The Earth is the stage upon which life and living beings are the actors in the work of nature. Some rocks contain imprints of primitive life, in the form of fossils. Fossilisation is a process that requires a very long time and specific conditions. One of the most unique examples of this is amber, the fossilised resin of extinct plants that existed millions of years ago. Some of those plants left traces of wood and leaves as proof of their time in the Earth's ecosystems, as well as amber, an enigmatic treasure whose secrets are gradually starting to be unveiled.
Since July 2008, following the discovery of the Palaeontological Site of Rábago/El Soplao, four excavations have been made and have yielded a vast number of data. The investigation work continues at a good pace and several articles have already been published in scientific journals describing the geology of the site, the botanical affinities and the geochemistry of amber. In addition, new species of insects fossilised in amber have been described.
The first is called Cantabroraphidia marcanoi, alluding to its Cantabrian origin and the insect order to which it belongs, Raphidioptera, and was dedicated to the Cantabrian Governance Councillor, Francisco Javier López Marcano, who made it possible for the research into the amber of the Palaeontological Site and the whole geological area of El Soplao cave to be carried out. The second published species is a specimen belonging to the Thysanoptera order which has been named Tethysthrips hispanicus. These new entries in the catalogue of life are the first in the list of species discovered at the Palaeontological Site of Rábago/El Soplao, which promises to be very long.
The investigation work at the Palaeontological Site of Rábago/El Soplao is being carried out by a team of scientists formed by specialists from the Spanish Geo-Mining Institute, Barcelona University, Lyon University, the Basque Country University, the National Scientific Research Centre (CSIC) and the Astrobiology Centre (INTA-CSIC), among others.
Stromatolites are laminated rocks created by the action of microbes, usually cyanobacteria (also known as cyanophyceae algae). These micro-organisms induce the crystallisation of calcium carbonate when performing photosynthesis and also trap particles carried by water, producing the formation of thin layers of carbonate which act as cement. Currently, most stromatolites are formed in lakes and on sea beds. The oldest known stromatolite fossils are about 3,500 million years old and are the first proof of life on Earth.
Recently, a type of stromatolite not known to date was discovered in El Soplao cave (Cantabria). But, since caves have no light, how is it possible for microbes to perform photosynthesis, which is necessary to build the stromatolithic structure? The answer to this and other questions was recently published in the prestigious scientific journal Geology (Rossi et al., 2010*). This finding is the result of research carried out in El Soplao cave by members of the Spanish Geological and Mining Institute (IGME), the Complutense University of Madrid and Melbourne University (Australia). The research work was conducted as part of an agreement to study the cave signed by the IGME, the Department of Culture, Tourism and Sport of the Regional Government of Cantabria and the company SIEC.
The immaculate whiteness of the helictites of El Soplao strongly contrasts with the black of the recently-discovered stromatolites. This is due the fact that these stromatolites are mainly formed by black manganese oxide and not by calcium carbonate, as usual. Perhaps their black colour in a dark place like the cave explains why the stromatolites have remained unnoticed until now.
The stromatolites of El Soplao were formed more than a million years ago in an old underground river. The manganese dissolved in the river water was used by a special type of microbe that specialises in oxidising manganese. These bacteria are micro-organisms known as "extremophiles", which have adapted to survive in extremely hostile conditions, in this case, a total absence of light and a lack of nutrients. They are "chemosynthetic " organisms, since they use a chemical reaction (oxidising of manganese) to synthesise their organic matter instead of using light, as photosynthetic organisms usually do.
The stromatolites of the Cave contain many traces of micro-organisms, which are in many cases perfectly conserved. This exceptional preservation is due to the sub-product obtained from the chemical reaction which gives rise to the organisms, i.e., the manganese minerals formed outside the cell wall of each of the bacteria. If the biological activity is intense, the bacteria remain surrounded by life among the abundant particles of manganese oxide, with many details of their cell wall being preserved.
The discovery of the manganese stromatolites in El Soplao is a breakthrough in terms of knowledge about extremophile microbes specialising in oxidising manganese. Furthermore, it provides clues to understanding the conditions for the formation of the extremely primitive stromatolites which gave rise to the precipitation of iron and manganese preserved in rocks from the Proterozoic eon, with an age of around 2,000 million years. With this finding, a new line of research is possible in a stromatolites site which is the only one of its kind in the world: El Soplao cave.