Tertiary

The Tertiary period is one of the major divisions of the geologic timescale, from the end of the Cretaceous period about 64 million years ago to the start of the Quaternary period about 1.6 million years ago. The Tertiary includes five geologic epochs -- the Paleocene, Eocene, Oligocene, Miocene and Pliocene. The Tertiary is sometimes divided into two sub-periods called the Paleogene and Neogene.

It covers roughly the time span between the demise of the dinosaurs and beginnning of the most recent ice age. During the Tertiary the modern families of birds, mammals and flowering plants evolved . Marine invertebrates and marine vertebrates other than the marine mammals experienced only modest evolution.

Continental drift was modest. India broke loose from Africa and attached itself to Asia. South America attached itself to North America toward the end of the Tertiary. Antarctica -- which was already separate -- drifted to its current position over the South Pole. Climates during the Tertiary slowly cooled starting off tropical to moderate worldwide in the Paleocene and ending up with extensive glaciations at the end of the period.

The term Tertiary was first used by Giovanni Arduino, possibly in a letter dated 1759 (dates on the web vary). He classified geologic time into primitive (or primary), secondary and tertiary periods based on observations of northern Italy (some pages on the web add a forth type, variously quaternary, volcanic or alluvial). In 1828 Charles Lyell incorporated a Tertiary period into his own far more detailed system of classification. He subdivided the Tertiary period into four epochs according to the percentage of fossil mollusks that resembled modern species, using greek names: Eocene, Miocene, Older Pliocene and Newer Pliocene. Later the use of mollusks was abandoned from the definition and the epochs were renamed and redefined.

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