Simplify the following text for a Grade 16 native English-speaking person.
Original: However , Wegener was unable to demonstrate a mechanism for continental drift , which , combined with his mostly circumstantial evidence , meant that his hypothesis was not accepted until the 1950s , when numerous discoveries provided evidence of continental drift .
Simplified: However , at the time he was unable to demonstrate a mechanism for this movement ; this combined with not enough solid evidence meant that his hypothesis was not accepted until the 1950s , when numerous discoveries provided evidence of continental drift .