The Use of the Electron Microscope in the 

 Study of Fossils 



By William W. Hay 



Department of Geology, University of Illinois 



[With 4 plates] 



The electrox microscope has proved to be a valuable tool in many 

 fields of science. However, only in the past few years has electron- 

 microscopy become a common teclinique for paleontologic research. 

 It is now possible to investigate the skeletal hard-parts of living 

 organisms and fossils in greater detail than was thought possible a few- 

 years ago. Two broad avenues of investigation have opened up : (1) 

 Study of the structural building-blocks and the ultramicroscopic archi- 

 tecture of skeletal materials, and (2) investigation of modern and fos- 

 sil skeletal elements too small to be seen distinctly with the light 

 microscope. 



The hard-parts of organisms are of particular interest to paleon- 

 tologists, those scientists who study fossils, since the most likely re- 

 mains to be preserved in rocks are mineralized skeletal parts. The 

 paleontologist has been able to study the shape and surface features 

 of shells. By cutting sections so thin they transmit light, he has been 

 able to investigate the internal structure of shell materials in the light 

 microscope. 



In any investigation using microscopy, the resolving power of the 

 instrument is an important factor to consider in interpretation of the 

 results. The term "resolving power" refers to the ability of an optical 

 system to produce an image sharp enough to distinguish between two 

 closely spaced points. The resolution of an inexpensive light micro- 

 scope may be as low as 2 p.,^ that is, points less than 2 fx apart cannot be 

 seen as separated points in the final image. The resolving power of 

 an instrument depends in large part on the wavelength of the light or 

 other electromagnetic radiation used to make the observations. It 

 is impossible to resolve two points closer than one-half the wavelength 

 of the light used. The wavelength of light in the visible spectrum is 



1 The micron, usually written ft, is a unit of measure commonly employed in microscopy. 

 1/4 is 1/1,000,000 meter, or 1/1,000 millimeter, or about 1/40,000 inch. 



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