Wednesday, 3 April 2013

How Science Works: The Scanning Electron Microscope

Happy Easter! 

It has been a while since my last post, but I will continue posting with news of my research activities.

The sample processing is finished (428 samples done: at last!), microfossil picking and the geochemical analysis of samples continues. So now the pieces of the puzzle are starting to fit together and a picture of the environment in which the tetrapods lived is starting to emerge.

Recently my volunteer Tom and I looked at some of the microfossils we have been picking on the Scanning Electron Microscope (SEM). This is one of my favourite machines to use, as it enables one to see microfossils at great magnification! You can see tiny structures and identify differences in chemical composition, for example shells made from calcite or phosphate. Micropalaeontologists commonly use the SEM and sedimentologists use it to examine thin sections of rocks to look at grain composition and textures. In my research I use it to examine microfossils and sediment thin sections.

The SEM works by firing an electron beam at the surface of a sample, under vacuum conditions. The electrons interact with the surface of the sample, which causes other electrons to be emitted. These are detected and are turned into an image of the sample. We used the machine in Back Scatter Electron mode, which means that the image shows up differences in the chemical composition of the sample.

The Scanning Electron Microscope at the Department of Geology, University of Leicester

The specimens we examined included plant material, ostracods, fish fragments and bone fragments, all from the same rock. Photos of a bone fragment and a fish fragment are shown below. In the fish fragment you can see that the fossil material is white coloured compared to the grey rock background, due to their differences in composition; the fossil is composed of calcium phosphate, the rock of clay minerals.

Top: A bone fragment, length 0.5mm. Bottom: fish fragment, image is 4mm across.

Through identifying different microfossils from rocks in which tetrapods are found we will build up a picture of the different animals living at the time, and the different environments in which the tetrapods lived and died.

Can you get more detailed than a SEM? Yes, you can! If you have fossils with 3D preservation you can digitally image them in 3D using a micro-CT scan. Giles Miller from the Natural History Museum explains how this is done in his fantastic Micropalaeontology Blog  

News Update: Borehole drilling begins on Monday 8th April…. Watch this space for updates!

Until next time


  1. Fascinating to discover what can be seen when you magnify things to such a degree. As a 'macro' person (ie used to dealing with specimens you can see and pick up) it's great to find out how much we can learn when looking at the really fine detail. It's a whole new world as far as I'm concerned. Great stuff, Carys!

  2. Thanks Rob for your comment! The SEM is fantastic... it really does reveal a whole new world!