Notes on Seafloor
Spreading
1. What were the opinions of
most scientists about the
topography…
the mid-1900’s, most
scientists thought that the
ocean floor was essentially flat.
 Until
2. Which technology allowed
scientists to map the ocean
floor?

Echo-sounding technology, such as
SONAR, uses sound waves to measure
water depth. The sound waves bounce
off the ocean floor and back to a
receiver.
3. Which 2 features of the ocean
floor were discovered…


Vast underwater mountain chains called
mid-ocean ridges were discovered in
places such as the Atlantic Ocean.
Deep-sea trenches that are thousands of
kilometers long and up to 11 km. deep
were found in the Pacific Ocean.
Analysis Of Seafloor Rocks
1.
The ages of seafloor rocks vary. Those
rocks near mid-ocean ridges are younger
than those near deep-sea trenches.
-Ocean floor rock is only about 180 million
years old.
-Where is the ocean crust from earlier
oceans?
Analysis Of Seafloor Rocks
2.
The thickness of ocean floor sediment
is only a few hundred meters.
-Why aren’t seafloor sediments as thick
as continental sediments?
-Could the thin blanket of ocean
sediment be the result of the age of the
ocean crust?
5. Describe Hess’ theory of
seafloor spreading


New ocean crust is formed at mid-ocean
ridges, and older ocean crust is destroyed at
deep-sea trenches. Magma is forced up at
ocean ridges and hardens to form new crust.
As spreading along a ridge continues, it forces
old crust into the trench, where it turns back
into magma due to heat and pressure.
6. How is seafloor spreading the
“missing link” in plate
tectonics?

Seafloor spreading explains how the
continents move. They are riding atop
the oceanic crust as the seafloor
spreads apart at mid-ocean ridges.