During the first two years of the expedition, Darwin collected several fossil mammals from Argentina and Uruguay. It was in the cliffs near Punta Alta, that Darwin recovered his first fossil bones. It was of a large extinct mammal. He sent all the specimens to his mentor, John Stevens Henslow.
A fossil tooth helped Darwin to identify the little-known Megatherium. Megatherium was a genus of elephant-sized ground sloths, endemic to South America. These findings later helped Darwin in formulating the theories about evolution of life.
Darwin was interested in geology too and he studied volcanic rock formations intently. He was surprised to find the fossils of sea creatures at high altitudes, or thousands of metres above sea level. This led to his exploring further into the realities of natural disaster.
During this voyage Darwin was witness to a severe earthquake in Chile on 20th February, 1835 which was claimed to be the largest earthquake ever recorded in Chile. Thus the voyage was eventful as well as significant.