Life transformed into stone
“Come to think of it, if we had a time machine and went back several hundred million years, we might find ourselves thrown from the Dolimites into the bottom of the ancient ocean of Tethys that separated northern Africa from Europe and Asia. Or, if we went back even further, we might find ourselves in the middle of a world dominated by dinosaurs. The long ‘history’ that the Dolomites reveals makes this landscape even more interesting and beautiful...wouldn’t you agree?” (Andrea Irsara)
To understand the above passage, it is important to recall that the Dolomite landscape was named a UNESCO World Heritage Site in 2009 not only for its exceptional natural beauty, but for its earth science values, as well. In fact, aesthetic and landscape values aside, the Dolomites include several important stratigraphic type segments and rock formations that provide evidence of a long geological history and of the evolution of life on earth that can be ascribed to at least 250 million years ago. Life in the Dolomites is actually preserved in stone: this includes fossil records, living beings that, through a process lasting millions of years, have turned into stone.
To understand how the complex formation of mountains and oceans lasts tens and hundreds of millions of years, we must first consider that the earth’s crust is composed of many continental plates that are constantly moving: when the plates move apart, they create new oceans; when they converge, they create mountains.
Two hundred sixty million years ago, the earth’s surface formed a single supercontinent called Pangea that was surrounded by an ocean known as Paleo-Tethys.
During this geological period, the area that later became the Dolomites was covered by an arid desert and was roughly at the level of the equator. Then, the ground in this geographical area slowly dropped and a shallow tropical sea full of life, little by little, submerged the entire region.
About 252 million years ago, at the end of the Permian period, a series of huge volcanic eruptions caused a devastating mass extinction that almost terminated all life on earth. Life in the seas resumed very slowly.
The skeletons of limestone algae and sponges started depositing and accumulating at the bottom of the sea, becoming gigantic reefs like those corresponding to the barrier reefs we have today in the tropical seas. The Sciliar, Odle and Sasso Putia mountains are what remain of these ancient reefs.
The growth of the reefs was interrupted roughly 235 million years ago by new immense volcanic eruptions that created volcanic islands which, together with the reefs, created a landscape similar to the present Seychelles or the Maldives. The Sassolungo, the Sella Massif and the Gardenaccia plateau are remains of this ancient archipelago composed of reefs similar to atolls. The invertebrate fauna remains from the San Cassiano Formation that includes excellently preserved fossil shells and is one of the best known in the world for its extremely diverse species and form, dates back to this period.
The “dolimite” islands, on the other hand, enjoyed tropical climates and were populated by many land and sea reptiles. Isolated remains of these reptiles such as the pelvis, the spine and a femur of a Nothosaurus have been found in the San Cassiano Formation.
Over the course of millions of years, the shallow sea basins filled with debris, creating a broad partly coastal and partly lagoon flat expanse hospitable to many dinosaurs. This is when the sequence of the Dolomia Principale Formation that includes the Tre Cime di Lavaredo and the bases of the Sasso della Croce, Conturines and Lavarella started.
Halfway through the Jurassic period – about 175 million years ago – the entire dolomite area that was composed of sedimentary and volcanic rock collapsed hundreds of meters to form the bottom of a deep ocean. Sediments accumulated on the sea floor, as well as the Rosso Ammonitico – a reddish rock that gets its name from the numerous ammonites it contains. Hence, the rocky mountains that today offer us a spectacular sight beyond comparison were once lying at the bottom of the Tethys Ocean. This is when the rock formation cycle ends and orogenesis – the primary mechanism by which mountain ranges are built – begins. The Dolomites began “emerging” from the richly stratified sea floor during the Cretaceous – roughly 100 million years ago – due to a collision between the African and European continents. The folds and uplift caused by the convergent movements between the two plates created the Alps and the formation of the Dolomites. This uplift still continues today.