Short answers, pulled from the story.
The Cenozoic Era began 66 million years ago with the Cretaceous-Paleogene extinction event, triggered by the impact of the Chicxulub impactor. This event ended the reign of the non-avian dinosaurs and opened the era we are still living in.
The name Cenozoic was proposed in 1840 by British geologist John Phillips, who originally spelled it Kainozoic. It derives from the Ancient Greek words kainós, meaning 'new', and zoe, meaning 'life'.
The Cenozoic is called the Age of Mammals because terrestrial life in both hemispheres came to be dominated by mammals after the extinction of the non-avian dinosaurs. Eutherians, or placental mammals, dominated the Northern Hemisphere, while metatherians, or marsupials, dominated the Southern Hemisphere.
The Cenozoic is divided into three periods: the Paleogene, Neogene, and Quaternary. These in turn contain seven epochs: the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene.
The primary driver of Cenozoic cooling was the collision of India with Eurasia, which raised the Himalayas. As the upraised rocks eroded, they reacted with atmospheric gases and reduced the proportion of carbon dioxide in the atmosphere over millions of years. The formation of the Antarctic Circumpolar Current in the Mid-Eocene also contributed by disrupting global ocean circulation.
The Sixth Extinction refers to the ongoing mass extinction attributed to human activity, which began roughly 10,000 years ago. Over 322 species have been formally recorded as extinct due to human activity since the Industrial Revolution, though the true rate may include as many as 500 vertebrate species, with the majority of losses occurring after 1900.