Ca Geology Chp 3

Front 1

Until the 1950s, it was not possible to determine the actual numerical age of a rock or sediment. Geologists relied on a scheme of ____, which enabled them to order rock formations from oldest to youngest.

Back 1

Relative age dating

Front 2

Geologists use four principles to determine the relative order of geologic events in an exposed section of rocks or sediments. What are they?

Back 2

Principle of superposition

Principle of original horizontality

Principal of cross-cutting relations

Principal of inclusions

Front 3

This principle states: In an undisturbed sequence of layered materials, the layers at the bottom are oldest and the layers of the top are youngest.

Back 3

Principle of superposition

Front 4

This principle states: Sediments are originally deposited in horizontal, or nearly horizontal layers.

Back 4

Principle of original horizontality

Hint 4

Sediments accumulate in low-energy, gently sloping, or level environments.

Front 5

What information can we concluded about the 2nd and 3rd picture?

Back 5

Second picture: tilting and folding must have occurred after the rocks were deposited.

Third picture: A period of erosion occurred after the tilting, forming a relatively horizontal surface, and the sediments on that surface are younger than the erosional period.

Front 6

A rock unit or feature such as a fault that cuts through a layer of rock must have formed after that rock layer was formed.

Back 6

Principle of cross cutting relations

Front 7

A rock or sediment containing fragments of other rocks must be younger than the rock it contains. (the inside rock is older)

Back 7

Principle of inclusions

Hint 7

Ex. lava might incorporate pieces of rock from the sides of a fissure as it erupts. The resulting volcanic rock will contain inclusions of the older incorporated rock.

Front 8

The landscape is younger than any of the rock or sediment beneath it. Hills, valleys, & plains have been sculpted on the materials beneath them, and the forces of erosion & deposition that shape the landscape are constantly reshaping the landscape.

Back 8

NO QUESTION. Exx. If a fault causes displacement of a landscape features such as a stream, it is most likely an active fault, but if a sedimentary deposit buries a fault, then the fault has not moved since the layered form.

Front 9

Many sedimentary & metasedimentary rocks contain ___, remains of plants & animals, that can aid geologists in assigning ages to the rock. They can be found from rocks formed in every conceivable environment that supports life, but the majority are the remains of ___ life since covers most of the earth and low-lying areas where sediments can easily accumulate.

Back 9

fossils; marine

Hint 9

Low energy terrestrial environments (lake beds, peat bogs, marshes) common fossil places too. Species with hard parts easily preserved. Environments with rapid burial great for fossils.

Front 10

___ is the study of ancient life. Systematically collect & classify fossiles and pieced together successions of life forms represented in the fossil record.

Back 10

Paleontology

Front 11

Although some species have persisted through long stretches of geologic time without many change, others made only brief appearance on Earth. The presence of these time-specific, characteristic ___ is particularly useful. Helps to identify rocks formed during the same restricted time interval, even if the rocks are found in widely separated areas.

Back 11

index fossils

Front 12

Paleontologists created geologic time scale based on evolutionary sequence of species through time. Broken into __ where boundaries are marked by first appearances of groups of species and sudden, catastrophic extinstions and further separated into ___ then ___.

Back 12

eras; periods, epochs

Hint 12

Weird names come from people and places where best example of those marks. Ex. Ordovice Celtic people of Wales

Front 13

Unstable forms of elements referred as ____ break down spontaneously to more more stable atoms giving off energy in the form of radiations. This breakdown process is ___.

Back 13

Radioactive isotopes; radioactive decay

Front 14

Radioactive decay takes place at a specific & constant rate, as does the buildup of the products of decay. The time it takes for half of the initial amount of radioactive material to decay is the ___ of that particular isotope.

Back 14

half-life

Front 15

Knowing the original amount of radioactive isotope in a rock, sediment, or fossil, and knowing its half-life, one can calculate the amount of time since the radioactive "clock" began ticking. The use of isotopes to date Earth materials is known as ___.

