Geologic Time

Geologic Time and Geologic Column

Geologic Time Eons Eras Periods Epochs

Eons There are 2 Major Eons Precambrian Phanerzoic

The Precambrian Precambrian Rocks represent 87% of Earth History From 4.5 Byrs to 544 Myrs ago Majority-Igneous, Metamorphic, and some undeformed sedimentary rocks

Phanerozoic Eon Contains the Paleozoic, Mesozoic, and Cenozoic Eras 544 Myrs to present

Paleozoic Era Existed 544 Myrs to 248 Myrs ago Contains the Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian Periods

Mesozoic Era 248 Myrs to 65 Myrs ago Contains the Triassic, Jurassic and Cretaceous Periods Great Time of Change

Cenozoic Era 65 Myrs ago to Present Contains the Tertiary and Quaternary Periods It is the here and now

Concepts Relative Time Absolute Age Law of Original Horizontality Law of Superposition Law of Original Continuity Law of Faunal Assemblages

Concepts: Continued Law of Faunal Succession Law of Crosscutting Relationships Law of Incusions Law of Unconformities

Relative Time vs. Absolute Age Relative Age is determined using a Geologic Column. How do rock strata or layers relate to each other. Absolute Age is determined through radioactive dating and gives an “absolute” age of the rock.

Creating A Geologic Column We must obey the previous stated laws Using the laws we can reconstruct geologic Obey events by constructing a geologic column

The Laws Law of Original Horizontality: All sediments laid down in water are horizontal or near horizontal. Law of Superposition: Undisturbed sedimentary rocks are older at the bottom of the formation and younger at the top.

The Laws Continued Law of Original Continuity: Sedimentary rocks exist laterally until the thin or pinch out at their margins. Law of Faunal Assemblages: Plants and Animals of the same age will exist together within the rocks.

Laws Continued Law of Faunal Succession: Different geologic formations of different ages will have different fauna. Law of Crosscutting Relationships: Any rock cutting another must be younger that the one it cuts.

Crosscutting

Last Two Laws Law of Inclusions: Fragments of another rock in another rock are older than the rock they are in. Law of Unconformities: Rocks above the unconformity are younger than the ones below it.

What do we have here?

Let’s Apply This Now

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Geologic Time

by David Prindle on Dec 30, 2009

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Geologic Time — Presentation Transcript