From Tropical Sea to Alpine Peaks
Around 250 million years ago, during the Triassic Period, the region now occupied by the Dolomites was a shallow, warm tropical sea called the Tethys Ocean. In this sunlit water, vast carbonate platforms began to grow, forming structures similar to modern atolls in the Bahamas. These were not built by modern corals. Instead, the primary architects were calcareous algae, sponges, microbial mats, and early species of scleractinian corals. Over millions of years, the accumulation of their calcium carbonate skeletons and other marine sediments built up massive platforms, some rising up to 1,500 meters from the surrounding sea floor.
The rock that forms these mountains is primarily dolomite, a calcium magnesium carbonate mineral, CaMg(CO3)2. This mineral gives the peaks their characteristic pale, ghostly color. The process of dolomitization, where magnesium-rich water alters the original limestone, likely occurred soon after deposition in the hypersaline, evaporative conditions of the Triassic sea. The dramatic vertical walls and towers seen today, such as in the Sella Group and the Sciliar/Schlern formation, are the direct remnants of these ancient platform margins and reef fronts. Volcanic eruptions periodically interrupted this process, depositing darker layers of rock that contrast with the pale carbonate, a feature still visible today.
The African Collision
The serene tropical environment of the Dolomites began to change as the supercontinent of Pangea broke apart. The decisive event in the formation of the modern Alps was the Alpine Orogeny, which began roughly 65 million years ago. The African tectonic plate, moving northward, started to collide with the Eurasian plate. This immense geological collision folded and compressed the Earth's crust, forcing the ancient Tethys seafloor and its thick layers of fossilized carbonate platforms upward.
This process lifted the rock more than 3,000 meters, creating the mountain range. The highest peak in the Dolomites, Marmolada, now stands at 3,343 meters. What was once a horizontal seabed became a vertical landscape of stone. During the ice ages, massive glaciers carved through the uplifted rock, sculpting the sharp peaks and deep valleys that define the region. Some cliffs rise more than 1,500 meters vertically, among the highest limestone walls in the world. Today, hikers can walk through layers of rock containing abundant fossils of Triassic marine life, including ammonites, large bivalves like Megalodon, and shells of the species Daonella, proof of the mountains' oceanic origins.