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 got space travel and could see the motions
◦ we began to make global observations that required recognition that the continents and oceans had not always been in their current positions
◦ we improved our surveying instruments significantly
◦ we had two world wars and learned a lot from them about the oceans that explained how continents moved