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57 terms

Geology- ch8

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james hutton
who is regarded as the father of geology
charles lyell
who wrote the book Principles of Geology
uiformitarianism
james huttons concept that geologic operating at preset are the same processes that operated in the past eventually became known as teh principle of ______________ (the present is the key to the past)
actualism
a principle that the same processes and natural laws operated in the past are those we can actually observe or infer from observations as operating in the present
numerical
dating based on radioactivity allows us to determine a rocks ___________ age (age given in units of time)
absolute
numerical age is also known as _________age
relative
_____________ time is the sequence in which events took place , rather than the number of years involved (geologist are more concerned with this number)
contacts
the surfaces seperating 2 different rock types or rocks of different ages (used to decipher geological history)
formation
bodies of rock of considerable thickness with recognizable bodies characteristics that make each distiguishable from adjacent rock units (named after geographic features)
stratigraphy
the subdiscipline in geography that uses interrelationships between layered rock or sediment to interpret the history of an area
original horizantally
the principle of ____________________ states that beds of sediment deposited in water formed as horizantal or nearly horizantal layers
superposition
the principle of _______________ states that within a sequence of undistrubed sedimentary or volcanic rock, the layers get younger going from bottom to top
lateral continuity
the principle of _______________________ states that an original sedimentary layer extends laterally until it taper or thins at its edges
cross cutting relationships
the principle of ___________________________ states that a disrupted pattern is older than the cause of the dispruption
intrusive contact
rock which intruded after orginal rock layer was formed
unconformities
contacts representing buried erosion surfaces-a surface or contact that represents a gap in the geoligic record with the rock layer above the contact being considerably younger than the rock beneath
tectonic forces
what can cause the overturning or disruption of beds so much that the principle of superposition cannot be used
contact metamorphosed
the tilted layers immediately adjacent to granite bodies are ____________________ a result of intrusion of hot granite magma
inclusion
the principle of _______________ states that fragments included in a host rock are OLDER than the host rock
disconformity
in a ________________ the contact representing missing rock strata seperates beds that are parallell to one another (probably the older rock eroded away
angular uncomformity
an __________________ is a contact in which younger strata overlie an erosion surface on tilted or folded layered rock (implies- deposition, lithofication, uplift, erosion)
noncomformity
a _____________ is a contact in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimenary or volcanic rock (generally indicates deep or long erosion before subsequent burial)
correlation
__________________usually means determining time equivalency of rock units (within a region, continent)
physical continuity
this type of correlation traces physically the course a rock unit
unusual
correlation by rock type is more reliable if a very ____________sequece of rock or involved
continental drift
what theory uses correlation of rock type as its proof
key bed
a very distinctive layer can be used to correlate rocks over great distances (volcanic ash)
fossils
these are common in sedimentary rock and their presence is important for correlation
faunal succession
the discovery of william smith who realized that fossil species succeed one another through the layers in a predictable order
paleontologist
______________ speciallize in the study of fossils
index
this type of fossil is from a short lived - geographically widespread species
fossil assemblage
several different fossil species in na rock layer (more useful than a single fossil)
standard geologic time scale
a world wide relative time scale - based on fossil assemblage
three
how many eras are in the geologic time scale
paleozoic
which era in the standard geologic time scale means "old life"
middle life
the mesozoic era means __________________ this was the time of the dinosaurs
holocene
which ephoch in time are we in
paleozoic
all the horizantal rock in the grand canyon are ________________
sedimentary deposits
layers of _____________________ can be counted to determine how long lakes existed
gneiss
the oldest rock found on earth is a ______________ from northwestern canada (dated 4.03 billion years old)
zircon crystal
the oldest mineral is a ____________ from australia which is 4.4 billion years old
ratio
if we can determine the ________ of a particular radioactive element and its decay products in a mieral we can calculate how long ago that mineral crystallized
isotopic dating
determinig the age of a rock through its radioactive elements
isotope
atoms of a given element that have different numbers of neutrons but the same number of protons
radioactive decay
________________ is the spontanious nuclear change of isotopes with unstable nuclei
energy
what is produced with radioactive decay
geiger counter
what measures the energy in radioactive decay
alpha emission
a radioactive change where the atomic number is reduced by 2 and the atomic mass is reduced by 4 (ex uranium(238) to thorium)
beta emission
a radioactive change which involves the release of an electron from the nucleus (ex. Th (234)to Pa(234))
electron capture
a radioactive change whereby a proton in the nucleus captures an orbitting electron- the proton becomes a neutron
(ex Potassuium becomes Argon)
half life
the rate of proportional decay - the time it takes for a given amount of a radioactive isotope to be reduced by one-half
1.3
how many billions of years is potassiums (K)'s half life
5730
how may years is carbon 14's half life
40,000
because of the short half life of C14 it is only accurate back to about _______________
igneous
what type of rocks are best for dating
sedimentary
what type of rocks are difficult to date reliably
kelvin
who, in 1866, calculated backwards that the entire earth must have been molton 20-40 million years ago (age found wrong by radioactivity and heat energy)