What is Seafloor Spreading?

Sea floor spreading is the process of an ocean floor growing in size. Not all ocean floors are expanding. The Atlantic ocean is expanding, but the Pacific Ocean is shrinking.

How Does Seafloor Spreading Happen?

The Atlantic Ocean floor is spreading because of underwater mountain ranges called mid ocean ridges. Mid ocean ridges form where two tectonic plates meet. The mid-Atlantic ridge is a mid ocean ridge that runs through the Atlantic Ocean. This ocean ridge makes the Atlantic ocean floor grow. Magma from the mantle bubbles up from cracks in the ocean ridges. When magma reaches  the surface of the Earth’s crust, it cools down and hardens to form rock. This newly formed rock pushes older rock to the sides, causing the ocean floor to spread. This is why the rock closest to mid ocean ridges is the newest, and rock farther away from ocean ridges was formed a longer time ago.

What is Subduction?

Subduction is the process of rock in the sea floor to sink back into the mantle. This process takes over a hundred thousand years. As the sea floor is spreading, it forces old rock downward and forms deep ocean trenches. Ocean floor rock goes back into the mantle at these ocean trenches.

Why is the Pacific Ocean Sinking?

The Pacific Ocean is the largest ocean in the world, but it is shrinking. This is because subduction is happening faster than magma cools to form rock. In other words, rock is sinking back into the mantle faster than rock is being created at mid ocean ridges.

How Does Seafloor Spreading Provide Evidence for Wegener’s Theory?

Alfred Wegener hypothesized that all the continents were connected into one supercontinent more than a billion years ago. No one believed him, because he could not come up with a cause that separated the continents. Seafloor spreading provides evidence for Wegener’s theory. Seafloor spreading is caused by the movement of  plate tectonics. This movement provides a force that could have broken the supercontinent into the pieces of the modern continents.