Fossils in Geologic Time

	The Quanternary Period- the present to 1.8 million years ago (MYA) and divided into two Epochs; the Holocene (present - 11,000 years ago) and the Pleistocene (11,000 years ago-1.8 MYA). Since it is believed that humans first appeared during the Holocene Epoch, the Quanternary Period is commonly referred to as the "Age of Man."
	The Tertiary Period - 1.8 to 65 MYA; the longest of the Cenozoic periods.
	The Cretaceous Period- 65-146 MYA; although new dinosaurs appeared during this time, known as the last of the "Age of Dinosaurs"; first primates, angiosperms appear; breaking apart of the world-continent Pangaea begins.
	The Jurassic Period- 146-208 MYA; great plant-eating dinosaurs; lush growths of ferns and palm-like cycads; smaller but vicious carnivores stalking the great herbivores; oceans full of fish, squid, and coiled ammonites; first frogs, salamanders, crocodiles, flying reptiles, birds; oilfields of the North Sea are Jurassic in age.
	The Triassic Period- 208-245 MYA; Pangaea in existence altering global climate and ocean circulation; the appearance of modern conifers, cycadeoids; first turtles, lizards, mammals, dinosaurs.
	The Paleozoic Era- 245-544 MYA; two of the most important events in the history of animal life occurred during this period: (1) at the beginning of the period a dramatic "explosion" of diversity in animal life occurred and (2) near the end of the period, the largest mass extinction in history wiped out approximately 90% of all marine animal species; six major continental land masses existed.
	The Pennsylvanian Period- 286-325 MYA; first conifers, insects, reptiles.
	The Mississippian Period- 325-360 MYA; first seed ferns; belemnoids
	The Proterozoic Era- 544 MYA to 2.5 BYA (billion years ago); stable continents appeared; first abundant fossils of living organisms (primarily bacteria and archaeans) are found in layers of rocks from this Era; first evidence of oxygen build-up in the atmosphere appeared causing an enormous global catastrophe that doomed many existing bacterial groups; first sponges, jellyfish.
	The Archaean Era- 2.5 to 3.8 BYA; true beginning of geological history of the Earth; the atmosphere was likely composed of methane, ammonia, and other toxic gases; the Earth's crust began cooling and rocks and continental plates began to form; the oldest known fossils come from South Africa and Western Australia and date to roughly 3.5 BYA. They consist of bacteria microfossils which were probably the Earth's only inhabitants for more than a billion years of this Era.
	The Hadean Era- Hadean time is not a geological period as such. During the first 800 million or so years of its history, the Earth would likely have been molten and was constantly being bombarded by meteorites and asteroids. With the exception of meteorites that probably struck the Earth as it was being formed, no rocks on the Earth are this old. Some igneous rocks have been Radiometrically dated from the time of solidification of the Earth. This explains why the oldest meteorites and lunar rocks are about 4.5 billion years old, but the oldest Earth rocks currently known are 3.8 billion years old. Once the formation of the Earth was complete, solid rock formed, and geological history began.