In the Dora-Maira massifin Piedmont in the Western Alps, have been found fossils dating back to around 300 millions of years ago within metamorphic rocks coming from the earth’s mantle. Making the discovery, published in a study in the journal Naturewas a team of researchers from the Universities of Turin and Perugia. Fossils, which consist pollen, spores and microscopic marine organismshave been identified on the surface, but the rocks that host them were once found at 100km depth in the Earth’s mantle. These rocks had collapsed due to crustal movements, only to re-emerge with the formation of the Alpine chain. This is an extraordinary find, the first in the world of this kind, because it calls into question the hypothesis that fossils cannot survive the very high temperature and pressure conditions that characterize the mantle. This means that even on other planets, such as Mars, traces of past life could be found at previously unimagined depths.
The discovery of fossils in the Western Alps
The team of researchers, led by Professor Rodolfo Carosi of the Department of Earth Sciences ofUniversity of Turindiscovered the fossils in the Dora-Maira Massif, in the Western Alps, as part of a mapping project. THE fossilswhich include pollen, spores and microscopic marine organisms of the Paleozoic dating back about 300 million yearswere found inside metamorphic rocks emerging on the surface. Fossils are very rare in metamorphic rockssince these are the result of transformations of pre-existing rocks brought to great depths by the movements of the earth’s crust. Here they are very high pressures and temperatures in fact, they cause significant deformations and recrystallization of the minerals. These conditions lead fossils to dissolve or alterso it becomes very difficult to locate them. Those found in the Dora-Maira Massif are found in ten samples rich in graphite very dark that had to be bleached to be able to recognize them.
The importance of the discovery of fossils
The discovery is exceptional due to the tectonic events to which the rocks hosting the fossils have been subjected over time. About 300 million years ago these remains of organisms were found on the surface within sedimentary rocks. During theHercynian orogenyor varisicathe process that contributed to the formation of European mountain ranges between 350 and 250 million years agothese rocks were brought into depth by the movements of the earth’s crust and were transformed into metamorphic rocks. Subsequently, during theAlpine orogenybegun 100 million years agothe rocks were brought back to the surface. During these processes they achieved depth of 100 km in the mantle terrestrial, where the pressure was very high (up to 29 kbar)as well as the temperature (approximately 520 °C). It’s proof that fossils like this can withstand extreme conditionspreserving itself well and contributing to reconstruct the geological evolution of the mountain range. The discovery could also have implications in search for life on other planetswhere traces of it could be found at depths never before hypothesized.
