of Canada” turned out to be a petty bauble of no real significance.

5 thoughts on “Friday mystery object #65 answer

    • Thanks for the interesting reference – my knowledge of metamorphism is limited, coming from a palaeontological/sedimentological background, so it’s great to find out more about the processes involved. Cheers!

  1. I was very tempted to answer this one, having been on the tour in question 🙂

    It was a wonderful tour, and provided a fascinating insight into dealing with identifying, storing and preserving stuff (alien concepts in our disposable world) and how all this stuff fits into the bigger picture.

    The next day we looked at the Linnean collection, which is a largely static collection, stored in an underground temperature and humidity controlled vault, in expensive custom made drawers and shelves – all just a bit too clinical 🙂

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