A brief history of Geologic time.
The long period of time occupied by Earth's geologic history is known as geologic time. Formal geologic time runs from the beginning of the Archean Eon (4.0 billion to 2.5 billion years ago) to the present. The Hadean Eon, which runs from roughly 4.6 billion years ago (corresponding to Earth's beginning formation) to 4.0 billion years ago, is frequently included in modern geologic time scales. In effect, geologic time is the period of Earth's history represented and documented in the planet's rock strata.
The geologic time scale divides the earth's history into periods based on the types of life that existed at different times since the planet's inception. Geochronologic units are the names given to these divisions (geo: rock, chronology: time). The majority of organisms are discovered as fossils, which are the remains or evidence of an organism from the geologic past preserved in silt or rock. Without fossils, scientists might not have come to the conclusion that the world has a long history prior to humanity.
The following divisions make up the Geologic Time Scale:
Eons: The most extensive subdivision, based on the abundance of specific fossils.
Eras: The second-longest subdivision; characterised by significant changes in the fossil record.
Periods are defined by the forms of life that existed at the time.
Epochs are the smallest divisions of time; they are distinguished by variances in living forms and can differ from continent to continent.
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