Geographical time videos

After watching the geographical time videos, I learnt that the continents moved a lot through the past and they continue to move. Some of the places that were icy and now tropical forests, some of continents less dense crust float on the water like ice burgs. There's more facts that I found interesting that I learnt from the videos but those were the ones I found the more interesting. Although, I would like to know how scientists thought the continents moved when technology wasn't the best many years ago?