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EASC 212: PALEONTOLOGY
Geological time scale: Eras and Periods
Eons, eras, periods, and epochs are the four main subunits of the geologic time scale. The longest unit of geologic time is an aeon, and there have only ever been four of them. The three ages that span the beginning of the Cambrian period to the formation of the Earth itself are collectively referred to as the Precambrian. During this extraordinarily long period of time, which lasted for at least four billion years, the Earth's geosphere, atmosphere, and hydrosphere were formed along with its biosphere. Paleozoic Era (from 541-251 million years ago)
The Paleozoic era was characterized by the first appearance of multicellular organisms. These organisms were simple compared to modern day animals. There were no true land plants, only algae. Most marine invertebrates existed. Mesozoic Era (251-66 million years ago) During the Mesozoic era, the continents began to separate. This led to the formation of many mountain ranges and eventually the rise of the Himalayas. Many dinosaurs roamed the Earth including the famous T Rex. Cenozoic Era (65 million years ago - present) The Cenozoic era saw the evolution of mammals, birds, reptiles, amphibians, fish, insects, and flowering plants. Humans evolved around 2 million years ago. Anthropogenic Era (since 1750) Humans have been changing the environment since they started farming and making weapons. Since then, humans have had a great effect on climate change. Carboniferous Period (359-299 million years ago) This was the first period of time where there were no dinosaurs. There were many different types of animals including fish, amphibians, reptiles, birds, mammals, insects, and even some early flowering plants. The carboniferous period ended with the Permian extinction event.
Oligocene period began with the eocene period and ended with the Miocene period. Many different animals lived during this period including reptiles, insects, fish and flowering plants. Quaternary Period (from 1.8 million years ago - present) This period is divided into two subperiods: Pleistocene and Holocene. The Pleistocene was marked by glaciation and the extinction of many species. The Holocene is the current epoch.
