Geologic Time The Rock and Fossil Record Geologic

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Geologic Time The Rock and Fossil Record

Geologic Time The Rock and Fossil Record

Geologic Time Scale n n time divisions Geologists use different ________ to keep track

Geologic Time Scale n n time divisions Geologists use different ________ to keep track of Earth’s history. These divisions are based on: q q n life forms present during the time Type of ______ period geologic changes occurring at the Type of ______ time. Geologic Time Scale – a record of Earth’s history, beginning 4. 6 bya, that shows events, time units, and ages.

Geologic Time Scale n There are three types of subdivisions of geologic time: q

Geologic Time Scale n There are three types of subdivisions of geologic time: q q q ERA – major subdivisions of time based on ______ differences in life-forms. Period _____ – subdivisions of eras based on types of life and geologic events (mountain building or plate movements). Epoch _____ – subdivisions of periods based on types of life and geologic events. (Epochs are found in the Cenozoic Era alone because the fossil records and rock layers are more complete for this time. )

Era Phane rozoic Eon Cenozoic Period Epoch Quaternary Recent Pleistocene Neogene Pliocene Miocene Paleogene

Era Phane rozoic Eon Cenozoic Period Epoch Quaternary Recent Pleistocene Neogene Pliocene Miocene Paleogene Oligocene Eocene Paleocene Mesozoic Cretaceous Jurassic Triassic Paleozoic Permian Pennsylvanian Mississippian Devonian Silurian Ordovician Cambrian Precambrian Time

Earths Story and Those Who First Listened. n uniformitarianism to Scientists use __________ interpret

Earths Story and Those Who First Listened. n uniformitarianism to Scientists use __________ interpret the past and predict the future. q n James Hutton 1795 – “Theory of Earth” present past The _______ is the key to the _____. q Things that happened now must have happened in the past.

n n n Uniformitarianism versus Catastrophism– equal to slow change Uniformitarianism Catastrophism – equals

n n n Uniformitarianism versus Catastrophism– equal to slow change Uniformitarianism Catastrophism – equals quick sudden changes. Which is right? q A little of both.

Relative Dating - Superposition n n Here’s a stack of newspapers collecting dust in

Relative Dating - Superposition n n Here’s a stack of newspapers collecting dust in the living room. Everyday as the paper is read it is put in the pile. Someone comes to you and asks about an article from last week. Where do you look?

Relative Dating? Which came first? n Geologists use relative Which layer is older? dating

Relative Dating? Which came first? n Geologists use relative Which layer is older? dating to determine the ______ relative age of objects. Principle of Superposition – younger layers lie above older layers in an undisturbed sequence of C rocks. A n B A

The Principle of Superposition n In an undisturbed layer of rock the oldest rock

The Principle of Superposition n In an undisturbed layer of rock the oldest rock BOTTOM and the youngest is is on the _______. TOP

The Principle of Superposition n Exceptions to the Principle include tectonic MOVE tilt, forces

The Principle of Superposition n Exceptions to the Principle include tectonic MOVE tilt, forces acting on the rocks to _______, ERODE fault, or _____ rock layers.

Original Horizontality: sedimentary layers are initially deposited in horizontal layers n The forces of

Original Horizontality: sedimentary layers are initially deposited in horizontal layers n The forces of reality beat up on the earth and break it into small pieces, which then wash down rivers to the ocean and settle out on the seafloor. In horizontal layers.

Relative Dating n Used by geologist to determine the order of events and the

Relative Dating n Used by geologist to determine the order of events and the relative age of rocks by their POSITION in the stack. ______

Relative Dating n n This image shows a stack of rocks with 3 different

Relative Dating n n This image shows a stack of rocks with 3 different types of rock and one fault. Which is the oldest?

Relative Dating n Here’s the sequence: A, B, fault, C C B B A

Relative Dating n Here’s the sequence: A, B, fault, C C B B A

Unconformities n n Rock layers are a record of past geologic events. INCOMPLETE because

Unconformities n n Rock layers are a record of past geologic events. INCOMPLETE because they are Most are ______ missing layers. If sediment stops being deposited and EROSION goes to work removing material _____ then you will have a gap in the record. These gaps are called UNCONFORMITIES _________.

Angular Unconformities

Angular Unconformities

Angular Unconformities

Angular Unconformities

Angular Unconformities

Angular Unconformities

Disconformity n No obvious evidence of missing rock layers UNEVEN surface caused by except

Disconformity n No obvious evidence of missing rock layers UNEVEN surface caused by except for an _____ erosion.

Nonconformity When sedimentary rock layers form above METAMORPHIC IGNEOUS ______ or intrusive ______ rock

Nonconformity When sedimentary rock layers form above METAMORPHIC IGNEOUS ______ or intrusive ______ rock layers. n The metamorphic or igneous rock is uplifted and eroded. n Sedimentary rocks are then deposited on top. n

Nonconformity Arrow points to contact of Cambrian Tapeats Sandstone on Precambrian Vishnu Schist.

Nonconformity Arrow points to contact of Cambrian Tapeats Sandstone on Precambrian Vishnu Schist.

