Absolute and Relative Dating Flashcards
how did early scientists explain geologic changes on earth
catastrophism
the principle that states that all geologic change occurs suddenly.
* Supporters of this thought that Earth’s features, such as mountains and seas, formed during sudden events called
catastrophes.
catastrophism
About 250 years ago, James Hutton established
a principle that is now known as
uniformitarianism
the idea that the same geologic processes that shape Earth today have been at work throughout Earth’s history
- The principle also states that the average rate of geologic change is slow and has remained relatively constant over time. (weathering, erosion, deposition, magmatism/volcanism, metamorphism, diastrophism, deformation (joints, fault, fold), earthquake)
- helps further understand what happened in the past
uniformitarianism
true/false
- Today, geologists realize that neither uniformitarianism nor catastrophism alone accounts for all geologic change. It is the combination of the two ideas.
- While most geologic change is gradual and uniform,
catastrophes do cause some geologic change. - For example, earthquakes, floods, volcanic eruptions, and asteroid impacts can cause sudden changes to Earth’s surface.
true
how do we tell the age of rock
through relative and absolute dating
what type of dating
- Relative age: comparing which is younger or
older; Qualitative - the science of determining the relative order of past events, w/o necessarily determining their absolute age
- used to arrange geological events, and the rocks they leave behind in a sequence
- utilizes laws of statigraphy
relative dating
branch of geology concerned with the order and relative position of strata and their relationship to the geological time scale
- analysis of the order and position of layers of archaeological remains
statigraphy
what is the term for each stripe of rock
layer/rock stratum/strata
How are rock strata formed?
- weathering and erosion (happens above water, when there is an uplift in the form of faults and folds)
- deposition
- Sedimentation- Compaction and Cementation
(Lithification; happens underwater)
the process that loose and underconsolidated Sediment particles transform into hard and solid rocks. This process includes a number of geological processes, such as consolidation, deep bury, cementation, recrystallization and dehydration.
lithification of sedimentary rocks
“lithification” of igneous rocks
cooling/crystallization of magma/lava
“lithification” of metamorphic rocks
metamorphism (heat, pressure, protolith, liquid)
principles of stratigraphy
- Law of Superposition
- Law of Original Horizontality
- Law of Lateral Continuity
- Law of Cross-cutting Relationships
- Law of Inclusion
- Law of Fossil Succession
principle of stratigraphy
a major principle of stratigraphy stating that within a sequence of layers of sedimentary rock, the oldest layer is at the base and that the layers are progressively younger with ascending order in the sequence.
law of superposition
principle of stratigraphy
suggests that all rock layers are originally laid down (deposited) horizontally and can later be deformed. (due to gravity)
- parallel to the horizon
- deposition first before deformation
law of original horizontality
principle of stratigraphy
- states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.
- materials forming any stratum were continuous unless some other bodies/erosion & weathering/endogenic (appeared after deposition) processes stood in the way
principle of lateral continuity
principle of stratigraphy
Any geologic feature that crosscuts or modifies another feature must be younger than the rocks it cuts through. The cross-cutting feature is the younger feature because there must be something previously there to cross-cut.
principle of cross-cutting relationship
principle of stratigraphy
any rock fragments that are included in a rock must be older than the rock in which they are included
- for any material to be included within the rock, it must have been present the time the rock layer was being lithified
- once a rock is lithified, no other material can be deposited within its internal structure
principle of inclusion
principle of stratigraphy
law of superposition, but fossils
- using this, one can determine stratigraphic succession - the order in which units of rock were deposited over time
principle of fossil succession
group of fossils
fossil assemblages
who proposed the first three of the principles of stratigraphy
nicolas steno
a break in the rock record produced by erosion and/or nondeposition of rock units
* Represents “lost time”; a geologic mystery
- may disturb stratification of rocks
unconformities
types of unconformities
angular unconformity, disconformity, nonconformity, paraconformity
unconformity
rocks get tilted by deformation and are overlain by flat-lying rocks
- tilting, folding, faulting - rocks change the angle
angular unconformity
unconformity
- strata on either side of the
unconformity are parallel but irregular due to
erosion - somehow it conforms
- eroded layer in the middle, may look continuous
disconformity
unconformity
- metamorphic or igneous rocks
come in contact with sedimentary strata to folding or
uplifting - not at all
nonconformity
unconformity
- overlying rocks are parallel and continuous to the previous one
- as if almost
- multiple similar layers - hard to tell the boundary of each time
paraconformity
Numerical age; estimated age; Quantitative
* makes use of Radiometric Dating- Half life of Radioactive Isotopes
absolute dating
calculates an age in years for geologic materials by measuring the presence of a short-life radioactive element
- The ratio of radioactive isotopes and the daughter
is taken to estimate the age of materials
radiometric dating
the time required for half of the atoms
in a sample to decay to daughter atoms
- rate of decay
half-life
The ratio of carbon-12 to carbon-14 is the ______ in all
living things.
* At the moment of death, the amount of________
begins to decrease because it is unstable, while the
amount of ___________ remains constant in the
sample
same; carbon-14;carbon 12
carbon 14 decays into
nitrogen-14
half life of carbon-14
5730 years
who proposed the innovative method for dating organic materials by measuring their content of carbon-14
willard libby
time limit of c-14 dating
approx. 50000 years
is c-14 accurate
it may not be someday as fossils disturb this by carbon emmissions
limitations of radiometric dating
isotopes may not be found in some rocks/fossils
daughter and half life of al-26
mg-26; 740 thousand
daughter and half life of I-129
xe-129; 17 million
daughter and half life of U-235
(lead) Pb-207; 704 million
daughter and half life of K-40
Ar-40; 1.3 b
daughter and half life of U-238
Pb-206; 4.5 b
daughter and half life of Th-232
Pb-208; 14 b
daughter and half life of (rubidium) rb-87
sr-87; 49 b
decay of uranium and thorium isotopes, aside from lead, also yields
helium
decay of uranium and thorium isotopes, aside from lead, also yields
helium
