Geological Time
No description yet. This curated deck is ready for daily study.
Card preview (24)
What steps are taken to determine the age of the MIssissippi River Delta?
1) calculate volume of sediment that comes out (km cubed) 2) calculate average annual discharge (km cubed per year) 3) divide volume of sediment by average annual discharge - gives time it took for all the sediment to get there
What sort of measurement is relative dating?
qualitative
How does relative dating work, in basic terms?
compare two features and ask if one is older, younger, or the same age as any other geological feature
What are the main rules of relative geological time?
superposition, cross-cutting relationships, unconformity surfaces, and flaural/faunal succession (and original horizontality, lateral continuity, baked contacts, inclusions)
What is uniformitarianism?
principle that the physical processes we observe today also operated in the past at around the same rates and are responsible for the formation of geological features we see today
What is the principle of superposition?
layered rocks laid down one on top of another; older below younger - things are deposited in vertical sequence
What is the principle of cross-cutting relationships?
the geological feature that is cut is older than the feature that cut it
What do inclusions indicate about relative age?
the inclusion must be older than the geological feature that included it (it had to exist to be included)
What do instursive contacts indicate about relative age?
instrusion is younger than host rock (cross-cutting)
What do faults/folds indicate about relative age?
geological feature must be older than fault/fold - was originally deposited straight and continuously, so if now fractured/folded, fracturing/folding happened after
What is an example of an inclusion?
xenolith
What is an unconformity surface?
surface representing a period of nondeposition and possible erosion that represents a gap in the geologic record
Why do unconformity surfaces represent a gap in time?
because the sequence of strata have a relative time significance
What is a hiatus?
a gap in time
What are angular unconformities?
unconformity surface in which rocks below it were tilted/folded before development of unconformity; AU cuts across underlying layers, so orientations of layers above and below are different (tilted rock underneath; flat lying rock on top)
What do angular unconformity imply?
1) deposition of underlying rock 2) deformation of underlying rock 3) uplift and erosion ot flatten top 4) deposition of flat-lying sediment on top of the unconformity surface
What are the principles of faunal and floral sucession?
fossils vary with time; thus fossils used in rock layers of different age will be different
What are some indications of unconformities?
difference in orientation; differences in dip; gap in fossil succession; pebbly layer of debris (from erosion)
How can faunal/floral sucession be sused to establish relative time scales over broad areas?
a particular group of fossil species can only be found in a limited interval of strata; when one species disappears at end of a strata, it never reappears; therefore can match up fossils over large areas
What are index fossils?
fossils of species that only existed for a short interval of geological time and are thus diagnostic of a particular time interval (like old cell phones = old movies)
What are the characteristics of index fossils?
easily identified; only lived for a very short time; widely-distributed geographically; widely-distributed environmentally; abundant
Why was the geological time scale developed?
to correlate and standardize everyonne’s findings
What are the charactersitics of the geological time scale?
arbitrary, subjective, and utilitarian
What are the general divisions of the geological time scale, from most broad to smallest?
eon, era, period, (epoch)