The chapter discusses the development and key features of the Geologic Time Scale (GTS2004), which integrates stratigraphic and geochronologic information. The scale is constructed through a series of steps, including standardization of chronostratigraphic units, calibration of linear time using radiometric and astronomical methods, and interpolation of data where direct information is insufficient. The scale aims to provide a more accurate and detailed representation of Earth's geological history, particularly in the Precambrian and Neogene periods. - **Precambrian**: The Precambrian period, spanning 88% of Earth's history, is defined by arbitrary absolute ages, which are criticized for being divorced from the rock record. The chapter proposes a "natural" time scale that defines boundaries at key events and transitions, using multiple geochronometers to calibrate stratigraphic boundaries. - **Neogene**: The Neogene period, from 23 Ma to the present, is the most detailed segment of the scale due to high-resolution radiometric dating and astronomical tuning. The scale is based on cyclic sedimentary successions and provides unprecedented accuracy and resolution for paleoclimatic and paleoceanographic studies. The chapter also outlines future challenges and improvements needed in time scale construction, including the formal definition of all Phanerozoic stage boundaries, orbital tuning for the entire Cenozoic and Cretaceous, and the resolution of zircon controversies. The next version of the Geologic Time Scale is planned for 2008, concurrent with the completion of boundary-stratotype definitions for all international stages.The chapter discusses the development and key features of the Geologic Time Scale (GTS2004), which integrates stratigraphic and geochronologic information. The scale is constructed through a series of steps, including standardization of chronostratigraphic units, calibration of linear time using radiometric and astronomical methods, and interpolation of data where direct information is insufficient. The scale aims to provide a more accurate and detailed representation of Earth's geological history, particularly in the Precambrian and Neogene periods. - **Precambrian**: The Precambrian period, spanning 88% of Earth's history, is defined by arbitrary absolute ages, which are criticized for being divorced from the rock record. The chapter proposes a "natural" time scale that defines boundaries at key events and transitions, using multiple geochronometers to calibrate stratigraphic boundaries. - **Neogene**: The Neogene period, from 23 Ma to the present, is the most detailed segment of the scale due to high-resolution radiometric dating and astronomical tuning. The scale is based on cyclic sedimentary successions and provides unprecedented accuracy and resolution for paleoclimatic and paleoceanographic studies. The chapter also outlines future challenges and improvements needed in time scale construction, including the formal definition of all Phanerozoic stage boundaries, orbital tuning for the entire Cenozoic and Cretaceous, and the resolution of zircon controversies. The next version of the Geologic Time Scale is planned for 2008, concurrent with the completion of boundary-stratotype definitions for all international stages.