Download Earth Science Notes - Bridgman Public Schools

Earth Science Notes
Seafloor Spreading
PT and Seafloor Spreading
• The PT Theory was not accepted at first
because there was no explanation for how
the continents moved.
– Scientist did not know yet about convection
cells or the information we discussed in our
last lecture.
• After a while, evidence began to mount for
seafloor spreading. This provided an
explanation for what moved the continents.
Evidence for Seafloor Spreading:
Magnetic Reversals
• During World War II,
sensitive instruments called
magnetometers were
developed to help detect
steel-hulled submarines.
When research scientists
used magnetometers to
study the ocean floor, they
discovered a surprising
pattern. Measurements of
magnetic variations
showed that, in many
areas, alternating bands
of rocks recording normal
and reversed polarity
were arranged
symmetrically about midocean ridges
Evidence for Seafloor Spreading:
Magnetic Reversals
• Magnetic Reversals
– The Earth has a magnetic north pole and a
magnetic south pole.
– These poles have flipped periodically in
Earth’s past.
• This means the north pole has become the south
pole and vise versa.
– The record of the reversal of the magnetic
field is preserved in magnetic rocks which lie
along the ocean floor.
Evidence for Seafloor Spreading:
Magnetic Reversals
• Magnetism in the
Earth is created by
– Magnetic material
– Currents
• A bar of iron can be
made into a magnet by
wrapping it with wires
and running a current
through the wires.
Evidence for Seafloor Spreading
Evidence for Seafloor Spreading
Evidence for Seafloor Spreading:
Age of Rock
• Rocks samples taken near the Mid-Ocean
ridges show that rock to be the youngest
on Earth.
• Rocks increase in age as the get farther
away from the mid-ocean ridges.
Evidence for Seafloor Spreading:
Age of Rock
Evidence for Seafloor Spreading
Summary
Lets talk about the main points of what we
just discussed.