Week 1 Test Flashcards
How much of a radioactive parent isotope will remain after 3 half-lives have passed?
One eighth
Accurate radiometric daring is possible only if a rock contains a measurable amount of _______
Both parent and daughter atoms
If an igneous dike cuts across a sequence of sedimentary beds, _____
The beds must be colder
If the lithology and fossil content of two bodies of rock on opposite sides of a canyon are identical, then these remaining outcrops were likely physically connected at one time and formed part of an extensive, sheet-like layer of rock. This idea summarises the principle of _______
Original continuity
Based on the figure, what is the age of layer 7 relative to layer 3? [layer 7 is higher than layer 3]
layer 7 is younger than layer 3
Numerical ages for boundaries between time units on the geologic time scale primarily resulted from the study of ________, in conjunction with relative age data.
Radiometric dating of igneous rocks
In the area immediately surrounding an igneous intrusions, a host limestone is locally metamorphosed to produce marble. Which is older?
The limestone is older than the marble
Which method of correlation is most reliable for determining age equivalence amount bodies of rock that are physically separated by vast distances?
Fossil correlation
If horizontal sedimentary strata overlie tiled strata (and no fault is present), the surface between the horizontal and tilted strata must be an ____
Angular unconformity
Within the worlds sedimentary rocks, fossils ____
Occur in an ordered sequence
Which statement about #3 is correct?
It and #2 once formed a continuous unconformity
What is always the same for different isotopes of a single element?
Atomic number
Which of the following geologic principles is not the result of gravity?
Cross cutting relationships
Radiometric dates applied to sedimentary rocks produce ages that are _____
Too old - predate sedimentary deposition
Balsamic coasts within a conglomerate have been radiometric ally dated to 50 mill yrs ago. Is this a reliable age?
No, likely too old
Summarise the development of the geologic time scale?
Relative ages for sedimentary strata were known well before accurate numerical dates for these rocks could be provided
If a basalt body cuts across a daily, what are relative ages of basalt and the fault?
The fault must be older, according to the principle of cross cutting relationships
As understood by modern geologists, the principle of uniformitarianism implies that ____
Physical processes observed today (e.g. erosion and volcanic eruption) have been active in the past and are preserved in the rock record
How is the half life of a radioactive parent isotope defined?
The time for half of the parent isotope to decay to daughter isotope
Buried erosions surfaces between parallel sedimentary strata are termed ___
Disconformities
If the relative ages of two formations are known, what else can be inferred?
Their relative position in a sequence of the rock layers
Can the age of the earth be reliably estimated from sediment thicknesses?
No - much of earths history is represented by unconformities between strata rather than the strata themselves
Two atoms of a single element that differ in number of neutrons are said to represent two distinct _____ of that element
Isotopes
A radiometric age for a mineral crystal within an igneous rock measured the amount of time that has passed since the _____
Temperature of the crystal became equal to the closure temperature for the mineral
