Simplify the following text for a Grade 8 native English-speaking person.
Original: A clear rock painting in Ginga Wardelirrhmeng , on the northern edge of the Arnhem Land plateau , from the freshwater period shows a didgeridoo player and two songmen participating in an Ubarr Ceremony .
Simplified: A rock painting in Ginga Wardelirrhmeng , on the northern edge of the Arnhem Land plateau , dates from the freshwater period . It shows a didgeridoo player and two singers playing in a ceremony .