Simplify the following text for a Grade 9 native English-speaking person.
Original: On 8 June 1924 George Mallory and Andrew Irvine made an attempt on the summit via the North Col\/North Ridge\/Northeast Ridge route from which they never returned .
Simplified: On June 8th , 1924 , George Leigh Mallory and climbing partner Andrew Irvine made an attempt on the summit of Mount Everest .