The crust and upper mantle make up Earth's ____.

Scientists have observed that the continents move apart or come together at speeds of a few centimeters per ____.

Seafloor spreading occurs because ____.

A vast, underwater mountain chain is called a(n) _________.

What particular event is shown on the picture?

What technology did scientists use in the mid-1900s to map the mid-ocean ridge?

In sea-floor spreading, molten material rises from the mantle and erupts

The process by which the ocean floor sinks beneath an deep-ocean trench and back into the mantle is known as

The process of ___________ continually adds new crust to the ocean floor along both sides of the mid-ocean ridge.

What kind of plate boundary is shown on the picture?

The scientist credited with sea-floor spreading is _________

The ocean floor sinks beneath a deep-ocean trench and back into the mantle in a process known as ________.

What is formed at the subduction zone?