Cretaceous PeriodCharacteristics The Cretaceous Period was the last and longest segment of the Mesozoic Era. It lasted approximately 79 million years, from the minor extinction event that closed the Jurassic Period about 145.5 million years ago to the Cretaceous-Paleogene (K-Pg) extinction event dated at 65.5 million years ago.Types of LifeThe Cretaceous Period was known for its development in flowering plants. As diverse flower forms lured insects to pollinate them, insects adapted to differing ways of gathering nectar and moving pollen thus setting up the intricate co-evolutionary systems we are familiar with today. During the Cretaceous Period, birds replaced the Pterosaurs in the air. Avians were highly successful and became widely diversified during the Cretaceous. Confuciusornis (125 to 140 million years) was a crow-sized bird with a modern beak, but enormous claws at the tips of the wings. Iberomesornis, a contemporary, only the size of a sparrow, was capable of flight and was probably an insectivore. By the end of the Jurassic, the giant Sauropods, such as Apatosaurus, were becoming extinct. Evidence suggests that by the early Cretaceous they were being replaced by large herds of herbivorous Ornithischians such as Stegosaurus, Iguanodon and the Ceratopsians. Theropods, including Tyrannosaurus rex, continued as apex predators until the end of the Cretaceous.ClimateAll over North America, the highest Cretaceous fossils are found directly beneath a thin layer of sediments that contain an unusual amount of iridium, an element otherwise uncommon in Earth’s crust. Also within this layer are indications of “shocked quartz” and tiny glass-like globes called tektites that form when rock is suddenly vaporized then immediately cooled, as happens when an extraterrestrial object strikes the Earth with great force. These remains are found as far north as Colorado. Temperatures would have reached levels high enough to cause flash fires in many locations and a tsunami inundated much of the Eastern United States.It is hypothesized that debris aerosols from the asteroid impact and the resulting fires may have combined with the ash and smoke from the continuing volcanic activity to significantly reduce global temperatures for a few decades. As a result of suddenly lowered temperatures there may have been a global disruption in the numbers of both land plants and plankton in the oceans, evidence of which is part of the K-Pg fossil record. With such a crisis in the photosynthetic communities a cascading crisis would have toppled the food/energy pyramids extant at the time. This hypothesis accounts for the extinction of the largest animals of the time, the dinosaurs and giant marine reptiles. It also explains how smaller animals such as the mammals and other animals with more modest energy requirements managed to survive and diversify in the new Cenozoic Era.
The Pleistocene Epoch (2,588,000-11,700 years ago)One of very bipolar climates indeed. It was this very Epoch that we know as the common Ice Age and brought scientists closer to... well us.The climate in this was characterized as a continuous El Nino. While 30% of the Earth was covered with an icy layer. Places that we know of as warm were covered with glaciers such as New Zealand and Tasmania.The other percentage was considerably warmer. Not as warm as we prefer, but warm enough for the mega flora and fauna that lived in this Epoch to live in. A lot of the species that lived during the Pleisotcene Epoch were larger versions of what we have on Earth today. For example, Mammoths and Ground Sloths were alive at this time. These two are larger versions of species that we have today, the reason for that is that this Epoch was also a marker for Evolution. We start to see a lot of the flora and fauna that are still on our planet today. Roughly 70% of molluscan fauna are still living today too.
MioceneWhen the Miocene is closer to the present day than most other periods of geologic time. It occurred 23.03 to 5.3 million years ago, following the Oligocene epoch, and preceding the Pliocene epoch whereduring the miocene earth look similar to what it looks now. (looking for more info)Geographic Landscaping miocene is well known for expansion of deserts,tundra and grasslands. Mountain ranges began forming in North America. also kelp forest made their first appearance.Climate Climates remained moderately warm, although the slow global cooling that eventually led to the pleistocene glaciations continue.Australia experienced an increase in climate due to its movement north. Life Forms many animal species evolved into fast-running herbivores, large predatory mammals and birds, or small quick birds. apes arose and diversified. By the end of the Miocene, 95% of all modern seed plant families existed. No plant species since the middle of the Miocene have gone extinct. Kelp forest began to appear, along with the retreat of tropical forests. kelp forest made their first appearance and soon became one of Earth's most productive ecosystems