Geology Flashcards
Law of superposition
The Law of Superposition states that beds of rock on top are usually younger than those deposited below.
Absolute dating def
Absolute dating: Absolute dating is a method used to determine the specific age of a rock or fossil in years, qualitative
How is absolute dating usually carried out
through the use of radiometric techniques that measure the decay of radioactive isotopes.
Relative dating def
relative dating is a method used to determine the age of rocks or fossils by comparing their positions in relation to other rocks or fossils, quantitative
The law of uniformitarianism
the earth has always changed in uniform ways and that the present is key to the past
Weathering of rocks must take place
On the surface
Sedimentary rocks were likely formed
in water
Law of original horizontality
Layers of sedimentary rock are originally deposited flat
Law of crosscutting relationships
The cut rock layers are older than the rock that cuts across them.
Law of lateral continuity
Rock layers extend laterally until they encounter other solid bodies that block their deposition or acted upon after deposition
unconformity
a break in time in an otherwise continuous rock record
Fold
undulation or waves in stratified rock, caused by pressure that uplifts
Fault
a fracture or discontinuity in the Earth’s crust where rocks on either side have moved relative to each other,
Index fossil
a fossil that is useful for dating and correlating the strata in which it is found.
A useful index fossil
easily recognizable, abundant, and have a wide geographic distribution and a short range through time.
Radioactive isotopes are
isotopes that are unstable and break down into other isotopes by a process called radioactive decay.
The radioactive isotope is called
the parent isotope,
and the stable isotope formed by its breakdown is called
the daughter isotope.
Half-life is
time needed for half of a sample of a radioactive element to undergo radioactive decay and form daughter isotopes.
Once a plant or animal dies
No carbon 14 can enter
Who proposed the theory of Pangaea
Alfred Wegener
Continental drift
Over millions of years, the continents slowly drift into their present-day positions.
tectonic plates def
gigantic pieces of the Earth’s crust and uppermost mantle
Contiental drift theory how
The Jigsaw Fit
Fossil correlation
Rock and Mountain correlation
Paleo climate correlation
What is missing from his theory
There is no mechanism for how the continents could shift
How was contiental drift mechanism found
Hess’ theory of seafloor spreading, lava from the earth’s mantle pushes the oceanic crust apart
Mid Ocean Ridges
Underground mountains formed by the solidification of underwater lava
Ocean trenches
when one plate goes under the other
Age of seafloor
Further rocks are from ridges the older they are
Convection Current (in the mantle)
Circulation patterns that occur as dense rocks sink and less dense rocks rise
Tectonic plates move
relative to each other
Oceanic crust
Crust that forms the Oceanic basin
More dense than continental crust
Gets recycled through subduction, younger
Continental crust
Crust that forms the contients
Less dense than oceanic crust
Doesn’t get recyled, older
The rocks formed from the mid ocean ridge (magnetic)
preserve the magnetic polarity, creating a rock record of it
Plate Boundaries are
The places where tectonic plates meet
Transformative/conservative boundaries are characterised by
the parralell sliding of plates, they move slowly and then ‘slip’ (san andreas)
Divergent boundaries are characterised by
The Spreading of plates moving away from each other, creates mid ocean ridges (iceland)
Convergent boundaries are characterised by
the collision of plates, one will slip beneath the other, creating a trench or subduction zone, or a mountain (himalaya mountains)
In convergent boundaries, which is more likely to subduct
The older, as it is most likely more dense
Why do tectonic plates move
- Friction between the convection cell and the tectonic plates is strong enough to move it
2
Why is oceanic crust thinner
it is recycled more and doesn’t have chance for a lot of sediment to deposit on it.
