Seafloor Spreading

  • Ocean floor moves like a ______carrying continents with it.
  • ______ocean floor forms along cracks in the ocean crust as molten material erupts from the mantle spreading out and pushing ______rocks to the sides of the crack. New ocean floor is constantly added by the process of ______.

Evidence of Seafloor Spreading

1. ______– Rocks shaped like pillows (rock pillows) show that molten material has erupted again and again from cracks along the mid-ocean ridge and cooled quickly.

  • The ______the most extensive chain of mountains on earth, but more than ______of this mountain range lies in the deep ocean. The mid-ocean ridge wraps around the globe for more than 65,000 km like the seam of a baseball.

2. ______ – Rocks that make up the ocean floor lie in a pattern of magnetized stripes which hold a record of the reversals in Earth’s magnetic field

3. ______– Core samples from the ocean floor show that older rocks are found farther from the ridge; youngest rocks are in the center of the ridge

Sea-Floor Spreading – ______in the 1960’s; the process that continually adds new material to the ocean floor while pushing older rocks away from the ridge.

Plate Tectonics

According to the theory of plate tectonics, the earth’s outer shell is not one solid piece of rock. Instead the earth’s crust is broken into a number of ______. The plates vary in size and thickness.

  • These plates are not anchored in place but ______over a hot and bendable layer of the ______.

Tectonic Plates

  • These tectonic plates are ______.
  • There are 3 types of plates

Divergent:

Convergent:

Transform:

Plate Boundaries

Divergent Boundary:

  • Boundary between two plates that are ______.
  • Features of Divergent Boundaries are:

Convergent Boundaries: 

  • Boundaries between two plates that are ______.
  • Three Types

Ocean to Continent: Ocean plate collides with Continent Plate

Subduction Zones:

Volcanoes

Ocean Plates are more ______than the Continent plates

Ocean to Ocean: Ocean plate collides with another ocean plate

The ______dense plate slides under the ______dense plate creating a subduction zone creating a ______.

Island arcs are formed

Continent to Continent

Plates push ______forming ______.

Transform Boundaries: ↓↑

  • Boundaries between plates that ______past one another.
  • ______occur at this boundary.
  • What’s the most active transform boundary in the U.S.? ______.