Simplify the following text for a Grade 10 native English-speaking person.
Original: It was essentially coincident with the Permianâ `` Triassic extinction event , which is estimated to have killed 90 % of species existing at the time .
Simplified: It was the same time as the Permianâ `` Triassic extinction event , which is estimated to have killed 90 % of species existing at the time .