The Beagle followed a 1,200 mile long area of the South American coast, from the Rio de la Plata to Tierra del Fuego, and Darwin noticed that some rocks in the south were much higher above sea level than the same rocks in the north, as if the whole continent had tilted. As the Beagle went around Cape Horn and was entering the port of Concepción, Chile, on February 20, 1835, a huge earthquake occurred. Looking at the amazing damage, Darwin noticed that rocks near the harbor had been lifted two or three feet, and that shellfish, seaweeds, and other marine organisms were high and dry. Darwin thought that maybe such huge changes in an organism's environment were connected to or caused changes in the organisms and in life on earth.