WHAT is a fossil made of? Mineralised rocky fossils are what first spring to mind, but others, like the fossils of the Burgess Shale in Canada, are made of pure carbon and can be thought of as proto-coal. There are also tantalising Cretaceous insects preserved in amber.
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Whatever they are made of, fossils contain treasures. The first really good microscopic study of mineralised dinosaur bone was able to reveal its internal structure, and was written up in 1850 by British palaeontologist Gideon Mantell.
Still, classifying fossil organisms on the basis of their structure and location seemed to be virtually the only weapon in the palaeobiologist鈥檚 arsenal until 1993. That was the year the field erupted, as ancient pigments, proteins and DNA were detected (not too reliably at first) in rock and all manner of other fossil substrates: a foundational moment that was captured more or less as it happened by Michael Crichton鈥檚 novel Jurassic Park.
Crichton鈥檚 blood-sucking insects fossilised in amber were a bust in real life. But the author of Remnants of Ancient Life: The new science of old fossils 鈥� a dull title for this vivid, gripping book 鈥� has since extracted traces of ancient haemoglobin from the stomach of a fossilised mosquito, so never say die.
Dale Greenwalt, who spends 11 months of the year 鈥渂uried deep in the bowels鈥� of the Smithsonian鈥檚 National Museum of Natural History in Washington DC, has written a riveting account of a field achieving revolutionary insights. The finds he cites are extraordinary enough: a cholesterol-like molecule found in a 380-million-year-old crustacean and the discovery of the biopolymer chitin in the exoskeleton of a fossil from the 505-million-year-old Burgess Shale, to name just two.
More interesting are the inferences we can draw about the physiology, behaviour and evolution of the organisms these molecules came from. Valuable insights can even come from traces that are fragmented, degraded and condensed, says Greenwalt. It is even possible to calculate and construct hypothetical 鈥渁ncestral proteins鈥� and, from their study, argue strongly that life on Earth originated in deep ocean vents.
The story of biomolecules in palaeontology has its salutary side. Brilliant innovators have had to learn the limitations of their new techniques and return, as often as not, to the insights of comparative anatomy to confirm and calibrate their work. The polymerase chain reaction (PCR) technique is the engine powering our access to ancient DNA sequences, but it had teething problems, including the publication of a DNA sequence thought to be from a 120-million-year-old weevil that actually belonged to a modern fungus.
More problematic are the cul-de-sacs. For instance, plant proteins only last for about 30,000 years, so the revolution currently shaking up palaeobiology seems to have left the botanists high and dry.
Greenwalt sets many wonders against these setbacks, though. And there is a further twist in his tale: it may become possible to classify plants and microbes based on the repertoire of small biomolecules they leave behind.
鈥淭he biomolecular components of plants have been found as biomarkers in rocks that are two and a half billion 鈥� with a 鈥榖鈥�! 鈥� years old,鈥� says Greenwalt. Given that the 3.7-billion-year-old cyanobacteria that produced the stromatolites (layered mounds of sediment made by microorganisms) in Greenland are the same age as the rocks of Mars鈥檚 Gale crater, 鈥淎re authentic ancient biomolecules on Mars so implausible?鈥� asks Greenwalt.
His day job may keep him in the Smithsonian鈥檚 basement, but this researcher鈥檚 gaze is set firmly on the stars.
Simon Ings is a writer based in London
