The calm between extraterrestrial bombardment and free oxygen. Reducing atmosphere supports the development of anaerobic prokaryotes (common ancestors of us and the Archea). Continents smaller than they are today because Earth's thermal heatflow three times higher than today.
Gymnosperms and fern allies are dominant land plants. First flying vertebrates (pterosaurs). Pangaea endures as a single supercontinent. Massive volcanic eruptions (and extinctions) toward beginning of period as Pangaea begins to break up. Great radiation of dinosaurs. India begins to drift from Africa toward Asia, but other continents as now, although in different positions. Dinosaurs dominant. First adaptive radiation of birds. Extensive oceanic transgression. Great angiosperm radiation takes place, although land biomass is probably still dominated by gymnosperms up until the end of this period, the notorious Cretaceous-Tertiary extinction event.
The calm between extraterrestrial bombardment and free oxygen. Reducing atmosphere supports the development of anaerobic prokaryotes (common ancestors of us and the Archea). Continents smaller than they are today because Earth's thermal heatflow three times higher than today.
The Oxygen Catastrophe. Green bacteria (ancestors of chloroplasts as well as of contemporary green bacteria) produce free diatomic oxygen which floods the Earth's atmosphere and oceans. To the existing obligate anaerobes, oxygen is a potent toxin, and they retreat to something like their contemporary habitats. The ancestors of mitochondria and contemporary aerobic bacteria probably arose around this time as well. The Paleoproterozoic era is the first of three eras of the Proterozoic eon.
The Paleozoic era begins, and the Phanerozoic eon with it. The great radiation of animalphyla probably happened during the late Neoproterozoic, but most of the fossil record of it was deposited during this time period.
trilobites, brachiopods, (Taconic orogeny, Gondwana forms?) Ordovician landscapes are purely rock, sand, clay, wind, and water: all macroscopic life is still confined to the ocean.
The Mesozoic era begins.Gymnosperms and fern allies are dominant land plants. First flying vertebrates (pterosaurs). Pangaea endures as a single supercontinent. Massive volcanic eruptions (and extinctions) toward end of period as Pangaea begins to break up.
India still joined to Africa, but other continents as now, although in different positions. Dinosaurs dominant. First adaptive radiation of birds. Extensive oceanic transgression. Great angiosperm radiation takes place, although land biomass is probably still dominated by gymnosperms up until the end of this period, the notorious Cretaceous-Tertiary extinction event.
The Cenozoic era (see below) begins. Great radiation of mammals and further reradiation of birds. Gradual cooling trend, retreat of shallow continental seas. Angiosperms become dominant land plants except in the taiga.
The Tertiary and the Paleogene periods begin, simultaneously. Begins with ecological recovery from the KT extinction event, with attendant radiation of mammals, birds, and angiosperms on land. Ends with a heat wave.
Exceptionally warm and homogeneous climate. Typical of the Paleogene period, in that it comprises the central half of it, the Eocene epoch was the warmest epoch of the Cenozoic. Throughout most of the Eocene, what we now think of as tropical forests grew up to very high latitudes (60 degrees or more) and mammals were generally smaller than in cooler epochs. The Azolla event produced by the warm climate is thought to have sequestered enough carbon to lead to our cooler climate today. Sirenians and cetaceans were developing during this epoch. The Indian subcontinent approached close enough to Eurasia to begin the Himalayan orogeny.
South America separates from Antarctica and drifts north, allowing cool ocean circulation all the way around the continent and the development of the Antarctic ice cap as the epoch opened. The cool spell lasted throughout the entire epoch, the end of which is marked by the melting of the Antarctic ice again. The Paleogene ends at the same time the Oligocene epoch does.
The Neogene period begins, and the Miocene epoch comprises most of it and so may be said to be typical of the Neogene. The Miocene began with the melting of the Oligocene Antarctic icecap, but cooling trends continued, and the Antarctic icecap reformed from the late Miocene onward. Great radiation of grasses and ruminants as grasslands expand over territory formerly covered with forest.
Australopithecines, mostly confined to this epoch, are completely bipedal. Antarctica remains icebound, as the Pliocene is cooler than the Miocene. The Pliocene is only one-fifth as long as the Miocene. The Tertiary period ends at the same time the Pliocene does (see Gelasian).
The Quaternary begins (see Gelasian). The Pleistocene epoch is known in archeology as the Paleolithic and is also known popularly as the Ice Ages. See Eemian interglacial for information about the last time (125,000 years ago) global climate was as warm as it is getting to be now. However, just as the Pliocene was cooler than the Miocene, the Pleistocene was cooler than the Pliocene. The Pleistocene is only half as long as the Pliocene, but encompasses almost all of human evolution since the australopithecine type. This epoch ends with the Younger Dryas. For general information see Timeline of glaciation.
