Plate Tectonics Flashcards
the principle of superposition
-the top is more recent than the bottom
- but you cannot tell how long it took to accumulate (cannot tell temporally)
- sedimentary rock record shows a succession of fossils through time
stratigraphic ranges
- the overlapping range zones of two or more fossils with different geologic ranges
- intervals of geologic time
index fossils
-best fossils for correlation and relative dating
- short stratigraphic range
- abundant
- well-preserved
- wide geographic distribution
half life
useful in dating rock
-have to strategically choose an isotope to measure
ZrSiO4
- zircon
- small, hard and resistant to melting
Evidence of Pangea
-rocks and fossils reflecting similar environments were found on continents that are far apart & at different latitudes
“continental drift”
- Wegener’s proposal that continents plowed through oceanic crust
- was not accepted by other geologists
- has been subsumed by the theory of plate tectonics
convection currents
- proposed as the driving mechanism for Plate Tectonics
- beneath the crust, within the upper mantle
- many geoscientists did not accept bc no direct evidence
evidence of tectonic plate shift
- magnetite grains (igneous rocks) are natural compasses that point towards the north poles
- North Poles appear to have changed through time
why is Earth’s igneous seafloor “young?”
-crust is constantly shifting driven by convection in the mantle because the mantle is rocky but hot and in motion by the radioactive decay of unstable isotopes from many elements
Mid-Ocean Ridge Divergent Boundary
- the mantle is unusually hot under the mid-ocean ridge
- small amounts of magma rise to the seafloor and add igneous crust
evidence for the edge of tectonic plates
-pattern of seismic activity (earthquakes) and volcanism