Cross-cutting relationships: the OLDER thing being cut is ____ than the thing doing the

Cross-cutting relationships: the OLDER thing being cut is ____ than the thing doing the cutting n n n You can’t cut it if it isn’t there. Igneous intrusions: Dikes, Sills, Batholiths, Laccoliths

Cross-cutting Relationships

Cross-cutting Relationships

Fossils

Fossils

Fossils n Definition: q Fossil – the remains, imprints, or traces of onceliving organisms,

Fossils n Definition: q Fossil – the remains, imprints, or traces of onceliving organisms, usually preserved in rock, that tell us when, where, and how those organisms lived.

Fossils n n Fossils help scientists determine when and where plants and animals lived.

Fossils n n Fossils help scientists determine when and where plants and animals lived. Also, how they lived.

Fossil Formation n Necessary Conditions: q The body of a dead organism must be

Fossil Formation n Necessary Conditions: q The body of a dead organism must be protected from scavengers and microorganisms. n Quick Burial (sediments from floods, landslides, ________ etc. ) Hard Parts ________ (bones, shells, or teeth) n Sedimentary Rocks _____________ Fossils typically do not n withstand the heat and pressure involved in forming igneous and metamorphic rocks. q Limestone, Shale, Sandstone are examples NEARLY ALL FOSSILS ARE FOUND IN SEDIMENTARY ROCK

Fossil in Virginia Appalachian Plateau Valley & Ridge Coastal Plain Why not the Blue

Fossil in Virginia Appalachian Plateau Valley & Ridge Coastal Plain Why not the Blue Ridge and Piedmont?

Fossil in Virginia Era Period Epoch Cenozoic Quaternary Recent Pleistocene Tertiary Pliocene Miocene Oligocene

Fossil in Virginia Era Period Epoch Cenozoic Quaternary Recent Pleistocene Tertiary Pliocene Miocene Oligocene Eocene Paleozoic, Mesozoic, and Cenozoic fossils are found in Virginia Paleocene Mesozoic Cretaceous Jurassic Triassic Paleozoic Permian Pennsylvanian 544 mya – present Paleozoic Mesozoic Cenozoic Mississippian Devonian Silurian Ordovician Cambrian Precambrian Time

Petrified Remains n Some or all of the original materials in the remains have

Petrified Remains n Some or all of the original materials in the remains have been replaced by minerals.

Carbonaceous Films n n n The tissues of most organisms are made of compounds

Carbonaceous Films n n n The tissues of most organisms are made of compounds that contain carbon. Sometimes that’s all that is left. Pressure and heat force gases and liquids from the body and leave an outline of the body.

Carbonaceous Films n Swamps and deltas where large amounts of plant matter areas in

Carbonaceous Films n Swamps and deltas where large amounts of plant matter areas in which these fossils are found.

Molds and Casts n n n Seashells or other hard parts fall into soft

Molds and Casts n n n Seashells or other hard parts fall into soft sediment such as mud and get buried. Compaction and sedimentation turn the sediments to rock. Pores in the rock let water and air reach the object and allow it to decay. The resulting void is called a mold. Other sediments may fill the mold and solidify into a cast.

Original Remains n n Sometimes the original remains are preserved. Insects trapped in amber

Original Remains n n Sometimes the original remains are preserved. Insects trapped in amber (crystallized resin) Ice men, mammoths Tar Pits

Trace Fossils n n n Fossilized tracks or other evidence of animal activity. Dino-tracks

Trace Fossils n n n Fossilized tracks or other evidence of animal activity. Dino-tracks Coprolites

Index fossils n n n Species inhabit Earth for a period of time before

Index fossils n n n Species inhabit Earth for a period of time before evolving into new species or dying out. Paleontologists use animals that exist for a short time period as index fossils. Index fossil – species that existed on Earth for a relatively ______ short period of time, were ___________ numerous wide-spread geographically.

Index fossils n Index fossils are used to determine the age of rock layers.

Index fossils n Index fossils are used to determine the age of rock layers. 200 Life Span (mya) A 500 - 200 B 400 - 200 C 400 - 300 400 500

Fossils and Ancient Environments n n environment Fossils also indicate the _______of an area

Fossils and Ancient Environments n n environment Fossils also indicate the _______of an area long ago. Remember Antarctic rocks contain fossils of tropical plants

Fossils and Ancient Environments n n Most VA fossils are of _________ marine organisms

Fossils and Ancient Environments n n Most VA fossils are of _________ marine organisms Brachiopod fossils indicate a shallow sea environment. Brach’s are found in the mountains of Virginia What can you conclude from this?

Absolute Dating n n numerical Absolute time places a _______ age on an event.

Absolute Dating n n numerical Absolute time places a _______ age on an event. Radioactive decay is used to determine _________ the absolute age of rocks.

Radiometric Dating n n Radiometric Dating – determining the age of a material by

Radiometric Dating n n Radiometric Dating – determining the age of a material by comparing the ratio of the ______ (undecayed) material to the parent daughter ______ (decayed) material. Example: A rock has an isotope that takes 10, 000 years to decay into half of the parent material. The half-live is 10, 000 years. Scientist examine the rock and find exactly half of the material is “parent” material and half is “daughter” material. Then the age of 10, 000 the rock has to be ________ years.

C

C