The Journey of a Fossil

One hundred million years ago, an ammonoid lived in the sea that then separated India from Asia. It died and fell into limy sediments on the seafloor. These sediments grew deeper and hardened into rock. The shell calcified, becoming part of the rock, though maintaining every detail of its structure. India was on the move, drifting on a slab of the Earth's mobile crust toward Asia. The floor of the intervening sea was forced under the Asian continent, back into the hot interior of the planet. ...

 The Evolution of the Breast

About sixty-five million years ago, at the end of the Mesozoic era and the beginning of the Cenozoic, the niche once dominated by the dinosaurs was available for other creatures. The opportunistic could move into that niche now empty of large reptiles, and prosper in their place. Among these creatures that flourished were small egg-laying animals. group that had been around for at least a million years and that sported specialized patches on their chests. Sitting on their eggs, the mothers of...