About 500 million years ago, trilobites such as this were common that once covered much of indiana. violent storms often occurred in the same area and the trilobites were covered quickly by sediment, hidden for hundreds of millions of years.
a) along riverbanks
b) in the sandy plains
c) in warm, shallow seas
d) throughout the mountains

About 500 million years ago, many multicellular organisms lived in the seas. It was a rich life in shallow, warm, and continental seas. The climate was favorable. Reef-forming corals, as well as the first true vertebrates, some fish, appeared. Trilobites were diverse and rich. The name trilobite means three lobes in which their body is divided. They lived in warm shallow seas. They avoided a great extinction of species in that time before they were covered by sediment.

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".