Short answers, pulled from the story.
Georges Cuvier published the paper titled On the species of living and fossil elephants in 1796. This document contained detailed evidence proving that some animals had gone extinct forever rather than simply migrating to unknown lands.
Ivan Yefremov introduced the term taphonomy in 1940 as a new branch of paleontology. The field gained prominence during the 1960s when scientists realized how fossilized deposits relate to original ecosystems.
Current standard recognizes four eons, ten eras, 22 periods, 37 epochs and 96 ages including present day Meghalayan age within Holocene epoch. Geological history was viewed as continuously changing with periods of calm and chaos driven by causes present today and deep past.
Ardipithecus is one of oldest known human branch hominids having lived 4.4 million years ago only found in 1994. Species of genus Australopithecus across Africa named since 1970s are slightly younger but already show bipedal stance of modern humans.
Cretaceous-Paleogene extinction event believed caused by asteroid impact triggering global wildfires disrupting nutrient cycle ocean. This unprecedented rapid extinction occurring over one or few years remains debated with suggestions marine regression volcanism near same time as impact.