Simplify the following text for a Grade 6 native English-speaking person.
Original: Since 1867 , Tornero was the only editor of El Mercurio de ValparaÃ so until 1870 , when he partnered with Camilo Letelier .
Simplified: Tornero was the only editor of El Mercurio de ValparaÃ so from 1867 to 1870 . In 1870 , he partnered with Camilo Letelier .