The change from thinking the continents are stationary to understanding that the outer layer of the earth moves slowly nearly all of the time occurred primarily because

We began to make global observations that required recognition that the continents and oceans had not always been in their current positions.

Explanation:

Scientist began to study the earth and notice that the continents and oceans had not always been in their current positions. This variation in the continents and oceans position is accountable for all kind of occurrences, such as formation of mountains, earthquakes and volcanoes. All these ideas, and many more, are circumscribe in an idea called plate tectonics.