Chapter 10 Flashcards
Cambrian explosion
The remarkable diversification of life, indicated by the fossil record, that occurred at the beginning of the period of the same name
Carbon dating
A radiometric dating process that can tell us the age of organic material containing carbon originally extracted from the atmosphere
Contact
The boundary surface between two rock bodies (as between two stratigraphic formations, between an igneous intrusion and adjacent rock, between two igneous rock bodies, or between rocks juxtaposed by a fault)
correlation
The process of defining the age relations between the strata at one locality and the strata at another locality (even across seas!)
cross-cutting relations
A means of determining the relative age of rock by looking at which rock or structure cuts another. the feature that has been cut is older
daughter isotope
The product isotopes of radioactive decay
eon
The largest subdivision of geologic time, breaks all time into 4 parts
Epoch
An interval of geologic time representing the largest subdivision of a period
era
An interval of geologic time representing the largest subdivision of the Phanerozoic Eon (only this Eon is subdivided, and it is divided into 3)
fossil succession
The principle that the assemblage of fossil species in a given sequence of sedimentary strata differs from that found in older sequences or in younger sequences. a given species appears at a certain level and then disappears (goes extinct) at a higher level
4.57 billion years old
The age of the earth according to isotopic dating.
Name two alternative methods for geological dating.
Counting tree rings or seasonal layers in glaciers.
Disconformity
layers of sediment accumulate, sea level drops and an erosion surface forms, sea level rises and new sedimentary layers accumulate (looks like the tilt of a beach in diagrams
Angular Unconformity
This type of UNCONFORMITY has rock layers that are tilted, and younger sediment layers are deposited horizontally on top of the eroded and tilted layers.
Non-Conformity
Igneous or metamorphic rock that has been eroded and included in the rock above
marker bed
An easily identified geologic layer whose age has been independently confirmed at numerous locations and whose presence can therefore be used to date archaeological and geological sediments.
index fossil
a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found
geologic column
an ideal sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest, may also be composed for a single region
geologic map
Shows the surface geology of the mapped Includes rock types, their ages, and location of faults
geologic time
A record of the geologic events and life forms in Earth’s history, divided into 4 eons OR 4 eras, includes scale
half-life
The time it takes for half of a group of a radioactive element’s isotopes to decay
isotope
Different versions of a given element that have the same atomic number but different atomic weights, aka have more or less neutrons
isotopic dating
The science of dating geologic events in years by measuring the ratio of parent radioactive isotopes to daughter product isotopes
numerical age
The age of a rock or structure as specified in years. referred to as ‘absolute age’ in older literature. Absolute was abandoned because in reality, this is still a guess. May be done through radiometric, carbon, or isotopic dating (all the same idea).
original horizontality
The principle that sediments are deposited in nearly horizontal layers (1st principle of relative dating)
parent isotope
A radioactive isotope that undergoes decay
geochronology
study of the ages of geologic events
fossil assemblage
a group of fossil species found in a specific sequence of sedimentary rock
closure temperature
One of the problems with radiometric dating, radioactive material must reach a certain temperature before it begins to “set it’s timer”. Hence, no rocks date back to the Hadean eon (never reached this temp).
uniformitarianism
The principle that the same physical processes observed today are responsible for the formation of ancient geologic features. put concisely, ‘the present is the key to the past’. Hutton.
unconformity
A boundary between two different rock sequences representing an interval of time during which new strata were not deposited and/or were eroded
superposition
The principle that younger layers of sediment are deposited on older layers of sediment. thus, in a sequence of strata, the oldest layer is at the base
stratigraphic formation
A recognizable layer of a specific sedimentary rock type or set of rock types, deposited during a certain time interval, that can be traced over a broad region. Places two now separate land masses as being connected at a certain time.
stratigraphic column
A cross-section diagram of a sequence of strata summarizing information about the sequence in a given region
relative age
The age of one geologic feature with respect to another, eg feature A is older than feature B
period
An interval of geologic time representing a subdivision of a geologic era–these names were given at different times and are not all the same length and do not follow a pattern for their names.
Precambrian
The interval of geologic time (known as an era, divided into 3 eons) between Earth’s formation about 4.57 Ga and the beginning of the Phanerozoic Eon 542 Ma
radioactive decay
The process by which a radioactive atom undergoes fission aka releases particles thereby transforming into a new element
