Continental Drift Flashcards
who first purposed continental drift?
alfred wegener
what was some of things wegener observed that made him think that the continents had drifted?
- africa and south america fit together well
-evidence of glacation in tropics
-evidence of desert sands in temperate regions
-evidence of tropical plants in antarctic
-fossils of animals/plants in geographically separated regions
what is continental drift?
continents have moved over time
what was the key characteristic of solid materials that made drift possible?
solid materials could flow like putty (matter of time and scale)
Palaeomagnetism (def.)
the study of the Earth’s magnetic field preserved in rocks
how does paleomagnetism indicate that continents have drifted over time?
-basalts & gabbros have ferromagnesian minerals that are wealky magnetic at surface (cool) temperaturs and not magnetic at hot temp. As magma cools below curie point , the Fe minearls align along magnetic field (they retain paleomagnetism unless heated)
-minerals align with magnetic field which run N-S, and dip with latitude so you can determine the location of rock when it was magnetized (in respect to magnetic north)
what is polar wander curve and connection to the continenetial drift?
rocks on different ages on single continent look like they are pointing to different magnetic north; looks like pole wander with time but actually continents moved while pole remained static
paleomagnetism helped us determine the existence of which supercontinent?
pangaea around 200 millions year ago
pangaea existed when? started to break when? the continents we know now formed when?
-triassic (early)
-jurassic
-creataceous
gondwana part of pangaea is now what?
africa, south america, india, australia
laurasia part of pangaea is now what?
north ameria, europe, asia
50 million years in the future, what the main changes to the continenets we expect?
africa and europe collide
north and south america come closer
what is magnetic reversal? what is the effect on rocks?
-N/S magnetic pole swap
- rocks crystallizing when magnetic orientation is the same as today = normally magnetized
-rocks crystallizing when magnetic orientation is the opposite as today = reversely magnetized
what is geomagnetic excursions?
like magnetic reversal but not permanent change of large scale field ; usually short-lived of change with variation of up to 45 degrees
geomagnetic reversal and excursions pose a risk to the earth in what way?
magnetic field helps protect us from radiation