Simplify the following text for a Grade 7 native English-speaking person.
Original: It was created when Exxon and Mobil , both companies formed after the John D. Rockefeller 's original Standard Oil company split apart , joined together in a merger to become one company .
Simplified: It is a direct descendant of John D. Rockefeller 's Standard Oil company , and was formed on November 30 , 1999 , by the merger of Exxon and Mobil .