Download Objectives: Describe seafloor spreading. Relate how age and

Objectives:
Describe seafloor spreading.
Relate how age and magnetic clues
confirm seafloor spreading.
Harry Hess’ theory “seafloor spreading” states
that molten material erupts along valleys in the
ocean ridges. The sea floor spreads apart as
new crust is added. (1963)
Earth behaves like a giant magnet, and from
time to time in history, the poles have reversed
themselves. If it happened today, your
compass needle would point south instead of
north.
When molten material cools, the bits of iron
line up in the direction of the magnetic poles.
The idea of Polarity was discovered in
1963 by Fred Vine and
Drummond Matthews.
Up until the 1950’s, little was
known about the ocean floor.
When echo sounding devices
were invented, detailed maps
could finally be drawn.
Marie Tharp and Bruce Heezen
were the first discover the midocean ridge.
SONAR
SOund Navigation And Ranging
(Science starting working on the
idea around 1914 and perfected it
around the 1930- 1940.
In 1968 the research ship Glomar Challenger
obtained rock samples. They found no rocks that
were older than 180 million years old. Continental
rocks are 4 billion years old. They also studied the
rocks located at the mid ocean ridge. These
rocks were the youngest.
By looking at these
rocks, scientist can tell
when the magnetic
reversals occurred by
using a magnetometer.
This evidence shows us
the same pattern occurs
on both sides of the
mid-ocean ridge,
proving that the sea
floor is moving.