Some of the oldest known rock formations , formed over 3,700 million years ago , include banded iron layers .
Some of the oldest known rock formations , formed over 3,700 million years ago ( mya ) , include banded iron layers .
Mantell 's work on the structure and life of `` Iguanodon '' began the scientific study of dinosaurs . In 1822 he was responsible for the discovery ( and the eventual identification ) of the first fossil teeth , and later much of the skeleton , of `` Iguanodon '' .