Back 15

radiometric dating

Front 16

A radiometric dating method commonly used for dating materials that are geologically young uses ___, a naturally occurring radioactive isotope of carbon produced when cosmic rays bombard nitrogen in the upper atmosphere. A fixed amount is in all living tissues, even us. When organism dies, it decays. Knowing that the half-life is 5,730 years, one can measure the amount of ___ in formerly living material and calculate the time that has passed since it died.

Back 16

carbon-14; carbon-14

Hint 16

After 50,000 years amount remaining so small, it can't be measured accurately so only used to date recent materials & events. Ex. wood, bone, shell, charcoal, soil. Also used heavily to determine sediments formed by floods, earthquakes, etc.

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Front 17

The "workhorse" of radiometric dating techniques for most rocks & geologic events is ___. Works best on igneous rocks. Measures time that has passed since the rock crystallized from magma or lava or cooled after metamorphism. half-life 1.3 billion years so can be used on all but the youngest geologic materials. Most common technique involves measuring buildup of argon-40, a gas, in rocks.

Back 17

potassium-argon (K-AR)

Hint 17

By finding localities where sedimentary rocks containing key fossil assemblages are in contact with ancient lava flows, K-Ar has helped add numbers to the geologic time scale. Other common radiometric dating uses uranium lead and rubidium strontium isotopes.
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Front 18

Rocks of pre-Mesozoic age relative rare in CA, so fossils of Paleozoic era restricted. Mesozoic rocks mostly marine fossils because most of CA's Mesozoic sedimentary & metasedimentary rocks were deposited in marine environments.

Back 18

Cenozoic rich & diverse. Home to some of N. America's richest late Cenozoic terrestrial fossil finds.

Front 19

___ fossils in CA only found in ___& Sierra Nevada & Klamath Mountain provinces. 95 species of ___, ocean dwelling arthropods invertebrate good index fossil for this time. Graphtolite, colonial small skeletons dashes rods important index fossil for Orodovician & Silurian rocks. __ rocks more widespread in CA than rocks from earlier Paleozoic periods. Can find coral, Fusilinids, Crinoids, & brachiopods.

Back 19

Paleozoic; Southeastern; Trilobites; Permian

Front 20

___ marine fossils common. CA wasn't much land so erosion carried most of dinosaurs away, but some rare bones from dinosaurs found in marine sedimentary rocks. Microscopic fossils of __ have proved to be among the most useful fossils of this time because can be recognizable even after metamorphism. Single-celled protozoans. Allows people to learn more about origins of CA's accreted oceanic terranes. ___ floating plant w/ silica important because likely source of much of CA's petroleum.

Back 20

Mesozoic; radiolaria; Diatoms

Hint 20

Mollusks, ammonites, turritella, Buchia, hypsilophodonts (duck bill group), Sarolophus, plesiosaur, ichtyosaur, footprint. Formaminifera single celled protozoan w/ shell of calcium carbonate microfossil.

Front 21

___ much of CA emerged from the sea creating land and era of the mammals. Oldest known land animal fossils in N. CA in Blackhawk Ranch. Irvington areas has a lot. California fossil locality best known to nongeologists is the ___ tar pools part of Hancock Park in LA. Natural pools of tar trapped animals and plants of all kinds.

Back 21

Cenozoic; Rancha La Brea

Hint 21

Ex. deer, camels, horse, saber-toothed tigers, wolf, oldest mammoth elephant. Diatoms, forminifera.

Front 22

__ and ___ provide info about water temperature, salinity, depth, amount of light. Ex. solitary corals found in 80,000 old sediments in marine terraces off South CA. These are found only in North CA today indicating water temperatures were once cooler in South CA.

Back 22

Diatoms and foraminifera

Front 23

CA's official state fossil is?

Back 23

The saber-tooth tiger, Smilodon