i can understand continental drift what’s the sea got to do with it? · 2020-02-07 · how does...
TRANSCRIPT
What’s the sea got to do with it?
I can understand
what sea-floor
spreading is by
using evidence
from the
Continental Drift
Theory.
3 IMPORTANT THINGS to LOOK for and KNOW
1. What is seafloor spreading?2. Which scientist suggested that seafloor
spreading supported the Continental Drift Theory?
3. How does Seafloor Spreading support the Continental Drift Theory?
Mid-Ocean Ridges ● What are they?
Mid-Ocean Ridges curve
like the seam of a
baseball along the Earth’s
sea floor. They are very
similar to mountains and
valleys in the ocean.
Sonar Sonar - short for Sound Navigation and Ranging, helps to explore and map the ocean because sound waves travel farther in the water than do radar and light waves.
Sonar A device that
bounces sound waves
off underwater
objects and then
records the echoes
of these sound
waves.
The time it takes
for the echo to
arrive indicates
the distance from
the object.
Harry Hess **● The mapping of mid-ocean
ridges made scientists
curious to know more about
them by trying to explain
how they are formed.
● Harry Hess, an American
geologist was curious
about mid-ocean ridges.
Harry Hess ● He began to think about the ocean floor
in relation to the problem of
continental drift.
● In the 1960’s Hess suggested that the
continents do move in a process called
sea-floor spreading.
Sea-floor Spreading
Sea-Floor SpreadingThe sea floor spreads
apart along both sides of
a mid-ocean ridge as new
crust is added.
As a result, the ocean
floors move like
conveyor belts, carrying
the continents along
with them.
Sea-Floor Spreading **
Molten material erupts through the
valley that runs along the center of some
mid-ocean ridges.
This material hardens to form rock on the
ocean floor.
Stop and Think?So, what happens to
the rock along the
ridge when new
molten material
erupts?
Evidence of Seafloor Spreading** Several types of evidence support
Hess’s theory of seafloor
spreading.
★ Eruptions of Molten Material
★ Magnetic Strips in rock of the
ocean floor.
★ The ages of rocks themselves.
Eruptions of Molten Material ● In the 1960’s, scientists found evidence that new
material is indeed erupting along mid-ocean
ridges.
● During their deep water dive in a specialized
submarine (Alvin) they discovered strange rocks
shaped like pillows and toothpaste that had been
squeezed out of the tube.
Eruptions of Molten Material● Such rocks only form when molten material harden
quickly after erupting underwater.
● These rocks showed that molten material has
erupted again and again along the mid ocean
ridge.
Magnetic Strips in rocks of the ocean floor● Scientists discovered
the rocks that make up
the ocean floor lies
in a pattern of
magnetized “stripes.”
Magnetic Strips in rocks of the ocean floor● The rock on the ocean floor contain bits of iron.
When the new molten rock being to harden and
take form the bits of iron line up in the
direction of the Earth’s magnetic poles giving
the rocks permanent “magnetic memory.”
The Age of Rocks Themselves ● This proof came from rock samples obtained by
drilling into the ocean floor.
● They found that the farther away from a ridge the
samples were taken, the older the rocks were.
● The youngest rocks were always in the center of the
ridges.
How does seafloor spreading support the theory of continental drift?
In your notebook: Please answer the
following question. You must use complete
sentences and explain your understanding
of the material presented. This will be
graded for a 10 point homework grade.