8.E.6A.1 Develop and use models to organize Earth’s history (including era, period, and epoch) according to the geologic time scale using evidence from rock layers.
Units of Geologic Time |
Learning Objectives:
Students will be able to recognize the relationship among the units – era, period, and epoch – into which the geologic time scale is divided.
Students will be able to recognize the relationship among the units – era, period, and epoch – into which the geologic time scale is divided.
It is essential for you to know that the geologic time scale divides Earth’s long history into units of time:
> eras are divided into periods
> periods can be further divided into epochs
Major information found on the geologic time scale includes:
> Precambrian is the name given to the earliest span of time in Earth history.
> Geologists divide the time between Precambrian and the present into three long units called eras (Paleozoic, Mesozoic, Cenozoic).
> The names of the eras are important, as is the order from oldest era to most recent.
> Eras are subdivided into units called periods.
> Cambrian being the first period is important.
> With a more complete fossil record available, the periods of the Cenozoic era are subdivided further into epochs.
> Present day Earth is in the Cenozoic era and the Quaternary period in the Holocene epoch.
> Geologic time has not ended.
> eras are divided into periods
> periods can be further divided into epochs
Major information found on the geologic time scale includes:
> Precambrian is the name given to the earliest span of time in Earth history.
> Geologists divide the time between Precambrian and the present into three long units called eras (Paleozoic, Mesozoic, Cenozoic).
> The names of the eras are important, as is the order from oldest era to most recent.
> Eras are subdivided into units called periods.
> Cambrian being the first period is important.
> With a more complete fossil record available, the periods of the Cenozoic era are subdivided further into epochs.
> Present day Earth is in the Cenozoic era and the Quaternary period in the Holocene epoch.
> Geologic time has not ended.
Eon > Era > Period > Epoch
Precambrian EraIncludes the beginning and formation of Earth 4.6 Billion years ago - about 543 million years ago. Approximately 87% of Earth's history.
> Includes the formation of the Earth.
> Includes approximately 87% of Earth’s history. > According to the fossil record in the beginning of the Precambrian eon, there was no life on Earth yet. > Not many fossils are found in the fossil record > According to the fossil record life on Earth started in the oceans about 3.5 billion years ago. Mesozoic Era
> Reptiles were the dominant animals of this era, including the various dinosaurs.
> Small mammals and birds also appeared. > Toward the end of the era, flowering plants appeared and the kinds of mammals increased. > The mass extinction that ended the era caused the dinosaurs to become extinct. |
Paleozoic Era
> Began with the early invertebrates, such as trilobites and brachiopods; continued to develop early vertebrate fish, then arachnids and insects; later came the first amphibians, and near the era’s end the reptiles became dominant.
> Early land plants included simple mosses, ferns, and then cone-bearing plants. > By the end of the era, seed plants were common. > The mass extinction that ended the era caused most marine invertebrates as well as amphibians to disappear.
Cenozoic Era
> New mammals appeared while others became extinct.
> The diversity of life forms increased. > Flowering plants became most common. > Humans are also part of the most recent period of this era.
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