The geological time scale is organized into several hierarchical divisions that represent the history of the Earth and its biological evolution. Here's how it's structured:
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Eons: The largest time units, divided into:
- Hadean: Formation of the Earth and the earliest geological history (about 4.6 to 4.0 billion years ago).
- Archean: The development of the Earth's crust and the emergence of the earliest known life forms (about 4.0 to 2.5 billion years ago).
- Proterozoic: The appearance of more complex life forms and significant geological changes (about 2.5 billion to 541 million years ago).
- Phanerozoic: The time of abundant fossil evidence, divided into three major eras: Paleozoic, Mesozoic, and Cenozoic (541 million years ago to present).
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Eras: Each eon is further divided into eras:
- Paleozoic Era: Marked by the explosion of marine life and the colonization of land (541 to 252 million years ago).
- Mesozoic Era: Known as the age of reptiles, including dinosaurs (252 to 66 million years ago).
- Cenozoic Era: The age of mammals and birds, leading to the present (66 million years ago to the present).
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Periods: Each era is divided into periods that reflect significant geological or paleontological events. For example, the Paleozoic includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.
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Epochs: Periods are further divided into epochs to represent shorter intervals significant for evolutionary changes. For instance, the Cenozoic Era includes the Paleogene, Neogene, and Quaternary epochs.
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Ages: The smallest division, which represents specific time frames within epochs.
The geological time scale is based on stratigraphy, fossil records, and radiometric dating, providing a framework for understanding Earth's history and the evolution of life in relation to geological events.
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