Key Concept:
The geological timescale is a system used to divide Earth’s long history into manageable segments based on major physical and biological events.
Short Notes:
Earth’s history spans about 4.6 billion years and is divided into eons, eras, periods, and epochs. These divisions help geologists and geographers understand the sequence of natural events, such as mountain formation, mass extinctions, and continental shifts.
The Precambrian is the earliest and longest span, including the formation of the Earth, early oceans, and the appearance of the first life forms. The Phanerozoic Eon, which includes the Paleozoic, Mesozoic, and Cenozoic Eras, contains most of Earth’s fossil record.
Each era is marked by important developments. For example, the Mesozoic Era is known as the age of reptiles and includes the breakup of Pangaea. The Cenozoic Era is the most recent and includes the formation of present-day continents and the rise of humans.
Key Terms:
- Geological Timescale – A chronological record of Earth’s history,
- Eon – The largest division of geological time,
- Era – Subdivision of an eon marked by major events,
- Period – A unit within an era,
- Epoch – A smaller division of a period,
- Precambrian – Earliest part of Earth’s history,
- Phanerozoic – Eon with visible fossils and complex life forms.
Example:
During the Cenozoic Era, the East African Rift Valley began forming — a sign of active tectonic movement still shaping the region today.
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