geologic time (LEC 6) Flashcards
name the two types of geological dating
numeric dating and relative dating
what is numeric dating vs relative dating
*numeric date is the actual number of years that have passed since an event occurred.
*relative dating means that rocks are placed in their proper sequence of formation (doesn’t give us the age of rocks, only their order)
what is the law of superposition
in an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below it
what is the principle of lateral continuity
sedimentary beds originate as continuous layers in all
directions
what is the principle of cross-cutting relationships
geologic features that cut across rocks form after the rocks they cut through
what is the principle of inclusions
inclusions are fragments of one rock unit that have been enclosed in another rock
an _________ is a break or gap in the rock record caused by uplift, erosion, subsidence and new sedimentation
unconformity
when there is no break in the rock record, the rocks are considered __________
conformable
an English engineer (late 1700s), noted that sedimentary strata in widely separated areas could be identified and correlated by their distinctive fossil content. whats his name
William Smith
what is fossil assemblage
a group of fossils that can be used to date rocks more precisely than a single fossil
what are index fossils
their presence allows us to match that rock to a specific
period
what is correlation of rock layers
rocks of the same age in different areas of the earth can be matched up which allows scientists to develop a geologic time scale that applies to the entire earth
the number of protons in the nucleus is the _______ _________
atomic number
the number of neutrons can vary for the same element. variants of such an element are called __________
isotopes
Unstable nuclei spontaneously break apart and emit energy in a process called _________________ ________
nuclear or radioactive decay.
