Life, which first inhabited the seas and then moved to land billions of years ago, is an amazing story. Through investigation of ancient trailblazers such as Tiktaalik, a missing link found on Ellesmere Island, we learn the gradual process by which lungs and legs evolved, and how the creatures of the seas eventually conquered the land. Competition for survival forced creatures to adapt.  In the Devonian period when trees appeared and rivers began to flow, fish embarked on a new era in evolutionary history.  The first tetrapods adapted to live a complete life cycle on land and diverged into millions of species of reptiles, birds, amphibians, and mammals.  

Reverse evolution, from land to sea also happened as evidenced by the Basilosaurus whale fossil and Pakicetus, the amphibious wolf-like mammal that eventually took to the sea.  Evolution is not directional, it is opportunistic.  The study of life through time helps us understand where we came from in the history of life on earth.