Download Lithosphere

Lithosphere
Last Time
• Last class we discussed:
– Internal structure of the Earth
• Crust
• Mantle
• Core
– The four spheres that make up the planet
– Biosphere
– Hydrosphere
– Atmosphere
– Lithosphere
A CLOSER LOOK AT THE
LITHOSPHERE
From last class
• Lithosphere:
– The outer shell of the Earth comprising the
crust and the upper mantle
• The lithosphere includes things like:
•
•
•
•
Rocks, minerals, soil
Mountains
Plains
Volcanoes
Essential to Life
• The lithosphere is not just a pile of rocks
• It is vital to life:
• Place for plant roots to take hold and get vital
minerals
• Offers a range of habitats for animals to live in
• Has natural resources that humans use (oil,
natural gas, precious rocks, etc)
• Has soil that humans need to grow their crops
A moving landscape
• We may think of mountains and continents
to permanent fixed structures
BUT they’re not!
• The Earth’s surface is in constant motion
Under Pressure
• Due to heat and pressure the Earth’s
crust is moving:
– Rising
– Sinking
– Folding
– Fracturing
DRIFTING SLOWLY
Has our planet always looked
the way it does today?
How are mountains created?
What causes earthquakes?
A little History
• In the early 20th century Alfred Wegener
was studying the continents
• As he was studying some maps, he
realized that the different continents
seemed to be pieces in a giant jig-saw
puzzle
Does this mean all the
continents were once
connected?!
More Evidence
• He also noticed that there were mountain
chains in Europe and in North America
that were the same age and had the
same types of rocks…
…was this all one mountain range
once?
More Evidence
• Wegener also found fossils of the same
animals in very distant countries
– There was no way the same animal could
have evolved in two places!
– There was also no way that it swam across
the ocean
The continents MUST
have all been
connected together
at some point
How is this possible?
Continental Drift!
Pangaea
• Wegener suggested that all of today’s
continents must have once been
connected to form one super continent
that he name Pangaea
– Pangaea must have eventually broken apart
and the different continents drifted apart to
their present locations
Lack of Explanation
• The problem was that Wegener could not
demonstrate what force would cause the
continents to shift
• And so his ideas were mostly refused by
the scientific community at the time
Years later
• A little while later sonar was invented
– This allowed scientists to see the ocean floor
and they were able to see continental
shelves (the under water extensions of the
continents) and oceanic ridges (under water
mountains)
• The edges of the continental shelves fit even better
together!
Asthenosphere
• Scientists then also discovered the
asthenosphere
– (from last class) the upper part of the mantle
that is semi-liquid
– They discovered that the continents float
around on top of the asthenosphere
Plate Tectonics
• Along came John Tuzo Wilson (a
Canadian!) in 1965 and put it all together
– He modified the continental drift theory to
take into account these recent findings
– He said the Earth’s crust is divided into vast
rigid plates that are able to move
• Tectonic plates
But how or why do
these plates move?
Convection!
Convection
• From last class:
– The inside of the Earth gets progressively
hotter
• From our unit on matter:
– A hotter substance is less dense than
colder versions of the same substance
– This means that hotter rocks are less
dense than cold rocks
What happened in the density
lab?
Which substances were on top?
The more dense or the less
dense?
Convection
• Denser substances sink
• Less dense substances float
So….
• Hot magma rises from the lower
mantle to the top
• It then gets pushed to the side by
more hot magma; moving the plates
floating on it
Convection currents
We’re going to do a
lab on this!
Plate Movement
• Plates move at a rate of about 1cm to
20cm per year
– This is why we don’t really notice it!
• Move in three ways:
• Convergent
• Divergent
• Transform fault
Plate Movement
Stress and Pressure
• All this movement puts a lot of pressure
on the Earth’s crust
• When the pressure becomes too much
you get things like:
• Mountains forming
• Earthquakes
• Volcano eruptions
Lava Video
Mountain Formation
Volcanoes
Earthquakes