Simplify the following text for a Grade 12 native English-speaking person.
Original: Several seals discovered at Indus Valley Civilization ( c. 3300 â `` 1700 BCE ) sites in Pakistan depict figures in positions resembling a common yoga or meditation pose , showing `` a form of ritual discipline , suggesting a precursor of yoga , '' according to archaeologist Gregory Possehl .
Simplified: Several seals discovered at Indus Valley Civilization ( c. 3300 â `` 1700 B.C.E. ) sites in Pakistan depict figures in positions resembling a common yoga or meditation pose , showing `` a form of ritual discipline , suggesting a precursor of yoga '' , according to archaeologist Gregory Possehl .