What made Wagener believe the continents may have all been one unit?

In 1912 Alfred Wegener (1880-1930) noticed the same thing and proposed that the continents were once compressed into a single protocontinent which he called Pangaea (meaning "all lands"), and over time they have drifted apart into their current distribution.

Answerair masses develop near the equator are warm; tropical air mass

Answer cumulus clouds;