Transcript Plate Tectonics - dhsearthandspacescience

Plate Tectonics
What evidence supports the idea of
plate tectonics? (5 reasons)
1. The Earth’s modern day continents seem to ‘fit’
together
2. Fossils of similar species were found on
continents that are now separated by a great
distance
3. Evidence of glaciers exists in parts of the world
that do not currently experience freezing
temperatures (this implies that landmasses
move throughout time)
What evidence supports the idea of
plate tectonics? (5 reasons)
4. Paleomagnetic studies of Earth’s past magnetic
fields suggest the magnetic north pole has
changed. A parsimonious (simple) explanation
is that landmasses have moved, NOT the north
pole. Stripes within magnetite (magnetic
magma mineral) imply movement of materials
in the lithosphere
5. Seismometers used for weapons testing after
WWII showed a pattern of earthquake and
geologic activity. This suggests boundary lines
What is a mobilist? What is an antimobilist?
• People (geologists) that believe the features of
the Earth is a result of massive global
contraction and expansion are called ANTIMOBILISTS
• People (geologists) that believe the Earth is
made of moving pieces are MOBILISTS
What was Pangaea? Approximately how
long ago did it exist?
• The ‘SUPERCONTINENT’ existed about 225
million years ago
What are the names of the two
‘pieces’ of Pangaea during the Triassic
period?
• Laurasia and Gondwanaland
Supercontinent Cycle
• Supercontinent cycle: The aggregation and
dispersal of Earth’s continental crust in 300-500
million year cycle
• Wilson cycle: Describes the periodic opening
and closing of ocean basins
• Although complementary, the Supercontinent
cycle is more compelling since the oldest
seafloor is dated 170 million years ago and the
oldest continental crust is dated 4 billion years.
What drives the movement of plates?
• The movement of plates is driven by convection
currents within the Earth
Push
How are the two major ocean masses,
the Atlantic and Pacific, changing?
• The Atlantic ocean is getting wider and the
Pacific ocean is becoming narrower
*** The Pacific ocean may close in the future and
form the Mega Pacific Ocean through tectonic
interactions. This Mega ocean will surround the
new supercontinent.
(~250 000 000 years)
When was the theory of plate
tectonics formulated?
• 1960’s and 1970’s
How many tectonic plates exist? What
are their names?
• 14 major plates + 38 minor plates = 52 plates
How fast do plates move?
• 2 – 10 cm per year
3 Types of plate boundaries.
• Convergent boundaries describe compression
• Divergent boundaries describe extension
• Transform boundaries describe sliding or
irregular interaction
Boundary between Eurasian and
North American continental
tectonic plates
San Andreas Fault –
Transform Boundary
Types of crust
• Oceanic crust surfaces underneath ocean basins.
▫ Thin
▫ Dense
▫ Continually made at mid-ocean ridges
• Continental crust exists above water and at
shallow sea beds
▫ Thick
▫ Low density
Subduction
• Subduction refers to the movement of one plate
under another plate at a convergent boundary
3 types of convergent boundaries
Type of convergent
boundary
Result
Oceanic crust – Oceanic One plate subducts the
crust
other
Oceanic crust –
Continental crust
Oceanic crust subducts
the continental crust
Continental –
Continental crust
Both plates DO NOT
subduct and result in
heavy folding
The Andes Mountains
• The Nazca plate crashed into South America
• This is a convergent boundary resulted in the
South American landmass being crunched into a
mountain range and a depression forming off
the coast of the Pacific Ocean
The Himalayan Mountains
• The Himalayan mountains are an example a
mountain range created through convergent
boundary interactions.
• Between the Australian (Indian) plate and the
Eurasian plate
Test Yourself
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Read Section 4.2
Answer Questions: 1-5 on pg. 77
Complete Chapter 4 Review on pages 78 and 79
Questions #1-14, Critical Thinking Questions 1-4