The Geologic Timescale A calendar of geologic time

1. The Geologic TimescaleA calendar of geologic time

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

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

4. 0 Ma C M Phanerozoic P 540 Ma Proterozoic 2500 Ma Archean 3800 Ma Hadean 4600 Ma Modern Geologic Time Scale Four Eons of Geologic Time

5. 0 Ma C M Phanerozoic P 540 Ma Proterozoic 2500 Ma Archean 3800 Ma Hadean 4600 Ma Modern Geologic Time Scale “Visible Life” “Earlier Life” “Ancient Eon” “Hidden Eon”

6. Modern Geologic Time Scale 0 Ma C M Phanerozoic Ma 0 P Holocene 540 Ma Quat. .01 Pleistocene 1.6 Pliocene Neogene 5 Miocene Cenozoic 23 Tertiary Oligocene 35 Paleogene Eocene Proterozoic 57 Paleocene RIP 65 Eons Cretaceous 146 Mesozoic Jurassic 208 Triassic 2500 Ma 245 Permian 290 Pennsylvanian Carb. 323 Mississippian Archean 360 Paleozoic Devonian 408 Silurian 439 Ordovician 3800 Ma 510 Cambrian 540 Hadean Quat. = Quaternary Carb. = Carboniferous 4600 Ma

7. Modern Geologic Time Scale 0 Ma C M Phanerozoic Ma 0 P Holocene 540 Ma Quat. .01 Pleistocene 1.6 Pliocene Neogene 5 Miocene Cenozoic 23 Tertiary Oligocene 35 Paleogene Eocene Proterozoic 57 Paleocene RIP 65 Eras Cretaceous 146 Mesozoic Jurassic 208 Triassic 2500 Ma 245 Permian 290 Pennsylvanian Carb. 323 Mississippian Archean 360 Paleozoic Devonian 408 Silurian 439 Ordovician 3800 Ma 510 Cambrian 540 Hadean Quat. = Quaternary Carb. = Carboniferous 4600 Ma

8. Modern Geologic Time Scale 0 Ma C M Phanerozoic Ma 0 P Holocene 540 Ma Quat. .01 Pleistocene 1.6 Pliocene Neogene 5 Miocene Cenozoic 23 Tertiary Oligocene 35 Paleogene Eocene Proterozoic 57 Paleocene RIP 65 Periods Cretaceous 146 Mesozoic Jurassic 208 Triassic 2500 Ma 245 Permian 290 Pennsylvanian Carb. 323 Mississippian Archean 360 Paleozoic Devonian 408 Silurian 439 Ordovician 3800 Ma 510 Cambrian 540 Hadean Quat. = Quaternary Carb. = Carboniferous 4600 Ma

9. Modern Geologic Time Scale 0 Ma C M Phanerozoic Ma 0 P Holocene 540 Ma Quat. .01 Pleistocene 1.6 Pliocene Neogene 5 Miocene Cenozoic 23 Tertiary Oligocene 35 Paleogene Eocene Proterozoic 57 Paleocene RIP 65 Epochs Cretaceous 146 Mesozoic Jurassic 208 Triassic 2500 Ma 245 Permian 290 Pennsylvanian Carb. 323 Mississippian Archean 360 Paleozoic Devonian 408 Silurian 439 Ordovician 3800 Ma 510 Cambrian 540 Hadean Quat. = Quaternary Carb. = Carboniferous 4600 Ma

10. 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.

11. Grand Canyon

12. Grand Canyon

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

14. time 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. youngest younger even less old less old oldest East Devonshire

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

16. 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 SE Coast of England

17. Cretaceous System D’Omalius d’Halloy, 1822

18. Regional correlation of chalk deposits based on lithology.

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

20. 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?

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

22. William Smith (1769-1839) surveyor, civil engineer

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

24. 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.

25. Goes Extinct Exists Evolves T I M E Unique interval of time

26. Goes Extinct Exists Evolves T I M E

27. T I M E

28. T I M E

29. Fossils are the key to correlating regional systems Great Britain Continental Europe

30. Geologic Systems and Geologic Time • 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.

31. 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.

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

33. 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.

34. Modern Geologic Time Scale 0 Ma C M Phanerozoic Ma 0 P Holocene 540 Ma Quat. .01 Pleistocene 1.6 Pliocene Neogene 5 Miocene Cenozoic 23 Tertiary Oligocene 35 Paleogene Eocene Proterozoic 57 Paleocene RIP 65 Cretaceous 146 Mesozoic Jurassic 208 Triassic 2500 Ma 245 Permian 290 Pennsylvanian Carb. 323 Mississippian Archean 360 Paleozoic Devonian 408 Silurian 439 Ordovician 3800 Ma 510 Cambrian 540 Hadean Quat. = Quaternary Carb. = Carboniferous 4600 Ma