Mr. Ahearn Earth Science 2010 Geologic History Mr. Ahearn Earth Science 2010
Discovering Earth’s History Rocks record geological events and changing life forms of the past We have learned that Earth is much older than anyone had previously imagined. The surface and interior have been changed by the same geological processes that happen today
Discovering Earth’s History Principle of Uniformitarianism: The forces and processes happening today have been going on for a long time
Key Principles Tells us the sequence in which events occurred Relative Dating Tells us the sequence in which events occurred Law of Superposition In sedimentary rocks, each bed is older than the one above it and younger than the one below it
Law of Superposition Younger Layers→ Older Layers→
Ordering the Grand Canyon’s History Makes no sense without caption in book
Relative Dating Principles Principle of Original Horizontality • The principle of original horizontality means that layers of sediment are generally deposited in a horizontal position.
Disturbed Rock Layers Makes no sense without caption in book
Relative Dating Principles Cross-Cutting Relationships • The principle of cross-cutting relationships states that when a fault cuts through rock layers, or when magma intrudes other rocks and crystallizes, we can assume that the fault or intrusion is younger than the rocks affected. Inclusions • Inclusions are rocks contained within other rocks. • Rocks containing inclusions are younger than the inclusions they contain.
Applying Cross-Cutting Relationships Makes no sense without caption in book
Formation of Inclusions Makes no sense without caption in book
Relative Dating Principles Unconformities • An unconformity represents a long period during which deposition stopped, erosion removed previously formed rocks, and then deposition resumed. • An angular unconformity indicates that during the pause in deposition, a period of deformation (folding or tilting) and erosion occurred.
Formation of an Angular Conformity Makes no sense without caption in book
Relative Dating Unconformities • A nonconformity is when the erosional surface separates older metamorphic or intrusive igneous rocks from younger sedimentary rocks. • A disconformity is when two sedimentary rock layers are separated by an erosional surface.
A Record of Uplift, Erosion, and Deposition Makes no sense without caption in book
Complete Questions #1-15 Review Book p. 119-121
Correlation of Rock Layers Correlation is establishing the equivalence of rocks of similar age in different areas.
Correlation of Strata at Three Locations Makes no sense without caption in book
Fossils: Evidence of Past Life Remains or traces of prehistoric life Mainly found in sedimentary rock
Fossils: Evidence of Past Life The type of fossil that is formed is determined by the conditions under which an organism died and how it was buried. Unaltered Remains • Some remains of organisms—such as teeth, bones, and shells—may not have been altered, or may have changed hardly at all over time.
Fossils: Evidence of Past Life Altered Remains • The remains of an organism are likely to be changed over time. • Fossils often become petrified or turned to stone. • Molds and casts are another common type of fossil. • Carbonization is particularly effective in preserving leaves and delicate animals. It occurs when an organism is buried under fine sediment.
Fossils: Evidence of Past Life Indirect Evidence • Trace fossils are indirect evidence of prehistoric life. Conditions Favoring Preservation • Two conditions are important for preservation: rapid burial and the possession of hard parts.
Types of Fossilization Makes no sense without caption in book
Fossils: Evidence of Past Life The principle of fossil succession states that fossil organisms succeed one another in a definite and determinable order. Therefore, any time period can be recognized by its fossil content. Index fossils are widespread geographically, are limited to a short span of geologic time, and occur in large numbers.
Fossils: Evidence of Past Life Interpreting Environments • Fossils can also be used to interpret and describe ancient environments.
Overlapping Ranges of Fossils Makes no sense without caption in book
Complete Questions # 15-21 Review Book p. 122-124
The Geologic Time Scale
Precambrian All time between origin of Earth & 570 mya Rocks lack fossils Igneous & M/M Animals lacked hard parts Stromatolites
Paleozoic: Cambrian walking trilobite ©2000 Most of the major groups of animals first appear in the fossil record. "Cambrian Explosion“ Trilobite: index fossil Mostly marine animals
Paleozoic: Ordovician Increase in number & KINDS of animals All life in oceans Index fossil: graptolite Early molluscs Ended w/ Taconic Orogeny Green Mountains & Taconics (NY &VT)
Paleozoic: Silurian Similar life to Ordovician Plants on land Club mosses
Paleozoic: Devonian “Age of Fishes” Warm oceans Land plants multiplied True ferns Seed plants First forests Deer Isle, Maine
Paleozoic: Carboniferous Huge freshwater swamps Coal beds along Mississippi river 1st reptiles appeared More insects “The age of Cockroaches”
Carboniferous Rocks Back to Rocks of Ages Back to Rocks of Ages Back to Rocks of Ages Mississippian and Pennsylvanian Rocks Mississippian and Pennsylvanian Rocks Mississippian and Pennsylvanian Rocks Carboniferous Rocks
Folded Carboniferous Coal Beds
Paleozoic: Permian Dry Climate Inland coral reefs created Layers of evaporites Inland coral reefs created
Mesozoic: Triassic Extinction of many marine animals More gymnosperms Trilobites More gymnosperms Earliest dinosaurs
Mesozoic: Jurassic Earliest birds & mammals
Mesozoic: Cretaceous
Mesozoic: Cretaceous Earliest flowering plants Climax & extinction of dinosaurs 1st placental mammals
Mass Extinction
Cenozoic: Tertiary/Quaternary Early warm Later ice age Grand Canyon formed Modern mammals, animals & plants
Complete Questions # 22-51 Review Book p. 129-132
The End Or is it our future?