Question

what first caused people to consider that the continents were once one large landmass?
○ glacier evidence in warmer countries
○ continents looked like they fit together
○ studying the valleys of the ocean floor
○ similar fossils were found on many continents

Explanation:

The initial observation that sparked the idea of a single ancient supercontinent was the visual similarity in the shapes of continental coastlines (like Africa and South America appearing to interlock), which predated other supporting evidence like fossil or glacial data.

Answer:

continents looked like they fit together