What 415 million year old fossil plankton tells us about heavy metal pollution and extinction

These weird looking things are plankton – from the genus Ancyrochitina to be a little more precise.  They are also fossils – approximately 415 million old, from a period known as the late Silurian.  That’s pretty cool in itself (at least I think so), but what makes this really interesting is that the individual on the left is malformed, whilst the one on the right is ‘normal’.  What is even more interesting than that, is that these malformations coincide with the initial stages of extinction events.

Led by Thijs Vandenbroucke (researcher at the French CNRS and invited professor at Universiteit Gent | Ghent University) and Poul Emsbo (US Geological Survey), an international team of researchers have taken a look at these malformed (known as ‘teratological’) fossil plankton.  They wanted to find out what was causing these malformations.

Looking to modern times to unlock the past
These sorts of malformations aren’t unheard of today.  There is a wealth of science suggesting that heavy metals can cause such malformations in a wide variety of different species, from diatoms and foraminifera, to arthropods and fish.  Using a range of different sampling and analysis techniques, the team checked the plankton fossils for heavy metal contamination to see if this was the likely cause for the malformed plankton.

There is nothing new under the sun
Sure enough the researchers found high levels of heavy metal concentration – like iron, lead, and arsenic, inside the malformed plankton fossils.  We have our primary suspect for malformations, but what does this have to do with extinction events?  The researchers point to other work which looks at the chemical behaviour of heavy metals. They suspect that the increasing levels of heavy metals in the plankton likely arises from reduction in oxygen in the oceans – anoxia.  Despite living in the sea, most marine organisms do need oxygen to survive so it could very well be that anoxia was the cause of a number of mass extinction events that occurring during the Ordovician and Silurian periods (around 485 to 420 million years ago)

The original paper
The paper was published in the journal Nature Communications.  The authors have paid for the paper to be open access, so why not have a read of it yourself http://dx.doi.org/10.1038/ncomms8966

Image: A malformed (’teratological’) chitinozoan specimen of the genus Ancyrochitina (a) and a morphologically normal specimen (b) of the same genus. Both of these Silurian microfossils are from the A1-61 well in Libya and are about 415 Ma old. Scale bars are 0.1 mm.  Image and caption taken from the paper.

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