The massive eruptions which formed the traps were one of the largest known volcanic events of the last 500 million years of Earth history . They continued for a million years and spanned the Permian-Triassic boundary , about 251 to 250 million years ago . The massive eruptive event which formed the traps , one of the largest known volcanic events of the last 500 million years of Earth 's geological history , continued for a million years and spanned the Permian -- Triassic boundary , about 251 to 250 million years ago .