It has been said that the modem world unfolded during the Cenozoic Era. It is true that every feature of the modem landscape was formed during the Cenozoic Era. The Alps and the Himalaya have literally risen from the ocean floor. The Rocky mountains have been formed, worn away and re-uplifted to their present heights. The Appalachian Mountains that had formed at the close of the Paleozoic and worn away by the end of the Triassic, were uplifted and sculpted into their present form during the Cenozoic. All the other mountains of the world were also elevated and sculpted to their present form during the past 65 million years. In addition to being a time of landscape sculpting, the Cenozoic Era was also a period of crustal unrest. Some of the mountain building events of the Cenozoic are still underway as is evident from the presence of volcanic activity and earthquakes in many parts of the world. The Cenozoic was also a time when the modem animal and plant world evolved. Life on Earth changed during the Cenozoic in many ways. Many of the animals that had dominated the seas from the marine reptiles to the ammonites had disappeared with their ecological niches being taken over by the modem inhabitants of the sea including bottom-dwelling molluscs, whales, and the teleost fish. On land, the flowering plants became the dominate plants while the mammals took over the spaces once occupied by the dinosaurs.
Renton, John J. and Repine, Thomas, "The Cenozoic Era" (2016). Readings and Notes. 22.