Transcript plate tectonics

Core
Mantle
Lithosphere
• Inner Core (solid Fe and Ni)
• Outer Core (liquid Fe and Ni)
• Lower Mantle (solid)
• Asthenosphere (hot, taffy-like part; the “plates”
move on it when driven by convection currents
• Upper Mantle (solid)
• CRUST: 2 types: Oceanic (more dense) or
Continental (less dense)
Continental Crust
Oceanic Crust
Rock Type
Granite
Basalt
Color
Light
Dark
Composition
High Si, Low Fe
Low Si, High Fe
Density
Low
High
Average Thickness
40 km, avg.
6-7 km, avg.
Depth
(general)
Floats higher in the
mantle
Floats lower in the
mantle – form basins
that fill with water
 Hypothesis proposed by Alfred Wegner, a German
Scientist, in 1912
 A theory that at one time all the continents were
joined as one supercontinent called Pangaea (Greek
word meaning “all the earth”), and over time have
been drifting apart. Continental Drift gave an
explanation to finding similar organisms, rock types
and past glacial activity on several different continents
– in Wegener’s time and today.
 Wegener thought the continents were pushing
through a stationary ocean floor but he couldn’t
prove it, so many people rejected his theory.
THEN
NOW
 http://www.scotese.com/pangeanim.htm
 In the early 1900s most people, including
scientists, believed that the ocean floor was flat.
Advances in technology in the 1940s and 1950s
proved this theory to be wrong.
 Sonar, a type of echo sounding device that uses
sound waves to measure water depth, is one
advance that allowed scientists to study the ocean
floor in detail.
 Another advance was the magnetometer, a device
that can detect small changes in magnetic fields.
This is a great tool because the ocean crust has a
lot of iron in it.
 Maps were made using sonar and magnetometer
data and showed scientists that the ocean floor had
different landforms like they saw on Earth’s surface.
 Topographic maps were made from sonar and
magnetometer data that helped to discover vast,
underwater mountain chains called mid-ocean
ridges, and underwater ditches called deep-sea
trenches.
 The longest mountain chain in the world is the
Mid-Atlantic Ridge, found in the Atlantic Ocean.
 The deepest trench is the Marianas Trench, found
in the Pacific Ocean .
 Scientists found that rock samples taken from
areas near ocean ridges were younger than
samples taken from areas near deep-sea trenches.
This was indicated on their maps using lines called
isochrons, or lines on a map that connect points
(of sediments) that have the same age.
 Using sonar, topographic and age information
from the new technology, American Scientist
Harry Hess proposed Seafloor Spreading in the
mid-1900s. His theory states that new ocean crust
is formed at ocean ridges and destroyed at
deep-sea trenches.
**Note: Seafloor Spreading was the missing link
needed by Wegener to complete his model of
continental drift.
 (A) Yellow is new
(seafloor ) crust
created at the ocean
ridge (where magma
breaks through the
ocean floor)
 (B) Red is new crust;
older crust (yellow) has
been moved away
 (C) Yellow is new crust;
older crust continues to
move away from the
ocean ridge