TIME AND TECTONICS IN GEOSPHERE Flashcards
when was the geologic time scale developed?
1800
when was radioactivity discovered and its definition
- 20th century
- measurment of geologic time
description and principle
stratigraphy
- relative age dating for sedimentary rock
- 18th century basic principles from observing layers of sedimentary rock
1. correlation
2. order of strata
3. cross cutting
correlation by lithology
- comparing sucessions of layers in different places
description and example, a date
correlation by fossils
- correlating strata based on fossils
- its characteristics are adundancy, a wide distribution, marine and rapid evolution
*abundant in paleozoic
description and example
cross cutting relationships
- events that modify rocks after deposition
- show relative age of features
- examples are uncomformities, faults, igneous intrusions
dykes and inrusions are..
are younger than the host rocks
precambrian division of eons
protozeroic, archean, hadean
how is the phanerzoic eon divided
- fossil investigations
- superposition
- cross cutting
order of strata
- sedimentary rocks thatrecord environmental change
the sucession of sedimentary layers is illustrated in..
stratigraphic columns
absolute time method
isotopic dating
isotopic dating -neurons
- neurons play a role in binding the nuckeus together
- the number of neutrons can vary- it defines
radioactive decay
*unstable isotopes decay to create stable isotopes
* so nucleus breaks apart and undergoes decay, and creates a new element randomly
* the rate is predictable
* used for measurement of geologic time
radioactive decy-
half life
the time for half the atoms of an isotope to decay
* after 2 half lives, a quarter of atoms are left
radioactive decay-
daughter atoms
- the new element of the decay
requirements of age determination
- half life or decay constant
- final amount of parent isotope
- og amount of parent isotope or final amount of daughter isotope
when did the great oxygenation event occur
2.45 ga - 2.2 ga
when was the emergence of photosynthesis
1.25 ga
oceanic crust make up
- mafic igneous rock
- basalt
continental crust
- igneous, sedimentary, metamorphic
- intermediate - felsic composition
hypotheis date
contental drift date
1914
gravity and the asthenosphere
- stronger attraction to denser rocks close to the surface
- measure of gravity is all objects attract each other according to mass
*
what started the theory
theory of isotasy
- mtns are underlain by lighter rocks / asthenosphere
asthenosphere
- The layer of the mantle lying beneath the lithosphere and capable of plastic flow
- can allow plate movement to occur
lithosphere
- division of plates above the asthenosphere\
- undergoes vertical isostatic rebound after ice melts
dipole field
The magnetic field produced by a magnetized body with north and south poles on opposite sides
magnetism
- the magnetic core of earth suggests it is circulating liquid iron
*
declination
- The direction relative to the north of Earth’s magnetic field.
- indicates direction to the pole
inclination
The steepness of Earth’s magnetic field/ of the declination
* indicates distance from the pole
paleomagnetism
- The study of preserved magnetism in ancient rocks
- when magnetite cools it is magnetized by the surrounding megnetic by the earths field
remnant magnetism
- magnetite rocks form and make a record of the earth magnetic field as it existed at the time of their formation, so
- RM determines the ancient location of the N or S pole relative to rocks as currently found
MAGNETIC REVERSALS
reversal of N and S poles
recorded by remnant magnetism
MAGNETIC ANOMOLY
field slightly stronger or weaker than normal
* result from remnant magnetism acquired during spreading of ocean floor while magnetic reversals occured
* determines age of ocean floor
