OverviewLearn below about the ages of important events in the fossil record and Earth's history during different geologic time intervals. Associated maps show the distributions of rocks from each time interval at or just below Earth's surface. Note that ages are maximum values and that some exposures end at state lines, indicative of differing age assignments by different institutions (e.g., state geological surveys). Show
Abbreviations:
Additional resources:
Credits: This page by Jonathan R. Hendricks for the [email protected] project. The maps were created using QGIS and USGS data from Horton et al. (2017) using the maximum age values for each mapped unit. All images have a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license. You are welcome to use them for any non-commercial educational purpose. Updates: Page last updated March 21, 2022. The geologic time scale. Image by Jonathan R. Hendricks for the [email protected] project. Note that the geologic time scale above is not scaled to time and mostly represents the Phanerozoic Eon. Mosts of geologic history (88%) happened during the Precambrian, which is represented by Hadean, Archean, and Proterozoic eons. The eons of geologic time and their relative proportions of total geologic time. Image by Jonathan R. Hendricks for the [email protected] project. Phanerozoic Eon: 541 to 0 myaName means "visible life." Most fossils are known from this time interval. All time before the Phanerozoic is assigned to the Precambrian, which is comprised of the Hadean, Archean, and Proterozoic eons. Cenozoic Era: 66 to 0 myaName means "new life." Fossil Record:
Earth History:
Quaternary Period: 2.6 to 0 MaThe earliest geologic time scale had four intervals: Primary (first), Secondary (second), Tertiary (third), and Quaternary (fourth). Only the Quaternary remains a valid period. Epochs include the Pleistocene and the Holocene. Fossil Record:
Earth History:
Neogene Period: 23 to 2.6 MaFormerly part of the Tertiary Period. Epochs include the Miocene and Pliocene. Fossil Record:
Earth History:
Paleogene Period: 66 to 23 MaFormerly part of the Tertiary Period. Epochs include the Paleocene, Eocene, and Oligocene. Fossil Record:
Earth History:
Cretaceous Period: 145 to 66 MaNamed for extensive accumulations of chalk that formed during this time. Fossil Record:
Earth History:
Jurassic Period: 201 to 145 MaNamed for the Jura Mountains (Alps). Fossil Record:
Earth History:
Triassic Period: 252 to 201 MaNamed for a three-part series of rocks in Germany. Fossil Record:
Earth History:
Paleozoic Era: 541 to 252 MaName means "old life." Fossil Record:
Earth History:
Permian Period: 299 to 252 MaNamed for the Russian city of Perm. Fossil Record:
Earth History:
Carboniferous Period: 359 to 299 MaNamed for the abundant carbon-rich coals that are known from this interval of geologic time. This period is commonly recognized as consisting of two sub-periods: the Mississippian and the Pennsylvanian. Pennsylvanian Subperiod: 323 to 299 MaNamed for the state of Pennsylvania. Fossil Record:
Earth History:
Mississippian Subperiod: 359 to 323 MaNamed for the Mississippi River Valley. Fossil Record:
Earth History:
Devonian Period: 419 to 359 MaNamed for Devon, England. The Devonian is also called the "age of fishes" due to the evolutionary radiation of fish species at this time. Fossil Record:
Earth History:
Silurian Period: 444 to 419 MaNamed for the Silures, an ancient Celtic tribe that lived in what is now Wales, United Kingdom. Fossil Record:
Earth History:
Ordovician Period: 485 to 444 MaNamed for the Ordovices, an ancient Celtic tribe that lived in what is now Wales, United Kingdom. Fossil Record:
Earth History:
Cambrian Period: 541 to 485 MaNamed for Cambria in Wales, United Kingdom. Fossil Record:
Earth History:
Precambrian: 4.54 Ga to 541 MaThe Precambrian is not a formal interval of geologic time. It represents all of Earth history prior to beginning of the Phanerozoic Eon. It was once thought that Precambrian rocks were devoid of fossils, but we now know that is incorrect. Fossil Record:
Earth History:
Proterozoic Eon: 2.5 Ga to 541 MaName means earlier ("protero-") life ("-zoic"). Fossil Record:
Earth History:
Archean Eon: 4.0 to 2.5 GaName from the Greek word arkhē, which means the beginning or origin. Fossil Record:
Earth History:
Hadeon Eon: 4.54 to 4.0 GaNamed for Hades, the mythological Greek underworld. There are no Hadean-aged rocks. Fossil Record:
Earth History:
How does the geologic time scale relate to evolution?Explanation: "The relative ages of the rocks in the geological column are determined by the remains of the organisms that they contain. " The Geological Column in turn is used to establish and support the Darwinian model of the theory of organic evolution. That is descent with modification.
Why are fossils recorded in the geologic time scale said to be incomplete?The fossil record, however, is quite incomplete. Here's one major reason why: Sediment has to cover an organism's remains in order for the long fossilization process to begin. Most organisms decompose before this can happen.
|