Credit: © 2007 Elsevier

Fossils have long been considered the domain of sedimentary rocks, but new research demonstrates that they can be preserved during the high pressure and temperature conditions that produce metamorphic rocks.

Sylvain Bernard at the Laboratoire de Geologie, ENS-CNRS in Paris, France and colleagues1 used electron and X-ray microscopy techniques to analyse whole sections of metamorphosed Triassic sedimentary rocks from the French Alps. The rocks, originally formed in lakes, were buried to depths of ∼35 km and heated to ∼360° C during the formation of the Alps. Despite having experienced such harsh conditions, plant material was apparent among the co-occurring metamorphic minerals. Spores from the oldest known group of present-day plants — the lycophytes — were especially prevalent. Organic matter associated with the carbonaceous spore walls was so well preserved that the various compounds could be identified as substances such as fatty acids.

One of the major limiting factors of studying early environments is the scarcity of ancient unaltered sedimentary rocks preserved on the surface of Earth. The techniques presented here demonstrate the potential of looking for clues to the origins of life in a whole new realm of rocks.