The geologic time scale was formed by scientists studying rock layers and fossils found in different locations around the world. They noticed that certain fossils were always found in specific layers of rock and that similar rocks and fossils could be found in different locations. This led them to understand that the rocks and fossils could be used to determine the relative ages of different layers and create a timeline of Earth's history.
The geologic time scale is organized into different units of time called eras, periods, and epochs. The largest division is the eon, which is further divided into eras. Each era is then divided into shorter periods, which are further divided into epochs. The scale starts with the Precambrian eon, followed by the Phanerozoic eon, which is divided into the Paleozoic, Mesozoic, and Cenozoic eras.
During the Precambrian time, several processes changed the Earth's environment. One of the most significant was the development of photosynthetic organisms, such as cyanobacteria, which released oxygen as a byproduct of photosynthesis. This led to the oxygenation of Earth's atmosphere and the subsequent diversification of life forms. Other processes during Precambrian time included the formation and breakup of supercontinents, volcanic activity, the evolution of multicellular organisms, and the development of complex ecosystems.
Think about how the geologic time scale was created and how it is divided. Then answer the following questions.
How did scientists form the geologic time scale?
How is this scale organized?
What processes changed the Earth's environment during Precambrian time?
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