Daily Archives: April 26, 2014

April 26: A study of the metallic compound distribution within a 50 million year old fossilized leaf

Edwards et al., Leaf metallome preserved over 50 million years. Metallomics, 2014; 6 (4): p. 774-82.

In the past studying fossils simply carefully excavating bones and assembling them into the sorts of exhibits you seen in natural history museums. Recently, however, fossils have become even more interesting as we have developed technologies that can study them to get information that was always there but never previously accessible. Carbon dating was the first example of determining more information from a fossilized sample than was visible to the eye. Recently, scientists have been able to extract DNA from recovered wooly mammoths and Neanderthals.

In this study Edwards et al used a combination of x-ray spectroscopy and a technique called “large-scale synchrotron rapid scanning x-ray fluorescence elemental mapping” (SRS-XRF) to look at a fossilized leaf from the Green River Formation in the Rocky Mountains which has been dated to be 50 million years old. Previous studies had shown that the latter could be used to measure trace metals and sulfur compounds that accumulated in the fossil during its lifetime – giving insight into the biosynthetic properties that the animals used to survive. However, no one had applied this method to fossilized leaves before.

Evidence that the SRS-XRF mapping was genuine comes from the fact that different organometallic and organosulfur compounds were not spread evenly throughout the leaves, but rather were associated with discrete areas, outlining biological structures associated with different processes. Importantly, the compounds detected within the various areas of the leaf were also not in the embedding material – indicating that the mapping wasn’t simply picking up contamination from the soil the fossil had been sitting in for millions of years but actually belonged to the fossil itself. Interestingly, Townsend et al. also used the SRS-XRF method to observe compounds in live leaf material, which can be directly compared and contrasted with the fossilized leaves from history. This method is very exciting and allows for new information to be gleaned about fossilized plants throughout millennia.