Simplify the following text for a Grade 13 native English-speaking person.
Original: Study of these rocks shows that the eon featured massive , rapid continental accretion ( unique to the Proterozoic ) , supercontinent cycles , and wholly-modern orogenic activity .
Simplified: Study of these rocks shows that the eon featured massive , rapid continental accretion ( unique to the Proterozoic ) , supercontinent cycles , and mountain building .