K67 was a meteorite that nearly hit Earth in 2009, thus completely destroying it. This meteorite was going to be to bounced off the atmosphere by Mr Smith.
However, The Trickster intervened, Andrea Yates was existing instead of Sarah Jane Smith. Without Sarah Jane, Mr Smith wouldn't exist, thus K67 would then destroy the Earth.
When The Trickster was defeated, Sarah Jane existed once more and the meteor bounced off the Earth. (SJA: Whatever Happened to Sarah Jane?)