The Geologic Timescale A calendar of geologic time

Millennium Century Decade Year Month Day Subdivisions of Human Time longer shorter

Eon Era Period Epoch Stage Substage Subdivisions of Geologic Time longer shorter

Modern Geologic Time Scale Hadean Archean Proterozoic Phanerozoic 3800 Ma 4600 Ma 2500 Ma 540 Ma 0 Ma M C P Four Eons of Geologic Time

Modern Geologic Time Scale Hadean Archean Proterozoic Phanerozoic 3800 Ma 4600 Ma 2500 Ma 540 Ma 0 Ma M C P “Hidden Eon” “Ancient Eon” “Earlier Life” “Visible Life”

Modern Geologic Time Scale Paleozoic Ordovician Cambrian Silurian Devonian Mississippian Pennsylvanian Permian Mesozoic Triassic Jurassic Cretaceous Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Cenozoic Tertiary Holocene Quat. Paleogene Neogene Carb. Quat. = Quaternary Carb. = Carboniferous Ma 65 RIP Hadean Archean Proterozoic Phanerozoic 3800 Ma 4600 Ma 2500 Ma 540 Ma 0 Ma M C P Eons

Modern Geologic Time Scale Paleozoic Ordovician Cambrian Silurian Devonian Mississippian Pennsylvanian Permian Mesozoic Triassic Jurassic Cretaceous Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Cenozoic Tertiary Holocene Quat. Paleogene Neogene Carb. Quat. = Quaternary Carb. = Carboniferous Ma 65 RIP Hadean Archean Proterozoic Phanerozoic 3800 Ma 4600 Ma 2500 Ma 540 Ma 0 Ma M C P Eras

Modern Geologic Time Scale Paleozoic Ordovician Cambrian Silurian Devonian Mississippian Pennsylvanian Permian Mesozoic Triassic Jurassic Cretaceous Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Cenozoic Tertiary Holocene Quat. Paleogene Neogene Carb. Quat. = Quaternary Carb. = Carboniferous Ma 65 RIP Hadean Archean Proterozoic Phanerozoic 3800 Ma 4600 Ma 2500 Ma 540 Ma 0 Ma M C P Periods

Modern Geologic Time Scale Paleozoic Ordovician Cambrian Silurian Devonian Mississippian Pennsylvanian Permian Mesozoic Triassic Jurassic Cretaceous Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Cenozoic Tertiary Holocene Quat. Paleogene Neogene Carb. Quat. = Quaternary Carb. = Carboniferous Ma 65 RIP Hadean Archean Proterozoic Phanerozoic 3800 Ma 4600 Ma 2500 Ma 540 Ma 0 Ma M C P Epochs

What records the passing of geologic time? Formation of rock layers Sediments are deposited over time in layers. Each layer traps and records information about the time during which it formed. Sedimentary layers are analogous to the pages that compose the book of Earth History.

Grand Canyon

Rock layers are grouped into formations and given formal names by geologists.

East Devonshire Problem - how do you determine the order in which rock layers formed? At a single place, layers can be ordered using the law of Superposition. oldest less old even less old younger youngest time

Primary Secondary Transitional Tertiary Diluvial post-Diluvial circa 1790 Flood Gravels Layers composed of unconsolidated sediment Rock layers with abundant fossils Partly crystalline rock layers with sparse fossils Crystalline rock Earth History, 1700’s

SE Coast of England Within a local region, rock layers can be correlated on the basis of their lithology (physical characteristics) to define a geologic system. NW Coast of France

Cretaceous System D’Omalius d’Halloy, 1822

Regional correlation of chalk deposits based on lithology.

Primary Secondary Transitional Tertiary Diluvial post-Diluvial circa 1790 Parisian gypsum beds London clay alluvium Sicilian strata English chalk Oolites Lias New Red Sandstone Muschelkalk - Trias Magnesian Limestone Coal Measures Mountain Limestone Old Red Sandstone Devonshire strata Wenlock Limestone Welsh Greywackes Parisian chalk Jura Mt. strata Perm strata circa 1820 gravels Crystalline (metamorphic) strata British Isles Continental Europe Geologic Systems

Correlation - the matching-up of rock layers between different places. We can put local rock layers in the correct time order because we can see how they are stacked on each other. We can use the physical features of rock layers to correlate them into a regional system. The Problem: How can we correlate different regional systems so that they are in the correct time order if we can’t directly match their layers?

Great BritainContinental Europe ? ? How can we correlate different systems if the layers cannot be correlated based on their physical features?

William Smith ( ) surveyor, civil engineer

Smith made the first large scale geologic map showing the distribution and order of rock layers in Great Britain.

In his work as a surveyor, Smith noticed that the rock layers seemed to contain a unique sequence of fossil species that appear and disappear through time. Even when the rocks look different, the sequence of fossils is always the same.

TIMETIME Evolves Goes Extinct Unique interval of time Exists

TIMETIME Evolves Exists Goes Extinct

TIMETIME

TIMETIME

Great BritainContinental Europe Fossils are the key to correlating regional systems

Once a particular regional system was formally named and its fossils described, other regional systems with the same fossils were correlated to it and given the same name. The original system names thus came to stand for particular intervals of geologic time. Geologic Systems and Geologic Time

For example, the Jurassic System was originally named for the rocks and fossils of the Jura Mountains between France and Switzerland. Now the Jurassic Period refers to the time interval during which the fossil species of the Jurassic System lived. Any rock layers with these fossils can be identified as Jurassic in age. Geologic Systems and Geologic Time

Primary Secondary Transitional Tertiary Diluvial post-Diluvial Parisian gypsum bedsLondon clay alluvium Sicilian strata English chalk Oolites Lias New Red Sandstone Muschelkalk - Trias Magnesian Limestone Coal Measures Mountain Limestone Old Red SandstoneDevonshire strata Wenlock Limestone Welsh Greywackes Parisian chalk Jura Mt. strata Perm strata circa 1790circa 1870 Modern Time Scale Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian Precambrian Quaternary gravels Crystalline (metamorphic) strata British Isles Continental Europe

How do we assign sedimentary layers to their correct place in time? fossils each time interval in Earth history is defined by a unique set of species that existed at that time. Species evolve, live for a short time, and go extinct. The same species never evolves twice (extinction is forever). Evolution provides a “biological calendar” that geologists use to keep track of time. Fossils allow us to put the individual scenes from Earth history into the correct order to tell the full story.

Modern Geologic Time Scale Paleozoic Ordovician Cambrian Silurian Devonian Mississippian Pennsylvanian Permian Mesozoic Triassic Jurassic Cretaceous Paleocene Eocene Oligocene Miocene Pliocene Pleistocene Cenozoic Tertiary Holocene Quat. Paleogene Neogene Carb. Quat. = Quaternary Carb. = Carboniferous Ma 65 RIP Hadean Archean Proterozoic Phanerozoic 3800 Ma 4600 Ma 2500 Ma 540 Ma 0 Ma M C P