PLATE TECTONICS

Early Thoughts on PT

Scientists recognized that the continents appeared to fit together, most notably Africa and South America

Also fossils from the same land organisms were found on continents separated by oceans

Early Theory: Continental Drift

Scientists developed the theory of continental drift which stated that the continents had ‘drifted away’ from each other over time

Naval Technology

Sonar and the mapping of the seafloor lead to the discover of lithospheric plate boundaries at mid-ocean ridges

This led to the Theory of Plate Tectonics

-Theory that describes the formation, movement, and interactions of

lithospheric plates

-These plates carry the continents and ocean basins with them

Evidence for Plate Tectonics

-Seismologists plotting the location of recent

earthquake activity noticed that the earthquakes were in concentrated belts on Earth’s surface

-These belts of activity actually outline the plates

Volcanic Activity

-Similarly, volcanoes were located in concentrated belts as well

-Also on plate boundaries where high heat flow occurs

Age of Rocks

-Samples show newer rocks form closest to

divergent boundaries such as the mid-Atlantic ridge

-Older rocks are pushed away but match equidistant on either side

Magnetic Polarity

-Some minerals have magnetic properties

-When magma cools, the rocks record the polarity in the rock

-Sometimes polarity reverses and is recorded in the rock

-Rocks equidistant from divergent boundaries are the same polarity

Tectonic Plates

How do the plates interact?

-Plate motions vary and interactions at boundaries vary

-There are 3 types of plate boundaries:

-Divergent

-Convergent

-Transform

Divergent Boundaries

-Boundary where two plates are moving apart

-Prefix di- meaning apart (think division)

-Most divergent boundaries are on the ocean floor

-Rift valleys form along divergent boundaries on continents

Divergent Boundaries

-New crust is being formed as plates slide away from each

other and magma rises to the surface

-This lava cools and solidifies becoming new crust

-Expect very fine-grained igneous rocks due to the fast cooling rate

Convergent Boundaries

-Boundary where two plates are moving towards each other

-Prefix con- meaning together (think contract, deal that brings two people together)

-2 types

-Subduction boundaries

-Collision boundaries

Subduction Boundaries

-A subduction boundary exists where an oceanic plate plunges below another

-A deep-sea trench is formed

-Ocean-Ocean: chain of volcanic islands is formed

-Ocean-Continent: inland mountain chain and volcanoes formed

Subduction Boundaries

-The more dense oceanic plate (basaltic rock) will subduct

(slide below) the less dense, yet thicker continental plate (granitic rock)

-In some cases, the oceanic crust will subduct below other oceanic crust

Collision Boundaries

-If two plates carrying continents collide, they may make a larger landmass

-Form a mountain range

-Example: Himalayas (Asia and India)

Transform Boundaries

-Boundary between two plates sliding past each other

-Example: San Andreas Fault

What causes plate movement?

-Mantle convection: the idea that rising, less dense material pushes earth’s plates

Formations at Plate Boundaries

-Divergent: Ridges and rift valleys; new crust is being formed

Convergent/Subduction:

-Ocean/Ocean Volcanic island arc as subducting plate melts

-Ocean/Continent Volcanic mountain ranges

Unique Formations

-Hotspots: Caused by plumes of hot material that punch through the Earth’s crust as a volcanic eruption

-Example: Hawaii

Plate Movements Over Time

-Influenced evolution of species by changing

climate as continents drifted to different latitudes

-Species needed to evolve to maintain body temperature/moisture

-Landscapes and geography changed as well as a result of tectonic features and erosion/deposition