Final answer:
The geologic time scale divides Earth's history into eons, eras, periods, epochs, and ages, starting with the Earth's formation around 4.54 billion years ago. We are currently in the Phanerozoic eon, Cenozoic era, and Quaternary period. This division helps to organize Earth's history based on major geological and biological events.
Step-by-step explanation:
Geologic Time Scale Divisions
The geologic time scale is an essential tool in understanding Earth's history, subdividing it into major chunks that reflect transformative events in geology, climate, and the evolution of life. The Earth formed during the Hadean eon, and we are currently in the Phanerozoic eon, specifically in the Quaternary period of the Cenozoic era. The geologic time scale includes eons, which are the broadest subdivisions, followed by eras, periods, epochs, and ages in descending order of scale.
Geologic time began with the formation of Earth around 4.54 billion years ago (bya), first divided into four eons: the Hadean, Archean, Proterozoic, and Phanerozoic; the first three often grouped as the Precambrian. The Phanerozoic eon is then further divided into three eras: the Paleozoic, Mesozoic, and Cenozoic. Each era is further divided into periods, and periods into epochs and ages. For instance, the Cenozoic era consists of the Paleogene, Neogene, and Quaternary periods. The current period, the Quaternary, includes the Holocene epoch, which is our current epoch.
The subdivisions of geologic time on the geologic time scale are color-coded for easy reference, with golden spikes indicating specific places used to define age boundaries. These divisions are based on significant events like tectonic shifts, biological milestones, and climate changes, with numerical ages derived from radiometric dating techniques.