X-rays brighter than a million Sun's show fossil leaf chemistry preserved for 50 million years!

Palaeontologists, geochemists and physicists from the University of Manchester, (UK) Diamond Lightsource (UK) and the Stanford Synchrotron Radiation Lightsource (USA) have published a new paper in the Royal Society of Chemistry journal, Metallomics, that has shed new light, in fact one of the brightest lights in the universe, on 50 million year old fossil plants.

 

Optical plus x-ray false colour composite image (Cu=red, Zn=gren and Ni=blue), image width 17cm. Also visible are characteristic trumpet shaped feeding tubes left by ancient caterpillars: feeding tube chemistry matches the leaves. Data collected at Stanford Synchrotron Radiation Lightsource (SSRL), a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences. Image reproduced courtesy of the Royal Society of Chemistry, Edwards et al 2014, Metallomics, DOI:10.1039/C3MT00242J.

Dr. Nicholas Edwards, a postdoctoral researcher at the University of Manchester and a lead author on the paper said: “The synchrotron has already shown its potential in teasing new information from fossils, in particular our group’s previous work on pigmentation in fossil animals. With this study, we wanted to use the same techniques to see whether we could extract a similar level of biochemical information from a completely different part of the tree of life.”

False colour image of copper (red) and zinc (green) distribution within a modern leaf (A. pseudoplatanus). The distribution of these metals defines the vascular system. Image width ~3 mm. Image from data acquired at the Diamond Light Source, the UK’s national synchrotron science facility.      

Dr. Edwards went on to say “To do that we needed to test the chemistry of the fossil plants, to see whether the fossil material was derived directly from the living organisms or degraded and replaced by the fossilisation process. We know that plant chemistry can be preserved over hundreds of millions of years. Today we even rely on this preserved chemistry as the fossil fuels that power our society.”

However, this is just the “combustible” part, until now no-one has completed this type of study of the other biochemical components of fossil plants, such as metals.

By combining the unique capabilities of two synchrotron facilities, our team were able to produce detailed images of where the various elements of the periodic table were located within both living and fossil leaves as well as being able to show how these elements were combined with other elements.

The work shows that the distributions of copper, zinc and nickel in the fossil leaves were almost identical to those in modern leaves. Each element was concentrated in distinct biological structures such as the veins and the edges of the leaves. Also, the way these trace elements and sulfur were attached to other elements was very similar to that seen in modern leaves and plant matter in soils.

X-ray false colour composite image (Cu = red, Zn = green, and Ni =blue) of a 50 million year old leaf fossil. Trace metals correlate with original biological structures. This leaf was skeletonized by insects which have left behind characteristic trumpet shaped feeding tubes as shown in the inset. Inset: copper only map revealing detail of feeding tube and fine scale veins. Feeding tube chemistry matches the leaves. Image width ~17 cm.  Data collected at Stanford Synchrotron Radiation Lightsource (SSRL), a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences.Image reproduced courtesy of the Royal Society of Chemistry, Edwards et al 2014, Metallomics, DOI:10.1039/C3MT00242J.

Professor Roy Wogelius, also of the University of Manchester and one of the senior authors said: “This type of chemical mapping and the ability to determine the atomic arrangement of biologically important elements such as copper and sulfur can only be accomplished at a synchrotron. In one beautiful specimen, the leaf has been partially eaten by caterpillars and their feeding tubes are preserved on the leaf. We see this behaviour with modern caterpillars. The chemistry of these fossil tubes remarkably still matches that of the leaf on which the caterpillars fed.”

The data from a suite of other techniques performed at the University of Manchester has lead the team to conclude that the chemistry of the fossil leaves is not wholly sourced from the surrounding environment as has previously been suggested but represents that of the living leaves.

Another modern day connection suggests a way in which these specimens are so beautifully preserved over millions of years. We think that copper may have aided preservation by acting as a ‘natural’ biocide, slowing down the usual microbial breakdown that would destroy delicate leaf tissues. This property of copper is utilised today in the same wood preservatives that you paint on your garden fence before an inclement season.

Dr. Uwe Bergmann a co-author on the paper from Stanford, also remarked: “Part of what I do involves detailed measurements of the physics of how plants actually harness light energy using transition metals. Here, we are able to show what metals were present, and where, within extremely old plants- and this just may let us understand, eventually, how the complicated physics of life has developed over long periods of time.”

   Fine scale false colour X-ray map of the Cu distribution within a modern leaf (left) compared to a 50 million year old fossil leaf (right). Primary, secondary, and tertiary venation comparable to the modern leaf can be resolved in the Cu distribution even after 50 million years of ageing. Data acquired at the Diamond Light Source (left panel), the UK’s national synchrotron science facility, and the Stanford Synchrotron Radiation Lightsource (right panel), a national user facility operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences.  Image widths: left ~2.5 mm, right ~10 mm.  Image reproduced courtesy of the Royal Society of Chemistry, Edwards et al 2014, Metallomics, DOI:10.1039/C3MT00242J.

Dr. Bart van Dongen, another University of Manchester geochemist stated: “There is a sharp contrast in the chemistry of the fossils from that of the rock in which they are entombed. This is true for both the trace metals and the organic compounds. The organic part of the chemistry clearly shows a plant derived component.” Dr. Nicholas Edwards added: “This opens up the possibility to study part of the biochemistry of ancient plants, so in the future it may enable us observe the changes, if any, in the use of metals by the plant kingdom through geological time.”

It seems the fidelity that fossil leaves already bring to the palaeontological table has been significantly enhanced by these new findings.

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