The Geologic Time Scale is simply a list of the ages of the Earth and its past life forms. We call these representations of former animal and plant life, FOSSILS, the study of which is termed Palaeontology. Fossils may be petrified tree trunks, roots, bones, teeth, feathers, impressions or casts of a plant or animal, the plants and animals preserved in amber (the sticky resin of fossil plants or trees such as the pine),etc. Or they can be what are called Trace Fossils (Ichnology), such as tracks, trails, excrement, and burrows, among others. In some cases mummified and/or frozen organisms are discovered, including the actual skin , hair and other "soft" tissues. The origin of the sometimes weird sounding names used in the following list is, in itself, a historical journey into the original places in the world where the classical fossil collecting localities are located, or the names of ancient tribes who inhabited the regions, as well as Greek words whose roots designate the forms of life from the most ancient to the youngest. An online encyclopaedia would be useful in researching this historical background. The names appearing here of the various divisions of the past history of this planet are only the most basic ones, largely those of American usage. In Europe they assign different names in some cases. There are many more divisions and subdivisions, based mainly on localized geographical, geological and/or palaeontological considerations. The age in years before the present (M = millions of years) is constantly changing as more precise scientific dating methods are discovered and are only presented here as a guide. The same may be said of the forms of life present. Every year new fossils are discovered which extend back even farther into the past the lineage of certain organisms.

The Geologic Time Scale

Era	Period	Epoch	Age (yrs)	Life Forms
Cenozoic	Quaternary	Holocene	10.000	modern life forms
		Pleistocene	2 Million	LAST ICE AGE, large terrestrial mammals, mammoths, mastodons, first modern man, cave paintings
	Tertiary	Pliocene	7 M	first Australopithecines, toolmaking, Neanderthals
		Miocene	25 M	large sharks, whales, first hominids
		Oligocene	40 M	first grasses, anthropoids
		Eocene	55 M	first marine & large terrestrial mammals
		Paleocene	64 M	many kinds of mammals
Mesozoic	Cretaceous		137 M	AGE OF DINOSAURS, mollusks, dinosaurs, first primates, flowering plants,
	Jurassic		195 M	first belemnites, squids, frogs, birds, salamanders
	Triassic		225 M	first turtles, cycads, lizards, dinosaurs, mammals
Paleozoic	Permian		280 M	first mammal-like reptiles
	Carboniferous	Pennsylvanian	325 M	COAL AGE, first conifers
		Mississippian	345 M	first reptiles, spiders
	Devonian		395 M	AGE OF FISH, first insects, ammonites, jawless fish, placoderms, amphibians
	Silurian		440 M	first land plants, ferns, lycopods, sharks, boney fish
	Ordovician		500 M	first corals, starfish, sea urchins, blastoids, eurypterids, bryozoa, scaphopods, vertebrates
	Cambrian		570 M	first trilobites, conodonts, forams, sponges, worms, brachiopods, nautiloids, chitons, clams, snails, monoplacophorans, crustacea, crinoids, cystoids, carpoids
Archaeozoic	Precambrian		>570 M	first simple plants and invertebrate animals: algae, bacteria, jellyfish

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