Alfred Wegener-- theory
a German scientist who proposed a hypothesis stating the continents once formed a single landmass, called a supercontinent, then broke up and drifted to their present locations, in 1912; this hypothesis is now called continental drift and explains why the
Continental Drift
hypothesis stating that the continents once formed a single landmass, called a supercontinent, then broke up and drifted to their present locations; explains why the continents seem to fit together like the pieces of a jigsaw puzzle
Wegener-- More evidence
also found other evidence to support continental drift; said that if the continents were once joined, fossils of the same plants and animals should be found in areas that were once connected; fossils of the Mesosaurus were found in both South America and
Mesosaurus
a freshwater reptile; fossils found in both South America and western Africa
Glossopteris
ancient fern; fossils were found on several southern continents
Wegener-- impact of theory
despite several forms of evidence supporting the hypothesis of continental drift, Wegener's ideas were strongly opposed by other scientists; they rejected his explanation of how the continents moved as he stated teh continents plowed through the rock of t
Mid-ocean ridges
chains of submerged mountains at the bottom of the oceans; sediment is thinner closer to the ridge; ocean floor is very young (radiometric dating showed no rocks older than 200 million years)
Harry Hess
a geologist; suggested a new hypothesis stating the valley at the center of the ridge was a crack, or rift, in Earth's crust;; at the rift, magma comes up from deep inside of Earth; this process is known as sea-floor spreading
Rift
crack
Sea-floor spreading
the process where new oceanic lithosphere forms as magma rises to Earth's surface and solidifies at the mid-ocean ridge
Paleomagnetism
the study of the magnetic properties of rock; as magma solidifies to form rock, iron-rich minerals align with the Earth's magnetic field
Normal polarity
when the magnetic field points to the geographic north
Reverse polarity
when the magnetic field points to the geographic south
Earth's crust
the thin, rocky outermost portion of the Earth; classified into two types: oceanic and continental
Oceanic Crust
about 7 km. thick; average density of 3.0 g/cm^3; made or mainly basalt; more dense than continental crust
Continental Crust
about 40 km. thick; average density of 2.7 g/cm^3; made of mainly granite
Andrija Mohorovici
a Croatian scientist; discovered a boundary seperating the Earth's crust from the mantle; did so by studying seismic waves and found their velocity increased dramatically about 50 km. below the surface
Mohorovicic Discontinuity "Moho
the boundary seperating the crust from the mantle; named after Andrija Mohorovici, who discovered it
Plate tectonics
the theory explaining how the continents move and the study of the formation of features in Earth's crust
Lithosphere
a layer of Earth formed by Earth's crust and the rigid, upper part of the mantle; forms the outer shell of the Earth
Tectonic plates
plates that move on part of the mantle known as the asthenosphere
Asthenosphere
a plastic, putty-like layer of rock below the lithosphere
Earth's Mantle
contains the majority of Earth's mass and volume; the process of convection occurs within this layer; 2 different parts-- upper mantle: lithosphere and asthenosphere and the lower mantle
Earth's Core
the inner-most sphere of the Earth; Iron and Nickel composition; average density of 13 g/cm^3; divided into 2 distinct parts: outer core and inner core
Outer Core
liquid layer; flowing metallic Iron generates Earth's magnetic field
Inner Core
Solid, densest part of Earth; despite its high temperatures, the material is compressed into a solic due to intense pressure
Pacific Ring of Fire
a zone of several earthquakes and active volcanoes; indicates the Pacific Ocean is surrounded by plate boundaries
Divergent Plate Boundary
a boundary occuring when two tectonic plates seperate, or move away from each other; new sea floor forms at divergent boundaries; most common--> mid-ocean ridges
Convergent Plate Boundary
a boundary occuring when two tectonic plates, collide, or come together; the region along a plate boundary where one plate moves under another plate is called a subduction zone
Subduction Zone
the region along a plate boundary where one plate moves under another plate
Transform Plate Boundary
a boundary occuring when two tectonic plates slide past each other horizontally; example: San Andreas Fault, CA
Convection
the mantle is the driving force behind plate movement
Ridge push
pushes the rest of the plate away from the ridge; exerted when cooling rock coming up from mid-ocean ridges slide down the slop of the ridge
Slab pull
where the lithosphere is dense enough, it begins to subduct into the asthenosphere; as the leading edge of the plate sinks, this force pulls the rest of the plate along behind it
Rifting
the process by which a continent breaks apart resulting in new smaller continents
Terrane
a piece of lithosphere that has a unique geologic history and may be part of a larger piece of lithosphere, such as a continent
supercontinent cycle
the process by which supercontinents form adn break apart over millions of years; the collision of plate boundaries along with the formation of rifts creates this movement of the continents across the globe
Rodinia
supercontinent existing about 1 BYA, meaning "motherland"; all of the landmases were gathered south of the equator
Pangaea
supercontinent existing about 300 MYA, meaning "all Earth"; continents rejoined to form this supercontinent after being seperated as they are today in about 450 MYA; as a result of continental collisions during Pangaea, certain mountain ranges formed, inc
Laurasia
a northern piece of land forming when Pangaea began to split apart around 200 MYA
Gondwanaland
a southern piece of land forming when Pangaea began to split apart around 200 MYA
Pangaea Ultima
new supercontinent that will form in about 250 million years; it is believed if plate movements continue at current rates, n 150 million years, Africa will colide with Eurasia and the Mediterranean Sea will close; new subduction zones will form, closing o