Simplify the following text for a Grade 12 native English-speaking person.
Original: Because of the fertile soil the area around Soest was occupied long before 836 when the village is first mentioned in the Dagobertsche Schenkung , although the origin of this document is historically uncertain .
Simplified: Due to the fertile soil the area around Soest was used long before 836 when the village is first mentioned in the Dagobertsche Schenkung , although the origin of this document is historically unknown .