Eras geologic Of the Earth

Cenozoic Era

Dating from 65mya - present, the Cenozoic Era began with a truly big bang, a meteor crashing into the Earth, causing a mass extinction of the large, dominant life forms of the Mesozoic Era, the dinosaur. This event also marked the beginning the the Age of Mammals, as mammals slowly invaded those niches left open by the extinct dinosaurs. During this era, birds, angiosperms (flowers), insects, and bony fish proliferated through nearly every habitat on Earth.

Tertiary Period

Dating from 65-1.8mya, the Tertiary Period saw the early mammals, flowers, insects, and birds move into the open niches left by the extinct dinosaurs. During this period, the major families of these groups evolved. The early primates appeared during this time, dividing into lineages that led to our present monkeys, apes, and man. The branch that led to Homo sapien separated from the branch the led to the modern chimpanzee some 6mya.

Quaternary Period

We are in the Quaternary Period, which started 1.8mya. The Quaternary Period saw major changes in Earth's climate, beginning with a major glaciation that did not end until some 10,000 years ago. During this period, man moved more towards an agricultural based society, which led to the development of more complex tools.
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Terminology

The largest defined unit of time is the supereon, composed of eons. Eons are divided into eras, which are in turn divided into periods, epochs and ages. The terms eonothem, erathem, system, series, and stage are used to refer to the layers of rock that correspond to these periods of geologic time.

Geologists qualify these units as Early, Middle, and Late when referring to time, and Lower, Mid, and Upper when referring to the corresponding rocks. For example, the Lower Jurassic Series in chronostratigraphy corresponds to the Early Jurassic Epoch in geochronology.^[3] The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus "early Miocene" but "Early Jurassic."

Geologic units from the same time but different parts of the world often look different and contain different fossils, so the same period was historically given different names in different locales. For example, in North America the Lower Cambrian is called the Waucoban series that is then subdivided into zones based on succession of trilobites. In East Asia and Siberia, the same unit is split into Alexian, Atdabanian, and Botomian stages. A key aspect of the work of the International Commission on Stratigraphy is to reconcile this conflicting terminology and define universal horizons that can be used around the world.