Geologically, the Serra do Mar belongs to the massive crystalline rock platform that forms Eastern South America and tectonically is very stable. Most of the elevations of Serra do Mar were formed about 60 million years ago.
At the time of discovery of Brazil (1500), Serra do Mar supported a rich and highly diversified ecosystem, composed mainly by a lush tropical rain forest, called Mata Atlântica (Atlantic Rainforest). Due to urbanization and deforestation, however, most of the forest cover was destroyed and it remains almost exclusively in the steep escarpments facing the sea. A chain of national and state parks, ecological stations and biological reservations now protect the Mata Atlântica and its biological heritage, but acid rain, pollution, poachers, clandestine loggers, forest fires and encroachment by urban areas and farms are still promoting active destruction, particularly around cities. The largest metropolis of São Paulo, Rio de Janeiro, Curitiba and Vitória are near the Serra do Mar.
Reforestation and recuperation of biological diversity are notoriously difficult to bring about in destroyed rain forest habitats, but Rio de Janeiro boasts of such success in the Mata Atlântica in its city parks.