Download ES2 Sea floor spreading Name: Introduction: About 30 years ago

ES2 Sea floor spreading
Name:
Introduction: About 30 years ago scientists noticed patterns on the ocean floor. They
found that new sea floor was created at mid-ocean ridges at divergent boundaries. The
farther away from these boundaries, the older the ocean floor gets. A second pattern was
due to magnetism. At midocean ridghes magma rises to the surface and cools and hardens
to form rock. When it hardens, the rock acts like a compass and points in the direction os
the magnetic field of the Earth. Rocks forming today point North, but at times in the past
they pointed South. On either side of the midocean ridge is a mirror image of magnetic
patterns and ages of rock. This gave evidence for Sea Floor spreading and plate
tectonics.
While new crust is created at divergent boundaries, it gets destroyed where plates collide
at convergent boundaries. Here “subduction” occurs where one plate sinks underneath
another and deep trenches form. The sinking plate eventually melts into the mantle.
Purpose: you will simulate movement at convergent and divergent boundaries to see the
rock patterns that occur at each boundary.
Procedure:
1. Find the sheet of sea floor spreading model patterns and color the sections of the
patterns as indicated.
2. Carefully cut along the DOTTED lines (not the solid lines) to create two
multicolored long strips that should be identical.
3. Tape together the orange colored ends of each strip to create one very long strip.
4. Carefully cut slits A, B and C on the other half of the pattern
5. Thread the taped paper strips through Slit B, beginning with he untapped blue
ends. Pull one side through lit A and then the other side through slit C
6. Pull the thrips through the slits so that the same colors on both strips are coming
out of strip B and different matching colors are disappearing into slits A and C
Questions:
1. What kind of plate boundary does slit B represent?
2. What type of feature is represented at slit B? What is happening at that feature?
3. What type of feature is represented at slits A and slit C? What is happening at this
feature?
4. If each color on your strips of paper represent different ages of rock, which color is
youngest?
Which color is oldest?
5. A and C represent convergent boundaries, would these have old ocean floor or young
ocean floor?
6. New seafloor is continually being formed at mid-ocean ridges and old sea floor rock is
continually destroyed at ocean trenches. Continental crust cannot sink because it isn’t
dense enough and is too thick to sink into the mantle. Would you expect the average age
of continental rocks to be older or younger than oceanic rocks?
7. The Earth is 4.6 billion years old. How come the ocean floor rocks are less than 200
million years old?
Look at the map labeled “Age of the Rocks on the Atlantic ocean sea floor” to
answer the remaining questions
1. Where are the oldest rocks of the Atlantic ocean floor found?
How old are they (use the key)?
2. Where are the youngest rocks in the Atlantic ocean found?
How old are they (use the key)?
3. Is the middle of the Atlantic likely a convergent boundary or is it a divergent
boundary? Explain how you can tell.
4. The oldest rocks between Africa and South America are ____________million
years old. The oldest rocks between North America and Africa are
__________million years old. Based on this evidence, what part of Pangaea
began to break apart first: the northern part or was it the Southern part?